VOL. 102 | NO. 8 AUGUST 2021 WORLDS PREMIERE The launch of a long-awaited telescope is going to throw back the curtains. Who is first in line to look?

Picnic Below​ a Lava Light Show

Flood Forecasting in India

Science by Sailboat

FROM THE EDITOR

Editor in Chief Heather Goss, [email protected] Unveiling the Next Exoplanet Act AGU Staff Vice President, Communications, Marketing, and Media Relations Amy Storey he whole field of exoplanet study is frustratingly tantaliz- Editorial ing. We now know for sure there are alien worlds. We can Managing Editor Caryl-Sue Micalizio see them! Kinda. We see their shadows; we can see their Senior Science Editor Timothy Oleson T Associate Editor Alexandra Scammell fuzzy outlines. We are so close to the tipping point of having News and Features Writer Kimberly M. S. Cartier enough knowledge to truly shake our understanding—in the best News and Features Writer Jenessa Duncombe way, says this space geek—of Earth’s place in the universe. Production & Design The first light of the James Webb Space Telescope ( JWST) may Assistant Director, Operations Faith A. Ishii be what sends us over that exciting edge. In just a few months, Production and Analytics Specialist Anaise Aristide the much-­ ​­delayed launch will, knock on wood, proceed from Assistant Director, Design & Branding Beth Bagley French Guiana and take around a month to travel to its destina- Senior Graphic Designer Valerie Friedman Senior Graphic Designer J. Henry Pereira tion at the second Lagrange point (L2). “This is certainly an excit- ing time for exoplanet science, with current missions like Hubble Marketing and TESS [Transiting Exoplanet Survey Satellite] providing us Communications Specialist Maria Muekalia Assistant Director, Marketing & Advertising Liz Zipse with new discoveries and future missions like JWST, which promises to provide incredible new data that will answer some of our current questions and also create many new ones,” said Sarah Hörst of Johns Hopkins University, Eos’s Science Adviser representing AGU’s Planetary Sciences Advertising Display Advertising Steve West section who consulted on this issue. “The field is moving very quickly right now.” [email protected] That’s why our August issue is all about exoplanets—what we know and what awaits us over Recruitment Advertising [email protected] the launch horizon. Who gets the first peek through JWST? In March, the proposals selected for the first observing cycle were announced. Meet the slate of scientists who will be pointing the Science Advisers telescope at other worlds, and read what they hope to learn in “Overture to Exoplanets” on Geodesy Surendra Adhikari page 26. Geomagnetism, Paleomagnetism, and Electromagnetism Julie Bowles As with all new instruments, the data collected from JWST will be pieced together with obser- Natural Hazards Paula R. Buchanan vations from ongoing missions and other facilities around the world. “Over the last decade, we’ve GeoHealth Helena Chapman gotten gorgeous images from the ALMA interferometer in Chile and have seen loads of ­fine-scale​­ Atmospheric and Space Electricity Kenneth L. Cummins Cryosphere Ellyn Enderlin structure, tracing pebbles in ­planet-​­forming disks,” says astronomer Ilse Cleeves in our feature Space Physics and Aeronomy Jingnan Guo article. Hörst found this synergy with ALMA (Atacama Large Millimeter/submillimeter Array) History of Geophysics Kristine C. Harper especially intriguing: “Although I’ve thought a lot about what we’ll learn about individual plan- Planetary Sciences Sarah M. Hörst Volcanology, Geochemistry, and Petrology Emily R. Johnson ets, I hadn’t really thought much about what we’ll be able to learn about planet formation pro- Mineral and Rock Physics Shun-ichiro Karato cess by studying the disks themselves.” Societal Impacts and Policy Sciences Christine Kirchhoff In “The Forecast for Exoplanets Is Cloudy but Bright,” on page 34, we learn the immense chal- Seismology Ved Lekic Tectonophysics Jian Lin lenge posed by exoplanet atmospheres, when researchers are still struggling to understand the Near-Surface Geophysics Juan Lorenzo complex dynamics of clouds on our own planet. And in “Exoplanets in the Shadows” on page 20, Earth and Space Science Informatics Kirk Martinez we look at the rogues, the extremes, and a new field being coined as necroplanetology. Ocean Sciences Jerry L. Miller What awaits us when the first science results start coming in from JWST and all the coordi- Study of the Earth’s Deep Interior Rita Parai Education Eric M. Riggs nated missions next year? “I’m really excited for the unexpected,” says Hörst. “I’m excited for Global Environmental Change Hansi Singh all the ‘well, that’s weird’ moments. Those are my favorite things in science because that’s when Hydrology Kerstin Stahl you know that new discoveries are going to be made. I’m also really happy for all of my colleagues Paleoceanography and Paleoclimatology Kaustubh Thirumalai Nonlinear Geophysics Adrian Tuck who have worked so tirelessly for so many years to make JWST happen.” Biogeosciences Merritt Turetsky We’re pretty happy, too, for the scientists long awaiting this day and for the rest of us who Hydrology Adam S. Ward eagerly await a wide new window on our mysterious universe. Diversity and Inclusion Lisa D. White Earth and Planetary Surface Processes Andrew C. Wilcox

©2021. AGU. All Rights Reserved. Material in this issue may be photocopied by individual scientists for research or classroom use. Permission is also granted to use short quotes, figures, and tables for publication in scientific books and journals. For permission for any other uses, contact the AGU Publications Office. Eos (ISSN 0096-3941) is published monthly except December by AGU, 2000 Florida Ave., NW, Washington, DC 20009, USA. Periodical Class postage paid at Washington, D.C., and at additional mailing offices. POSTMASTER: Send address changes to Heather Goss, Editor in Chief Member Service Center, 2000 Florida Ave., NW, Washington, DC 20009, USA Member Service Center: 8:00 a.m.–6:00 p.m. Eastern time; Tel: +1-202-462-6900; Fax: +1-202-328-0566; Tel. orders in U.S.: 1-800-966-2481; [email protected]. Submit your article proposal or suggest a news story to Eos at bit.ly/Eos-proposal. Views expressed in this publication do not necessarily reflect official positions of AGU unless expressly stated. Randy Fiser, Executive Director/CEO

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Features

20 Exoplanets in the Shadows 26 Overture to Exoplanets By Damond Benningfield By Kimberly M. S. Cartier

The universe is full of wonderful weirdness, and we’re Who is in the front row to get a glimpse of what the only just starting to find it. James Webb Space Telescope will show us?

On the Cover 34 The Forecast for Exoplanets The seven small, potentially rocky worlds of the ­TRAPPIST-1 Is Cloudy but Bright system orbit an M dwarf star, shown in an artist’s rendering. By Kate Evans Credit: NASA/JPL-Caltech We can see 159 light years away, but how do we get through the final few miles?

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Columns

From the Editor AGU News 1 Unveiling the Next Exoplanet Act 41 In Appreciation of AGU’s Outstanding Reviewers of 2020 News 5 Gaps in Exoplanet Sizes Shift with Age Research Spotlight 6 Chasing Magma Around Iceland’s Reykjanes Peninsula 51 South Pole Ice Core Reveals History of Antarctic Sea Ice | 8 Vestiges of a Volcanic Arc Hidden Within Chicxulub Carbonate Standards Ensure Better Paleothermometers Crater 52 ‘Oumuamua May Be an Icy Fragment of a Pluto-Like 9 Indian Cities Prepare for Floods with Predictive Exoplanet | A 50,000-Year History of Current Flow Yields Technology New Climate Clues 11 Climate Clues from One of the Rainiest Places on Earth 12 Studying Arctic Fjords with Crowdsourced Science Editors’ Highlights and Sailboats 53 Dune Aurora Explained by Combined Satellite–Ground 13 A New Tool May Make Geological Microscopy Data Observations | Urban Vegetation a Key Regulator for Heat More Accessible Island Intensity 15 Forecasters Navigate a Highway to Success Around Lake Victoria Positions Available Opinion 54 Current job openings in the Earth and space sciences 17 “Earth Cousins” Are New Targets for Planetary Materials Research Crossword Puzzle 56 Distant Wanderers

AmericanGeophysicalUnion @AGU_Eos company/american-geophysical-union AGUvideos americangeophysicalunion americangeophysicalunion

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Gaps in Exoplanet Sizes Shift with Age

wenty-​­six years ago, astronomers dis- covered the first planet orbiting a dis- ­Ttant Sun-­ ​­like star. Today thousands of exoplanets are known to inhabit our local swath of the Milky Way, and that deluge of data has inadvertently revealed a cosmic mys- tery: Planets just a bit larger than Earth appear to be relatively rare in the exoplanet canon. A team has now used observations of hun- dreds of exoplanets to show that this plane- tary gap isn’t static but instead evolves with planet age—younger planetary systems are more likely to be missing slightly smaller planets, and older systems are more apt to be without slightly larger planets. This evolution is consistent with the hypothesis that atmo- spheric loss—literally, a planet’s atmosphere blowing away over time—is responsible for this ­so-called​­ “radius valley,” the researchers suggested.

Changes with Age In 2017, scientists reported the first confident detection of the radius valley (­­bit​.ly/­ ​­gap​ -­radius). (Four years earlier, a different team had published a tentative detection; ­bit​.­ly/​ ­tentative​-detection.)­ Defined as a relative paucity of exoplanets roughly 50%–​­100% larger than Earth, the radius valley is readily determine the planets’ ages, which they A Moving Valley apparent when looking at histograms of assessed indirectly by estimating the ages When David and his collaborators looked planet size, said Julia Venturini, an astro- of their host stars. (Because it takes just a few at the distribution of planet sizes in each physicist at the International Space Science million years for planets to form around a star, group, they indeed found a shift in the radius Institute in Bern, Switzerland, not involved these objects, astronomically speaking, have valley: Planets within it tended to be about in the new research. “There’s a depletion of very nearly the same ages.) 5% smaller, on average, in younger planetary planets at about 1.7 Earth radii.” systems compared with older planetary sys- Trevor David, an astrophysicist at the Flat- tems. It wasn’t wholly surprising to find this iron Institute in New York, and his colleagues evolution, but it was unexpected that it per- were curious to know whether the location of “There’s a depletion of planets sisted over such long timescales [billions of the radius valley—that is, the planetary size at about 1.7 Earth radii.” years], said David. “What was surprising was range it encompasses—evolves with planet how long this evolution seems to be.” age. That’s an important question, said David, These findings are consistent with planets because finding evolution in the radius valley losing their atmospheres over time, David could shed light on its cause or causes. It’s and his colleagues proposed. The idea is that been proposed that some planets lose their The team calculated planet ages ranging most planets develop atmospheres early on atmospheres over time, which causes them from about 500 million years to 12 billion but then lose them, effectively shrinking in to change size. If the timescale over which the years, but “age is one of those parameters size from just below Neptune’s (roughly radius valley evolves matches the timescale that’s very difficult to determine for most 4 times Earth’s radius) to just above Earth’s. of atmospheric loss, it might be possible to stars,” David said. That’s because estimates “We’re inferring that some ­sub-Neptunes​­ are pin down that process as the explanation, of stars’ ages rely on theoretical models of being converted to super-­ ​­Earths through said David. how stars evolve, and those models aren’t atmospheric loss,” said David. As time goes In a new study published in the Astronomical perfect when it comes to individual stars, he on, larger planets lose their atmospheres, Journal, the researchers analyzed planets orig- said. For that reason, the researchers decided which explains the evolution of the radius inally discovered using the Kepler Space Tele- to base most of their analyses on a coarse valley, the researchers suggested. scope (­bit​.­ly/​­exoplanet​-­size​-­distribution). division of their sample into two age groups, They focused on a sample of roughly 1,400 one corresponding to stars younger than a Kicking Away Atmospheres ­ com/ ​­ oorka planets whose host stars had been observed few billion years and one encompassing stars Atmospheric loss can occur via several mech-

​ . iStock spectroscopically. Their first task was to older than about ­2–3 billion years. anisms, scientists believe, but two in partic-

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ular are believed to be relatively common. Both involve energy being transferred into a Chasing Magma Around Iceland’s planet’s atmosphere to the point that it can heat to thousands of degrees kelvin. That Reykjanes Peninsula input of energy gives the atoms and mole- cules within an atmosphere a literal kick, and some of them, particularly lighter species like hydrogen, can escape. “You can boil the atmosphere of a planet,” said Akash Gupta, a planetary scientist at the University of California, Los Angeles not involved in the research. In the first mechanism—photoevapora- tion—the energy is provided by X-ray­ and ultraviolet photons emitted by a planet’s host star. In the second mechanism—core cool- ing—the source of the energy is the planet itself. An assembling planet is formed from successive collisions of rocky objects, and all

“Age is one of those parameters that’s very difficult to determine for most stars.”

of those collisions deposit energy into the forming planet. Over time, planets reradiate that energy, some of which makes its way into their atmospheres. Theoretical studies have predicted that Icelandic Meteorological Office seismologist Kristín Jónsdóttir stands on solidified black basalt that glows red photoevaporation functions over relatively from erupting Fagradalsfjall volcano behind her. Credit: Kristín Jónsdóttir short timescales—about 100 million years—while core cooling persists over bil- lions of years. But concluding that core cooling is responsible for the evolution in n December 2019, Reykjanes Peninsula, Soon thereafter, the Icelandic Meteorolog- the radius valley would be premature, said which juts into the Atlantic Ocean south- ical Office’s seismic network recorded more David, because some researchers have sug- Iwest of Iceland’s capital city of Reyk- than 50,000 earthquakes on the peninsula. gested that photoevaporation can also act javík, began experiencing intense seismic Using the monitoring tools at their disposal, over billions of years in some cases. It’s swarms. Since then, scientists at the Icelandic scientists found a corridor of magma between hard to pinpoint which is more likely at Meteorological Office have been tracking and Keilir and Fagradalsfjall, said Barsotti. This play, said David. “We can’t rule out either monitoring deformation of Earth’s surface as magma flowed underground for approxi- the photoevaporation or core-­ ​­powered magma intruded into the shallow crust. Three mately 3 weeks, with earthquakes defining mass loss theories.” initial intrusions occurred near Mount Thor- the edges of the subterranean chamber. Then It’s also a possibility that the radius valley björn, just outside the town of Grindavík. A both seismicity and deformation plummeted. arises because of how planets form, not how fourth slightly inflated the peninsula’s west- At that point, some scientists hypothesized they evolve. In the future, David and his col- ernmost tip, and a fifth leapfrogged back east, that the intrusion would freeze within the leagues plan to study extremely young plan- beyond Grindavík, to Krýsuvík, according crust, said Kristín Jónsdóttir, a seismologist at ets, those only about 10 million years old. to Sara Barsotti, an Italian volcanologist and the Icelandic Meteorological Office. “Then,” These youngsters of the universe should pre- coordinator for volcanic hazards at the Ice- she said, “the eruption started.” serve more information about their forma- landic Meteorological Office. tion, the researchers hope. More than a year after this unrest began, Keeping Crowds Safe on 24 February 2021, a large earthquake mea- On 19 March, lava began to erupt from the suring magnitude 5.7 jolted the peninsula edge of the intrusion near Fagradalsfjall, and By Katherine Kornei (@KatherineKornei), between Keilir and Fagradalsfjall volcanoes, Icelanders flocked to the mountains above Science­ Writer “marking a turning point,” Barsotti said. the fissure to picnic, play football, or simply

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Against a gray sky, orange lava pours and pops out of Fagradalsfjall on the second day of the eruption. In the foreground, cooling lava glows against the black basalt that’s already solidified. Credit: Toby Elliott/Unsplash

observe nature’s lava light show. “Iceland- DAS, to monitor seismicity near Mount Thor- coauthor and a geophysicist at Helmholtz ers…feel this is part of their life,” said Bar- björn. In April, Sebastian Heimann, a scien- Centre Potsdam, describing previous work sotti. “They really want to enjoy what their tist at Helmholtz Centre Potsdam in Ger- using the same cable near Mount Thorbjörn country is capable [of giving] them.” many, presented the latest results from (bit­ .​ ly/­ imaging​­ -​ cables).­ In that study, Jous- Because crowds continue to visit the erup- the ongoing study at the 2021 Annual Meet- set and his colleagues, including Blanck, tion, the Icelandic Meteorological Office ing of the Seismological Society of America. compared the catalog of earthquakes meets daily with Iceland’s Department of At a molecular level, DAS works because recorded by both DAS and traditional seis- Civil Protection and Emergency Management ­fiber-​­optic cables contain impurities, mic stations. to ensure the safety of volcano watchers, Bar- explained Hanna Blanck, one of Heimann’s “Propagating magma increases the pres- sotti explained. A rescue team is always pres- coauthors and a doctoral student at the Uni- sure in the surrounding crust, causing many ent, and they use handheld sensors to detect versity of Iceland. A laser pulse sent through small earthquakes,” said Blanck. More data gases that could be dangerous. a cable will encounter these impurities, she mean detecting more small earthquakes, “The big challenge,” Barsotti said, is “[fore- said. When that happens, the light scatters, which should yield a better picture of magma seeing] the opening of new vents.” What and a small portion returns toward the laser movement. began as a single vent now boasts a fissure source. By continuously measuring the However, “[DAS] is still in its research swarm, cones, and lava fields. “People should returning signal, scientists can look for phase,” said Jónsdóttir, “so it’s not being be [able] to go, but [we must keep] them far changes that indicate the cable has moved. routinely used by monitoring agencies.” In away from what we consider to be hazardous.” Earthquakes have distinct signatures that the future, she said, it will likely comple- The Icelandic Meteorological Office keeps help differentiate them from, for example, ment more established methods in seismol- vigil over this volcano with a variety of tech- the rumble of a passing car. ogy. niques. For example, InSAR (interferometric DAS provides several advantages to tradi- Nevertheless, seismologists and volcanol- synthetic aperture radar), a ­satellite-​­based tional seismic networks, including higher ogists often investigate secrets of Earth that method, allows scientists to measure differ- spatial resolution, said Blanck. Traditional cannot be seen, Jónsdóttir said, so holding a ences in topography at centimeter scale. GPS seismic networks are spaced kilometers apart, freshly formed piece of basalt as lava spews stations help track how the ground itself whereas the spatial resolution Heimann used in the background—after hypothesizing the moves. Passive satellite imagery can trace the along the ­21-kilometer-long​­ cable was a scant existence of an intrusion in that very loca- progress of toxic clouds, like sulfur dioxide. 4 meters. tion—provides incredible validation. “We caught more small earthquakes Seismic Monitoring of the Future compared to the conventional methods Geoscientists from across Europe have been [likely because] we have many more records By Alka Tripathy-­ ​­Lang (@DrAlkaTrip), Science exploring distributed acoustic sensing, or along the fiber,” said Philippe Jousset, a Writer

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Vestiges of a Volcanic Arc Hidden Within Chicxulub Crater

bout 66 million years ago, an asteroid core includes 600 hurtled through Earth’s atmosphere meters of the peak A at approximately 20 kilometers per ring, said Gulick, second—nearly 100 times the speed of who serves as ­co– sound—and slammed into water and lime- chief scientist of stone off Mexico’s Yucatán Peninsula, cata- Expedition 364. lyzing the demise of the dinosaurs. The In a recent study solid rock hit by the asteroid momentarily published in the behaved like a liquid, said University of Texas Geological Society at Austin geophysicist Sean Gulick. Almost of America Bulletin, instantaneously, a massive transient crater Catherine Ross, a extended to the mantle, and rocks from doctoral student 10 kilometers deep rushed to the sides of the at the University hole. They slid back toward the crater’s cen- of Texas at Austin; ter and shot 20 kilometers into the air before Gulick; and their collapsing outward again. As the rock flowed coauthors deter- outward, it regained its strength and formed mined the age a peak ring, resulting in mountains encir- of the peak ring cling the center of the 200-­ kilometer-​­ wide​­ granites—334 mil- Chicxulub crater. lion years old— and unraveled an unexpected history of arc magmatism The story of these rocks “turned and superconti- nent reconstruc- out to be completely separate tion (bit­ ​.ly/­ ​­arc​ from the story of the impact -­magma). The crater.” story of these rocks, said Gulick, “turned out to be completely sepa- rate from the story In 2016, at a cost of $10 million, scientists of the impact cra- (a) The amalgamation of Pangea. Laurentia, in brown, lies to the north. Gondwana, participating in International Ocean Discov- ter.” The tale is shown in gray, lies to the south. Numerous terranes, shown in purple, were caught ery Program Expedition 364, in collaboration told by tiny crys- between the ancient continents of Laurentia and Gondwana. The Yucatán lies in with the International Continental Scientific tals of zircon— the midst of these terranes, and a pink star indicates the Chicxulub impact site. Drilling Program, extracted an ­835-​­meter-​ small clocks within CA = Colombian Andes; Coa = Coahuila; M = Merida terrane; Mx = Mixteca; Oax = ­long drill core from the Chicxulub crater. The rocks—that record Oaxaquia; SM = Southern Maya. (b) A simplified cross section through Laurentia, various chapters of the Rheic Ocean, and subduction off the edge of the Yucatán crust. The Rheic Earth’s history. Ocean must subduct below the Yucatán to create the arc magmatism responsible for the zircons Ross analyzed. Ga = ­giga-​­annum; Ma = ­mega-​­annum. Credit: Ross Getting Past a et al., 2021, ­https://​­doi​.org/​­10.1130/B35831.1 Shocking Impact As a melt solidifies, said Ross, zirco- nium, oxygen, and silicon atoms find each The drill core granites, however, harbor an other to form zircon. Trace atoms of radioac- incredible amount of damage caused by the tive uranium easily swap places with zirco- impact’s shock wave. “The energy of Chic­ nium while excluding lead (the product of xulub is equivalent to 10 billion times the size uranium decay). By measuring both uranium of a World War II era nuclear bomb,” said and lead, geochronologists like Ross can cal- Gulick. Highly damaged zircons from the culate when lead began to accumulate in the peak ring yield the impact age, he said, but Zircons, like this one with laser ablation points, crystal. In zircons of granitoids, this date typ- “once you go below those highest shocked record the storied history of the Chicxulub crater. ically records when the grain crystallized from grains, you more faithfully record the original Credit: Catherine H. Ross the melt. age and not the impact age.”

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The zircons that Ross and colleagues tar- geted lacked microstructures that indicate Indian Cities Prepare for Floods shock, said Maree McGregor, a planetary sci- entist at the University of New Brunswick with Predictive Technology who was not involved in this study. “A lot of people would overlook this material when they’re trying to understand impact crater- ing,” she said, because past studies focused heavily on the impact age and not the history of the target rocks. Ross incrementally bored into 835 individ- ual zircons with a laser, measuring age as a function of depth to differentiate age domains. “Being able to visualize the data and separate [them] in that way is…critical when you’re trying to establish different ages for different regional tectonic events,” said McGregor.

“The energy of Chicxulub is equivalent to 10 billion times the size of a World War II era nuclear bomb.”

Chennai, India, was pummeled by more than 483 millimeters (19 inches) of rain in a single day in 2015. Credit: Ancient Ocean, Volcanic Arc Veethika, Wikimedia, CC ­BY-SA 4.0 (­bit​.­ly/​­ccbysa4-0) In addition to the ­334-​­million-​­year-​­old Car- boniferous zircons, Ross found three older populations. Crystals with ages ranging from 1.3 billion to 1 billion years ago fingerprint rban floods in India have caused fatal- upstream region; river, tidal, and storm surge the formation of the supercontinent Rodinia. ities, injuries, displacement, and modeling; and a ­high-resolution​­ digital ele- After Rodinia fragmented, ­550-million-​­ year-​­ ​ Uenormous economic losses. Cities vation map of the city, Ghosh said. ­old zircons place the Yucatán crust near the across the country are now investing in ­high-​ A consortium of scientists from 13 research mountainous margins of the West African ­tech tools to better model and forecast these institutes and government organizations craton, which was part of the supercontinent natural hazards. worked on these separate aspects and Gondwana. Zircons between 500 million and In 2015, the metropolis of Chennai faced together developed India’s first fully auto- 400 million years old document deformation devastating floods responsible for the deaths mated real-­ ​­time flood forecasting system, as these crustal bits moved across the ancient of more than 500 people and displacement of launched in 2019. Rheic Ocean toward Laurentia, which today more than a million more. Financial losses “We generated 800 scenarios of flood and corresponds to the North American conti- reached around $3 billion. The extent of the tide conditions,” Ghosh said. “When the nental core, Ross said. damage prompted the Indian government to model receives a weather forecast from the As the Rheic oceanic slab subducted, fluids approach scientists to develop a flood fore- National Centre for Medium Range Weather drove partial melting that powered a volcanic casting system for the city. Forecasting, it will search and find the closest arc on the edge of the Yucatán crust, said Subimal Ghosh, a professor of civil engi- scenario. If there is a chance of flood, the Ross. Using trace element geochemistry from neering at the Indian Institute of Technology model will predict the vulnerable sites for the individual grains, she found that in spite of Bombay, led the efforts. Chennai’s topogra- next 3 days.” their tumultuous impact history, Carbonifer- phy makes it particularly vulnerable, Ghosh Sisir Kumar Dash is a scientist at the ous zircons preserve volcanic arc signatures. said. In addition to being a coastal city, Chen- National Centre for Coastal Research (NCCR) This research, said coauthor and geo­ nai has many rivers and an upstream catch- in Chennai, which is responsible for the oper- chronologist Daniel Stockli, is very tedious ment area from which water flows when there ation of the model. “We analyze daily rainfall micrometer-­ ​­by-​­micrometer work. But ulti- is heavy rainfall. data, and if there is a probability of inunda- mately, he said, these finely detailed data illu- tion, the model is run and alerts are sent to minate processes at the scale of plate tectonics. Forecasting in Chennai the state disaster management department,” The city’s topography determines where he said. inundation occurs and made the development Since the tool was implemented, however, By Alka Tripathy-­ ​­Lang (@DrAlkaTrip), Science of a flood forecasting system complex. The Chennai has not experienced heavy rainfall, Writer system had to include the hydrology of the so it has not been put to a strong test.

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Forecasting in Bengaluru World Resources Institute who was not The tool also has a mobile application, Bengaluru, formerly known as Bangalore, has involved in flood forecasting in Chennai Bengaluru Megha Sandesha (BMS), seen some success with its own flood fore- or Bengaluru. He had a sober view of the which can be accessed by officials and resi- casting system, according to scientists at the projects. “A good model is not about the tech dents for ­real-​­time information about Indian Institute of Science (IISc) in Bengaluru or visualization that come with it,” he said. rainfall and flooding. and the Karnataka State Natural Disaster Instead, it’s “about the ability to help in the Mujumdar added that “short-­ ​­duration, Monitoring Centre. The organizations devel- decisionmaking process, which hasn’t ­high-​­intensity floods are increasing in oped the system together. been successfully demonstrated in India.” Indian cities and happen very quickly— P. Mujumdar, a professor of civil engineer- Shubha Avinash, scientific officer at within ­15–20 minutes—due to climate ing at IISc who led the work, said that “­short-​ the Karnataka State Natural Disaster Moni- change and urbanization. Similar models ­duration rainfall forecasts from various toring Centre, said the forecasting model was should be developed for all cities.” weather agencies were combined with our still an effective tool: “The forecast model has Last year, India’s Ministry of Earth Sci- hydrology model—which has high-­ resolution​­ served as a better decision support system for ences developed a flood warning sys- digital elevation maps of the city—and infor- administrative authorities in disaster pre- tem for the Mumbai region, iFLOWS-­ ​ mation on drainage systems and lakes.” paredness, postflood recovery, and response ­Mumbai, which is likely to be operational this ­Real-​­time rainfall data are obtained actions in heavy rain events faced by the year. through a network of 100 automatic rain city in recent years.” Avinash oversees the “Cities need to have a proper road map,” gauges and 25 water level sensors set operation of the Bengaluru flood model. Bhagat said, “with not just the model up on storm water drains at various ­flood-​ Avinash added that the alerts help city as the target but an integrated response ­vulnerable areas across Bengaluru. The officials take timely, ­location-specific​­ action. plan (both short term and long term). model, however, is unable to make reliable For instance, the city power company (Ban- It should start with the creation and seam- predictions if the rainfall is sudden and didn’t galore Electricity Supply Company Lim- less sharing of related data in the public appear in the forecast, Mujumdar added. ited, or ­BESCOM) makes use of the wind domain.” speed and direction forecasts to ascer- Scaling Up tain which areas would have a probability Raj Bhagat Palanichamy is a senior manager of fallen electric lines and shuts down power By Deepa Padmanaban (@deepa_padma), at the Sustainable Cities initiative of the supply to ensure safety. Science­ Writer

10 Eos // AUGUST 2021 NEWS

Climate Clues from One of the Rainiest Places on Earth

Alejandro Jaramillo, a hydrologist at the Center for Atmospheric Sciences at the National Autonomous University of Mexico, said that more observations will allow for a better model, which will lead to better pre- diction of rainfall and major weather events, like hurricanes. Jaramillo was not involved in the new research. “If you better understand the processes that are causing this high rainfall, you can find better ways for climate models to fill in the gaps where there [aren’t] hard data,” Jara­millo said. The Pacific Ocean off the coast of Nuquí, Chocó, Colombia, is one of the rainiest spots on Earth. Credit: Andreas Philipp, CC ­BY-NC-ND 2.0 (­bit​.­ly/​­ccbyncnd2-0) Impacts Beyond Climate According to Germán Poveda, a coauthor on the recent study and a professor at the National University of Colombia, the project jet stream known as the Chocó ­low-​ not only aimed to understand the dynamics ­level jet (the ChocoJet) connects the and thermodynamics that explain the rainiest A Pacific Ocean with western Colombia. region on Earth but also was an opportunity to It helps dump more than 9,000 millimeters train Colombia’s next generation of climate of rain each year, making the area offshore of scientists. the Colombian town of Nuquí one of the rain- Juliana Valencia Betancur, for instance, was iest places on the planet. an undergraduate environmental engineer- “The ChocoJet—this ­low-​­level flow—is a ing student at Colegio Mayor de Antioquia in physical bridge between the sea surface tem- Medellín during the Nuquí field campaign. peratures and sources of moisture in the She and a half dozen other undergraduate Pacific, and the climate patterns of western students helped prepare and launch balloons South America,” said John Mejia, an associate as part of their undergraduate research expe- research professor of climatology at Nevada’s rience. Desert Research Institute and lead author of “I hadn’t had much interest in atmospheric a new paper on the phenomenon. science, but after Nuquí, with all the marvel- In addition to its regional impact, the ous things I learned, my outlook changed ChocoJet plays a role in the El ­Niño–Southern​­ completely, and my professional career Oscillation (ENSO), a climate pattern whose changed course,” she said, adding that she is variations can signal droughts and floods for Students from Institución Educativa Ecoturistica Lito- now looking for graduate opportunities in Colombian farmers. ENSO also has significant ral Pacifico in Nuquí prepare to launch a sonde bal- atmospheric science. impacts on Europe, Africa, Asia, and North loon during the fieldwork campaign. Credit: Organi- Johanna Yepes, a coauthor and researcher America. zation of Tropical East Pacific Convection (OTREC) based at Colegio Mayor de Antioquia, said that “In the atmosphere, we are all connected,” participants/John Mejia Nuquí’s local schoolchildren also benefited Mejia said, and the ChocoJet “is part of the from the project’s outreach activities. During engine that redistributes the heat from the the field campaign, the researchers visited tropics to higher latitudes.” Nuquí’s only school and, with enthusiastic standing of the dynamics and thermodynam- support of the principal, presented their proj- Rainy Puzzle ics of the ChocoJet’s processes, which have ect to students in the fourth to seventh In 2019, after 6 months of preparations, Mejia implications for regional wildlife and agricul- grades. The students were also invited to visit and his team were able to get enough helium ture, as well as for natural hazards. Mejia said the launch site and got a chance to launch a tanks and sonde balloons to this remote region, the main contribution of the field campaign sonde balloon themselves. which is accessible by only sea or air. They in Nuquí and the resulting data was to find out “For me, it was the most beautiful part, put- launched the balloons up to four times a day why and how these precipitation mechanisms ting what we were doing in very simple words over 51 days, resulting in new data on tempera- produce one of the rainiest places on Earth, and seeing how the children understood the ture, winds, and other atmospheric conditions. with the added benefit of building on the very daytime cycle of rain, sometimes even better They detailed their findings in a recent scant climate data gathered previously. “This than we did ourselves,” Yepes said. paper published in the Journal of Geophysical is a field experiment that can help test cli- Research: Atmospheres (­bit.​ ­ly/rainy​­ -​ ­chocojet). mate models…. Figuring this out can make The new data contribute to a better under- global models more accurate,” Mejia said. By Andrew J. Wight (@ligaze), Science Writer

SCIENCE NEWS BY AGU // Eos.org 11 NEWS

Studying Arctic Fjords with Crowdsourced Science and Sailboats

n June 2017, Nicolas Peissel led the 13-meter­ sailboat Exiles out of port in St. John’s, New- Ifoundland and Labrador, Canada. The ves- sel sailed north to Greenland and into the remnants of Tropical Storm Cindy. Peissel and several other crew members are aid workers for Doctors Without Borders, but they were on a 3-month­ scientific—not medical—expe- dition aboard Exiles. The expedition explored the feasibility of crowdsourced science using sailboats to expand data collection in fjords affected by the melting Greenland Ice Sheet. Daniel Carlson,

“Scientific work was historically, and should continue to be, undertaken by members of the general public.” Exiles, whose crew collected data on fjords in the Arctic, anchors near a receding glacier in 2017. Credit: Daniel Carlson

an oceanographer at Germany’s Helmholtz-­ ​ ­Zentrum Hereon and science officer for the boats also require much less fuel, lessening­ the their affordability and versatility and would expedition, sailed on Exiles for a month. After environmental impact of Arctic research. like to see more people with sailboats taking he left, the crew of nonscientists continued Together, the Exiles crew took 147 CTD part in research. “It’s not like you can just collecting data. The expedition log and pre- measurements. Carlson also took aerial pho- make your own thing—you need the instru- liminary results were published in Frontiers in tographs of icebergs with a drone to estimate ments—but I think there would be interest Marine Science (­bit​.­ly/​­arctic​-­sailing). the rate at which they melt. He said this from citizen scientists,” Bouchard said. The melting ice in Greenland is increasing wouldn’t have been possible on a research Although it takes experienced sailors to the amount of fresh water in fjords, which cruise with tight schedules and timelines. navigate in the Arctic, more sailboats than changes the salinity and mixing of ocean ever have been heading north, which could water. Scientists don’t fully know what Crowdsourcing Science in the Arctic bring new opportunities for amateur scien- impact these changes will have on the marine Carlson collected ­much-​­needed data on tists. Peissel said that sailors in the Arctic ecosystem. changes occurring in fjords as a result of melt- usually have an intense connection to the sea To study what contributes meltwater to the ing ice. The expedition also demonstrated that and nature. “These are the people who are ocean, scientists measure the conductivity, crowdsourced science is a viable option for more than likely to say, ‘Hey, why don’t you temperature, and depth (CTD) of the water expanding Arctic oceanography research. put your instruments on board?’” column, but reaching these remote fjords to “We were extremely happy that we could Following their study’s success, Carlson and take measurements on research ships is collaborate with a professional scientist in a Peissel are planning another expedition to the expensive and treacherous. Ships also often scientific institution,” said Peissel, who is a Arctic in 2022. “The scientific discipline, just carry several research teams with conflicting coauthor on the paper. “But we also wanted like humanitarianism, does not uniquely experimental needs and schedules. These to be the citizens that could produce raw, reli- belong to the scientist or the humanitarian,” limitations leave gaps in our understanding able scientific data, and we proved that.” The Peissel said. “Scientific work was historically, of the changing Arctic waters. crew took 98 CTD measurements after Carl- and should continue to be, undertaken by “Since you’re spending so much money on son left. members of the general public.” a research cruise, there’s usually a push to visit Caroline Bouchard, a fisheries scientist at as many fjords as possible,” Carlson said, “but the Greenland Institute of Natural Resources with the sailboat, you’re able to just stop and who wasn’t involved in the study, also uses By Andrew Chapman (@andrew7chapman), investigate things you find interesting.” Sail- sailboats for Arctic research. She appreciates Science­ Writer­

12 Eos // AUGUST 2021 NEWS

A New Tool May Make Geological Microscopy Data More Accessible

t all started with a problem many geosci- A technical report on the device, named The software also does not replicate all the entists faced in 2020. ­PiAutoStage, was recently published in Geo- different functions of a microscope, Rooney I Alex Steiner, a doctoral student at Mich- chemistry, Geophysics, Geosystems (­bit​.­ly/​­pi​ said. “You don’t have the ability to use a lot of igan State University, had research to do work- -­auto​-­stage). the advanced tools that are in a microscope that ing on thin sections—slivers of geological Because thin sections are also commonly help students identify ambiguous crystals.” materials that are usually analyzed under a used for instruction in geoscience lab courses, Despite these limitations, “from the per- microscope. But he and the two undergraduate ­PiAutoStage could also provide instructors a spective of a broad teaching tool, we think it’s students on the project were not allowed to new, affordable resource to digitize and use useful and in fact is different to a micro- access the lab or the geological samples they specimens and literary materials they already scope,” Rooney added. “Previously, students were working on because of the pandemic. have curated in their curriculum. would not have actually been able to see the It was out of this necessity that Steiner “I think this is a really nice approach to entire area of a microscope slide in a pan- helped develop a new tool that could automat- a problem that I heard a lot of people talking oramic image.” ically take pictures of entire thin sections and about last year when everything moved stitch them into digital panoramic microscope online,” said Anita Marshall, a geologist at images that could be analyzed anywhere. the University of Florida who was not involved in the study. “Anybody that had any “In a postpandemic world, sort of microscope work in their courses really struggled to move that work online.” devices like this could still be used for teaching. It allows Getting Microscopy Online students to have access to ­PiAutoStage consists of an open-­ source​­ mech- samples, for example, that anism that moves the sample around the microscope, attached to a ­high-​­resolution might be very valuable and can’t integrated camera and an inexpensive Rasp- be left in the lab, or there aren’t berry Pi computer. The researchers wrote enough thin sections for an computer code to take hundreds of ­high-​ entire group.” ­resolution images of an entire microscope sample and combine them into a single pan- orama. This technique allowed two undergraduate students—one at Michigan State University More Accessible Geoscience in East Lansing and another at Wayne State “In a postpandemic world, devices like this University in Detroit—to work collaboratively could still be used for teaching,” Rooney said. on the same project at the same time using ­PiAutoStage “allows students to have access the same thin sections of a flood basalt to samples, for example, that might be very sequence, said Tyrone Rooney, a geologist at valuable and can’t be left in the lab, or there Michigan State University and senior author aren’t enough thin sections for an entire of the paper. group.” And for the most part, the students enjoyed Although resources that can image micro- working with the microscope images online, scope samples already exist, they are often Steiner said. “Because the interface behaves prohibitively expensive: Microscopes with the same way as things like Google Earth or ­built-​­in or ­add-​­on cameras can cost tens of things like that. It’s just zoom in, zoom out, thousands of dollars. click and drag around. So they picked it up By contrast, because the ­PiAutoStage real quick. I don’t think anyone had any com- mechanism is entirely 3D printed, it would plaints, even with the very first lab we ran cost less than $200 to make the device, said These image mosaics of a fragment of Earth’s man- this year. Steiner, who was lead author of the report. tle were collected in optical arrangements with the One downside to long-distance micros- “You don’t have to order the parts from any- ­PiAutoStage: (a) ­plane-​­polarized light, (b) ­cross-​ copy, however, is its difficulty in replicating body or anything like that. You can liter- ­polarized light, and (c) ­cross-polarized​­ light at 45° of the collegiality that comes with the ability of ally make all of the hardware—it’s all printed rotation. Three sets of images permit students to “students to be able to shout across [the and assembled, [and] basically, it snaps examine minerals and rock textures in a way that room] to another student, ‘Hey, what’s together.” replicates the experience of using a petrographic this?’” said Rooney. The researchers tried to The system is also open source and made microscope. Credit: Steiner and Rooney, 2021, replicate this interaction by allowing students to be adaptable to almost any microscope. ­https://​­doi​.­org/​­10.1029/​­2021GC009693 to share panorama views with one another. The researchers have set up a ­PiAutoStage

SCIENCE NEWS BY AGU // Eos.org 13 NEWS

A crystal-​­rich lava from northern Kenya was captured in ­cross-​­polarized light. The lava contains abundant, chemically zoned clinopyroxene crystals that record a history of magma interactions. Credit: Steiner and Rooney, 2021, ­https://​­doi​.­org/​­10.1029/​­2021GC009693

website detailing examples, instructions, and when we introduce a new tool, usually data “All the petrologists that have seen what FAQs to help others build their own device. follows.” this is have also responded with, ‘This is so The new technique could make future The images produced by PiAutoStage cool.’ In fact, that word seems to be one that research into thin sections more accessible, have one additional benefit. is used quite an awful lot,” he added. Rooney said. “With more of these devices “Just looking at the thin section imag- out there, more innovations will happen sim- ery that I’ve taught with for years in a differ- ply because more people are trying to use it. ent way, I’ve seen them in a different way,” By Richard J. Sima (@richardsima), Science I don’t know what will happen. All I can say is, Rooney said. Writer

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14 Eos // AUGUST 2021 NEWS

Forecasters Navigate a Highway to Success Around Lake Victoria

ith the sight of a ­color-​­coded flag or the touch of a mobile phone W button, fishers and fish traders along the vast shores of Lake Victoria now know when it’s ideal to postpone a fishing trip or to buy less fish for the day. Four years of testing an early-­ warning​­ sys- tem (EWS) to inform fisherfolk in East Africa of approaching ­high-impact​­ weather events on Lake Victoria recently concluded. The High Impact Weather Lake System (HIGHWAY)­ project successfully demonstrated how improved weather, water, and climate ser- vices can save lives and livelihoods, as well as support socioeconomic development of vul- nerable communities. In 2017, the HIGHWAY­ project started on Lake Victoria, the largest of the African Great Lakes and the largest inland fishery on the continent. Lake Victoria’s 7,145-­ ​ ­kilometer-long shoreline is shared by Kenya, Tanzania, and Uganda. Fisheries employ between 500,000 and a million people A man raises a red flag, signaling severe weather, on the shores of Lake Victoria. Credit: Samuel Gatei/WMO from those countries as well as from neigh- boring nations Burundi and Rwanda and har- vest about a million metric tons of fish every year. early warnings that improved the lives of on the lake given that not all incidents are Lake Victoria’s size (it is the world’s communities living in the Lake Victoria reported,” said Paul Oloo, Kisumu County ­second-​­largest freshwater lake, behind only basin,” said Wilson. director of meteorology and assistant director Lake Superior in North America) allows it to “This ­early-​­warning system is a good thing of the Kenya Meteorological Department. generate its own weather patterns, some- for Lake Victoria, because according to Red times suddenly and with human and eco- Making the System nomic casualties. According to its website, As part of the project, the National Meteoro- ­HIGHWAY aimed to “enhance the resilience logical and Hydrological Services (NMHSs) of of African people and economic development “Thanks to the strong Kenya, Rwanda, Tanzania, and Uganda coop- to weather and climate related shocks, with erated in generating regular Lake Victoria an initial focus on the Lake Victoria Basin.” commitment, partnership, weather forecasts and severe weather warn- The project was funded by £4.5 million from and collaboration…we ings. the U.K. Department for International Devel- ­HIGHWAY supported the increase in avail- opment, under Weather and Climate Infor- succeeded in increasing ability of meteorological data and observa- mation Services for Africa. tions throughout the Lake Victoria basin. Of “HIGHWAY was an ambitious project that access to and use of note, the project contributed to the rehabili- spanned the entire weather and climate ser- codesigned early warnings tation of upper air stations in Lodwar and vices value chain—improving ­surface-​­based Nairobi, Kenya; Entebbe, Uganda; and Dar es observations, developing products to improve that improved the lives of Salaam, Tanzania. forecasting quality, and providing training on communities living in the The project also contributed to the avail- ­impact-​­based forecasts and warnings in the ability of such enhanced tools as ­high-​ Lake Victoria basin,” said Jay Wilson, head of Lake Victoria basin.” ­resolution modeling, as well as products, the Project Management and Implementation including Rapidly Developing Thunderstorm Division at the World Meteorological Organi- (which detects, tracks, characterizes, and zation (WMO). forecasts convective cells) and Convective “Thanks to the strong commitment, part- Cross statistics, about 5,000 people were dying Rainfall Rate (an algorithm based on the nership, and collaboration from all interna- annually [due to storms, strong winds, and assumption that high clouds with a large ver- tional and regional partners, we succeeded in large waves] prior to the year 2016. This figure tical extent are more likely to be raining). increasing access to and use of co-designed does not include all the deaths that occur Such products improve the accuracy of severe

SCIENCE NEWS BY AGU // Eos.org 15 NEWS

mation to plan fishing trips and other jour- neys on the lake,” said Wilson. In establishing the regional ­early-warning​­ system, standard operating procedures and ­impact-​­based warning methods were devel- oped jointly by partner states. Representa- tives from those states joined daily telecon- ferences so they could agree on severe weather warning information, but each partner state disseminated weather advisories in its area of jurisdiction. “We receive weather messages on our phones, and when you get an update, you send it to other people and put it on your WhatsApp status so that it can reach many fishermen,” said Mildred Shihanga, a fish trader in Kenya.

Saving Lives and Livelihoods “I think the EWS for Lake Victoria is a very Fisherfolk are among those most threatened by severe weather on Lake Victoria. Credit: Samuel Gatei/WMO good and important step to protect the lives and livelihoods of the communities that live around the lake,” said Nairobi-­ based​­ climate scientist Abubakr Salih Babiker of the Inter- weather forecasting in the basin, explained did not understand the message itself, Oloo governmental Authority on Development’s Wilson. said. Climate Prediction and Applications Centre, In contrast, “the ­early-​­warning informa- which provides climate services to 11 East Practical Outcomes tion passed currently to them is in a language African countries but is not part of the Because of the ­HIGHWAY enhancements, the and format that they can understand. ­HIGHWAY project. Uganda National Meteorological Authority is Weather warnings were co-designed with “The boats used by fishermen are small able to provide updates on thunderstorms and have no access to weather forecasts, and heavy rain over Lake Victoria in real time. especially when they are in the water. Now In Kenya and Tanzania, marine weather fore- the EWS gives them the forecast before and casts are now being disseminated specifically “The early-­ warning​­ information while they are in the water using mobile tech- to fishing communities twice per day. The nology,” Babiker said. “It also helps farmers forecasting offices of all three NMHSs also passed currently to [fisherfolk] is to plan better. It will help in saving lives and share their published forecasts through a in a language and format that livelihoods.” WhatsApp group. they can understand. Weather Rumelia Joshua, a fish trader in Tanzania, A three-­ ​­color traffic light flag system and warnings were co-designed with agreed. “The information helps us because notice boards are also used on beaches around when we get notified about bad weather, we the lake to describe the conditions expected them, standard weather buy fish in small quantities and save money,” during the forecast period. messages developed jointly, and she said. The flag signals help people without the weather information passed smartphones, said Ibrahim Mengo, a fisher- directly in its original format Scaling Up man in Uganda. “When I look at the forecast WMO and other supporters of the ­HIGHWAY and see the flag is green, then I know it’s OK using the WhatsApp platform.” project plan to scale it up to encompass to go, but when [the flag is] red or orange, I regional forecasting for all of East Africa, said know where I’m going is not safe and I decide Wilson. whether or not to go.” Babiker said ­HIGHWAY owes its success to them, standard weather messages developed the cooperation of the partner states as well Communication and Cooperation jointly, and the weather information passed as to forecast products that focus on the lake Efforts supported by HIGHWAY­ addressed directly in its original format using the itself as opposed to national systems. “In this improving communication and cooperation WhatsApp platform,” Oloo said. way, you get better products and better user in sharing meteorological data among orga- Innovations also included a “quick refer- services. If you are a fisherwoman on the lake, nizations and communities. Severe weather ence guide developed for translating standard you basically need the same information forecasts, participants said, could be incon- weather terms to local languages,” he added. regardless of your country,” he said. sistent: In some cases, fisherfolk did not Training sessions for forecasters, observ- receive any weather warning. In other cases, ers, and users in fishing communities have the fisherfolk did not take received weather built trust in the forecasts. “Communities are By Munyaradzi Makoni (@MunyaWaMakoni), information seriously, and sometimes they more confident in using the weather infor- Science Writer

16 Eos // AUGUST 2021 OPINION

“Earth Cousins” Are New Targets ​ for Planetary Materials Research

re the processes that generate plan- etary habitability in our solar system A common or rare elsewhere? Answer- ing this fundamental question poses an enor- mous challenge. For example, observing ­Earth-​­analogue exoplanets—that is, ­Earth-​­sized planets orbiting within the habitable zone of their host stars—is difficult today and will remain so even with the ­next-​­generation James Webb Space Telescope ( JWST) and ­large-​ ­aperture ­ground-based​­ telescopes. In coming years, it will be much easier to gather data on—and test hypotheses about the pro- cesses that generate and sustain habitability using—“Earth cousins.” These ­small-​­radius exoplanets lack solar system analogues but Fig. 1. Shown here are four common exoplanet classes that are relatively easy to characterize using observations are more accessible to observation because from existing telescopes (or telescopes that will be deployed soon) and that have no solar system analogue. they are slightly bigger or slightly hotter than Hypothetical cross sections for each planet type show interfaces that can be investigated using new laboratory

Earth. and numerical experiments. CO2 = carbon dioxide, Fe = iron, H2 = molecular hydrogen, H2O = water, Na = sodium. Here we discuss four classes of exoplanets and the investigations of planetary materials that are needed to understand them (Figure 1). Such efforts will help us better worlds, we need new experiments exploring Volatiles constitute a small fraction of a understand planets in general and Earth-­ like​­ the relevant planetary materials and condi- rocky planet’s mass, and quantifying their worlds in particular. tions. abundance is inherently hard. However, dif- Studying Earth cousin exoplanets can help ferent types of Earth cousin exoplanets offer What’s in the Air? us probe the delivery and distribution of ­life-​ natural solutions that can ease volatile detec- On exoplanets, the observable is the atmo- ­essential volatile species—chemical ele- tion. For example, on planets known as ­sub-​ sphere. Atmospheres are now routinely char- ments and compounds like water vapor and ­Neptunes, the spectroscopic fingerprint of acterized for ­Jupiter-​­sized exoplanets. And ­carbon-​­containing molecules, for example, volatiles could be easier to detect because of scientists are acquiring constraints for that form atmospheres and oceans, regulate their mixing with ­lower-​­molecular weight various atmospheric properties of smaller climate, and (on Earth) make up the bio- atmospheric species like hydrogen and worlds (those with a radius R less than sphere. Measuring abundances of these vol- helium. These lightweight species contribute 3.5 Earth radii), which are very abundant [e.g., atiles on cousin worlds that orbit closer to to more ­puffed-up​­ (expanded) and thus more Benneke et al., 2019; Kreidberg et al., 2019]. their star than the habitable zone is relatively detectable atmospheres. Hot, rocky exoplan- Soon, observatories applying existing meth- easy to do. These measurements are funda- ets could “bake out” volatiles from their inte- ods and new techniques such as ­high-​ mental to understanding habitability because riors while also heating and puffing up the ­resolution ­cross-​­correlation spectroscopy volatile species abundances on Earth cousin atmosphere, which would make spectral fea- will reveal even more information. exoplanets will help us understand volatile tures more visible. Disintegrating rocky plan- For these smaller worlds, as for Earth, a delivery and loss processes operating within ets may disperse their volatiles into large, and key to understanding atmospheric composi- habitable zones. therefore more observable, ­comet-​­like tails. tion is understanding exchanges between For example, rocky planets now within Let’s look at each of these examples fur- the planet’s atmosphere and interior habitable zones around red dwarf stars must ther. during planet formation and evolution. have spent more than 100 million years ear- This exchange often occurs at interfaces (i.e., lier in their existence under conditions Unexpected Sub-Neptunes surfaces) between volatile atmospheres exceeding the runaway greenhouse limit, About 1,000 ­sub-Neptune​­ exoplanets (radius and condensed (liquid or solid) silicate mate- suggesting surface temperatures hot enough of 1.­6-​­3.5 Earth radii) have been confirmed. rials. For many small exoplanets, these inter- to melt silicate rock into a magma ocean. So These planets, which are statistically about as faces exhibit ­pressure-​­temperature-​ whether these worlds are habitable today common as stars, blur the boundary between ­composition (P­ -​­T-​­X) regimes very different depends on the amount of ­life-essential​­ vol- terrestrial planets and gas giants. from Earth’s and that have been little atile elements supplied from sources farther Strong, albeit indirect, evidence indicates explored in laboratory and numerical exper- from the star [e.g., Tian and Ida, 2015], as well that the known sub-­ ​­Neptunes are mostly iments. To use exoplanet data to interpret the as on how well these elements are retained magma by mass and mostly atmosphere by origin and evolution of these strange new during and after the magma ocean phase. volume (for a review, see Bean et al. [2021]).

SCIENCE NEWS BY AGU // Eos.org 17 OPINION

these exoplanets, new experiments may also help reveal the potential for and drivers of magnetic fields on ­sub-Neptunes.​­ Such fields might be generated within both the atmo- sphere and the magma.

Hot and Rocky From statistical studies, we know that most stars are orbited by at least one roughly ­Earth-​­sized planet (radius of 0.75-­ ​­1.6 Earth radii) that is irradiated more strongly than our Sun’s innermost planet, Mercury. These hot, rocky exoplanets, of which about a thousand have been confirmed, experience high fluxes of ­atmosphere-stripping​­ ultraviolet photons and stellar wind. Whether they retain ­life-​ ­essential elements like nitrogen, carbon, and sulfur is unknown. On these hot, rocky exoplanets—and potentially on Venus as well—atmosphere-­ ​ ­rock or ­atmosphere-​­magma interactions at temperatures too high for liquid water will be important in determining atmospheric com- position and survival. But these interactions have been only sparingly investigated [Zolo- tov, 2018]. Many metamorphic and melting reactions between water and silicates under kilopascal to ­tens-​­of-​­gigapascal pressures are already known from experiments or are tractable Fig. 2. Ranges of plausible conditions at the interfaces between silicate surface rocks and volatile atmospheres using thermodynamic models. However, less on different types of worlds are indicated in thispressure– ­ ​­temperature (­P-​­T) diagram. Conditions on Earth, as well understood processes may occur in plan- well as other relevant conditions (critical points are the highest P-­ ​­T points where materials coexist in gaseous ets where silicate compositions and propor- and liquid states, and triple points are where three phases coexist), are also indicated. Mg2SiO4 = forsterite, an tions are different than they are on Earth, igneous mineral that is abundant in Earth’s mantle. meaning that exotic rock phases may be important. Innovative experiments and mod- eling that consider plausible exotic conditions will help us better understand these planets. This evidence implies that an interface data to help determine the equation of state Moreover, we need to conduct vaporization occurs, at pressures typically between 10 and (the relationship among pressure, volume, experiments to probe whether moderately 300 kilobars, between the magma and the and temperature), transport properties, and volatile elements are lost fast enough from molecular hydrogen (H2)-​­dominated atmo- chemical kinetics of ­H2-​­magma mixtures as hot, rocky planets to form a refractory lag and sphere on these planets. Interactions at and they might exist on these exoplanets. reset surface spectra. exchanges across this interface dictate the Because sub-­ ​­Neptunes are so numerous, chemistry and puffiness of the atmosphere. we cannot claim to understand the exoplanet Exotic Water Worlds? For example, water can form and become a ­mass-​­radius relationship in general (in Water makes up about 0.01% of Earth’s mass. significant fraction of the atmosphere, leading effect, the equation of state of planets in the In contrast, the mass fraction of water on to more chemically complex atmospheres. galaxy) without understanding interactions Europa, Ceres, and the parent bodies of car- Improved molecular dynamics calculations between H2 and magma on sub-­ Neptunes.​­ To bonaceous chondrite meteorites is some ­50-​ are needed to quantify the solubilities of gases understand the extent of mixing between H2, ­3,000 times greater than on Earth. Theory and gas mixtures in realistic magma ocean silicates, and iron alloy during ­sub-​­Neptune predicts that such ­water-​­rich worlds will be compositions (and in iron alloys composing assembly and evolution, we need more sim- common not only in habitable zones around planetary cores, which can also serve as res- ulations of giant impacts during planet for- other stars but in closer orbits as well. JWST ervoirs for volatiles) over a wider range of mation [e.g., Davies et al., 2020], as well as will be able to confirm or refute this theory pressures and temperatures than we have improved knowledge of convective processes [Greene et al., 2016]. studied until now. These calculations should on these planets. Within the ­P-​­T-​­X regimes If we could descend through the ­volatile-​ be backed up by laboratory investigations of of ­sub-Neptunes,​­ full miscibility between sil- ­rich outer envelope of a water world, we such materials using high-­ ​­pressure instru- icates and H2 becomes important (Figure 2). might find habitable temperatures at shallow mentation like diamond anvil cells. These Beyond shedding light on the chemistry depths [Kite and Ford, 2018]. Some habitable calculations and experiments will provide and ­magma-​­atmosphere interactions on layers may be cloaked beneath H2. Farther

18 Eos // AUGUST 2021 OPINION

down, as the atmospheric pressure reaches 10 month by a factor of 2 [Demory et al., 2016], From a practical standpoint, the scientific or more kilobars, we might encounter implying that it undergoes a global energy rewards of studying Earth cousins are ­low-​ ­silicate-​­volatile interfaces featuring super- balance change more than 10,000 times ­hanging fruit. critical fluids [e.g., Nisr et al., 2020] and con- greater than that from anthropogenic cli- ditions under which water can be fully misci- mate change on Earth. Such large swings Acknowledgments ble with silicates [Ni et al., 2017]. suggest that fast magma ­ocean-atmosphere​­ We thank the organizers of the ­AGU-​ We still need answers to several key ques- feedbacks operate on the planet. ­American Astronomical Society/Kavli work- tions about these worlds. What are the equi- To learn more about the chemical evolution shop on exoplanet science in 2019. libria and rates of gas production and uptake and physical properties of exoplanet magma for ­rock-​­volatile interfaces at water world seas, we need experiments like those used to References “seafloors”? Can they sustain a habitable cli- study ­early-​­stage planet formation, which Bean, J., et al. (2021), The nature and origins of sub-­ Neptune​­ size planets, J. Geophys. Res. Planets, 126(1), e2020JE006639, mate? With no land, and thus no continental can reveal information about silicate vapor- https://doi­ .org/​ 10­ .1029/​ 2020JE006639.­ weathering, can seafloor reactions supply ization and kinetics under the temperatures Benneke, B., et al. (2019), A sub-­ Neptune​­ exoplanet with a low-­ ​ ­life-​­essential nutrients? Do high pressures (1,­500-​­3,000 K) and pressures (10−5 to 100 metallicity­ methane-­ depleted​­ atmosphere and Mie-­ scattering​­ clouds, Nat. Astron., 3, 813–­ 821,​­ https://doi­ .org/​ 10­ .1038/​ s41550­ ​ and stratification suppress the tectonics bars) of magma planet surfaces. -019-­ 0800-​­ 5.​­ and volcanism that accelerate interior-­ ​ Exoplanets and exoplanetesimals that Davies, E. J., et al. (2020), Silicate melting and vaporization during rocky planet formation, J. Geophys. Res. Planets, 125(1), ­atmosphere exchange [Kite and Ford, 2018]? stray too close to their stars are destroyed— e2019JE006227, https://doi­ .org/​ 10­ .1029/​ 2019JE006227.­ As for the deep interiors of Titan and Gan- about five such cases have been confirmed. Demory, B.-O.,​­ et al. (2016), Variability in the super-­ Earth​­ 55 Cnc e, ymede in our own solar system, important These disintegrating planets give geoscien- Mon. Not. R. Astron. Soc., 455, 2,018–­ 2,027,​­ https://doi­ .org/​ 10­ ​ .1093/mnras/­ stv2239.­ open questions include the role of clathrates tists direct views of exoplanetary silicates Doyle, A., et al. (2019), Oxygen fugacities of extrasolar rocks: (compounds like methane hydrates in which because the debris tails can be millions of Evidence for an Earth-­ like​­ geochemistry of exoplanets, Science, one chemical component is enclosed within kilometers long [van Lieshout and Rappaport, 366, 356–­ 358,​­ https://doi­ .org/​ 10­ .1126/​ science­ .aax3901.​ Greene, T. P., et al. (2016), Characterizing transiting exoplanet a molecular “cage”) and the solubility and 2018]. For disintegrating planets that orbit atmospheres with JWST, Astrophys. J., 817, 17, https://doi­ .org/​ 10­ ​ transport of salts through ­high-pressure​­ ice white dwarf stars, the debris can form a gas .3847/0004-­ 637X/817/1/17.​­ layers. disk whose composition can be reconstructed Kite, E. S., and E. Ford (2018), Habitability of exoplanet water- worlds, Astrophys. J., 864, 75, https://doi­ .org/​ 10­ .3847/​ 1538­ ​ Experiments are needed to understand [e.g., Doyle et al., 2019]. -4357/aad6e0.​­ processes at water world seafloors. Metamor- To better read the signals of ­time-​­variable Kreidberg, L., et al. (2019), Absence of a thick atmosphere on the terrestrial exoplanet LHS 3844b, Nature, 573, 87–­ 90,​­ https://doi­ ​ phic petrologists are already experienced with disintegration, we need more understanding .org/10­ .1038/​ s41586-­ 019-​­ 1497-​­ 4.​­ the likely ­pressure-​­temperature conditions of how silicate vapor in planetary outflows Léger, A., et al. (2011), The extreme physical properties of the in these environments, and exoplanetary condenses and nucleates, as well as of frac- CoRoT-­ 7b​­ super-­ Earth,​­ Icarus, 213, 1–­ 11,​­ https://doi­ .org/​ 10­ .1016/​ j­ ​ .icarus.2011​ .02​ .004.​ studies could benefit from their expertise. tionation processes at and above disintegrat- Ni, H., et al. (2017), Supercritical fluids at subduction zones: Relative to rock compositions on Earth, we ing planets’ surfaces that may cause observed Evidence, formation condition, and physicochemical properties, should expect exotic petrologies on water compositions in debris to diverge from the Earth Sci. Rev., 167, 62–­ 71,​­ https://doi​ .org/​ 10­ .1016/​ j­ .earscirev​ ​ .2017.02​ .006.​ worlds—for example, worlds that are as bulk planet compositions. Nisr, C., et al. (2020), Large H2O solubility in dense silica and its sodium rich as chondritic meteorites. Knowl- implications for the interiors of water-­ rich​­ planets, Proc. Natl. Acad. Sci. U. S. A., 117, 9,747–9754, https://doi­ .org/​ 10­ .1073/​ pnas­ ​ edge gained through this work would not only Getting to Know the Cousins .1917448117. shed light on exoplanetary habitability but In the near future, new observatories like Norris, C. A., and B. J. Wood (2017), Earth’s volatile contents also open new paths of research into studying JWST and the European Space Agency’s established by melting and vaporization, Nature, 549, 507–­ 510,​­ https://doi.org/10.1038/nature23645. exotic thermochemical environments in our Atmospheric ­Remote-​­sensing Infrared Exo- Tian, F., and S. Ida (2015), Water contents of Earth-­ mass​­ planets solar system. planet ­Large-​­survey (ARIEL, planned for around M dwarfs, Nat. Geosci., 8, 177–­ 180,​­ https://doi­ .org/​ 10­ ​ launch in 2029) will provide new data. When .1038/ngeo2372.­ van Lieshout, R., and S. A. Rappaport (2018), Disintegrating Magma Seas and Planet Disintegration they do, and even now before they come rocky exoplanets, in Handbook of Exoplanets, pp. 1,527–­ 1,544,​­ Some 100 confirmed rocky exoplanets are so online, investigating Earth cousins will illu- Springer, Cham, Switzerland, https://doi­ .org/​ 10­ .1007/​ 978-­ 3-​­ 319​­ ​ -55333-­ 7_15.​­ close to their stars that they have surface seas minate the processes underpinning habit- Zolotov, M. (2018), Chemical weathering on Venus, in Oxford of very low viscosity magma. The chemical ability in our galaxy and reveal much that is Research Encyclopedia of Planetary Science, edited by P. Read evolution of these ­long-​­lived magma seas is relevant for understanding Earth twins. et al., Oxford Univ. Press, Oxford, U.K., https://doi­ .org/​ 10­ ​ .1093/acrefore/­ 9780190647926­ .013​ .146.​ affected by fractional vaporization, in which From sub-­ ​­Neptunes, for example, we can more volatile materials rise into the atmo- learn about volatile delivery processes. From sphere and can be relocated to the planet’s hot, rocky planets, we can learn about darkside or lost to space [e.g., Léger et al., ­atmosphere-​­interior exchange and atmo- By Edwin Kite (kite​@uchicago​.edu), University 2011; Norris and Wood, 2017], and perhaps by spheric loss processes. From water worlds, we of Chicago, Chicago, Ill.; Laura Kreidberg, Max exchange with underlying solid rock. can learn about nutrient supplies in exoplan- Planck Institute for Astrophysics, Heidelberg, Magma planets usually have low albedos, etary oceans and the potential habitability of Germany; Laura Schaefer, Stanford University, reflecting relatively little light from their these exotic environments. From disintegrat- Stanford, Calif.; Razvan Caracas, École Normale surfaces. However, some of these planets ing planets, we can learn about the interior Supérieure de Lyon, Lyon, France; and Marc appear to be highly reflective, perhaps composition of rocky bodies. Hirschmann, University of Minnesota, Twin Cit- because their surfaces are distilled into a Laboratory studies of processes occurring ies, Minneapolis kind of ceramic rich in calcium and alumi- on these worlds require only repurposing and num. One magma planet’s thermal signature enhancing existing experimental facilities, u Read the article at bit.ly/Eos-Earth​ has been observed to vary from month to rather than investing in entire new facilities. -cousins

SCIENCE NEWS BY AGU // Eos.org 19 By Damond Benningfield

The bright clutter of individual discoveries can overshadow some fascinating research, from necroplanetology to rogue planets to the intimacy of alphanumeric nomenclature.

hen astronomers gathered to reveal “new planets” at a press conference in January 1996, the world paid attention. Hundreds of journalists and fellow astronomers packed the meet- Wing room, where presenters confirmed the identity of one exoplanet and reported the discovery of two others—the first planets known to orbit other ­Sun-​ ­like stars. The story made the front pages of major newspapers (“Life in Space? 2 New Planets Raise Thoughts,” wrote the New York Times), appeared in magazines (including a Time cover story), and aired

In this illustration, radiation from a white dwarf is blasting an orbiting planetesimal to bits. The emerging field of necroplanetology is studying such exoplanetary debris. Credit: ­Harvard-​­Smithsonian Center for Astrophysics/Mark A. Garlick

20 Eos // AUGUST 2021 SCIENCE NEWS BY AGU // Eos.org 21 composition. (Astronomers have used the same technique to measure the atmo- spheres of planets transiting much larger main sequence stars, which are in the prime of life.) “What we started finding first was not whole planets but planetary debris,” Redfield said. In particular, using early observations from the K2 mission of the ­planet-​­hunting Kepler space telescope, they found WD 1145+017, a white dwarf about 570 ­light-​ ­years from Earth. The star’s light dipped several times in a pattern that repeated itself every few hours. The researchers con- cluded that they were seeing the debris of a planet that had been shredded by its star’s gravity—probably chunks or piles of rock surrounded by clouds of dust. Observations with large ­ground-​­based ­An artist’s rendering of OGLE-​­2005-​­BLG-​­390L b, which was discovered through gravitational microlensing. It is telescopes revealed calcium, magnesium, one of the most remote exoplanets yet seen, at a distance of about 20,000 ­light-​­years. Credit: ESO iron, and other heavy elements in the white dwarf’s spectrum. Such heavy elements should quickly sink toward the core of a white dwarf, where they wouldn’t be on television news (including CNN) soon “We’ve discovered a lot of weird things,” detected. Their discovery suggested that the after. said Laura Mayorga, an exoplanet researcher elements had been deposited quite recently, A quarter of a century later, exoplanets still and postdoctoral fellow at the Johns Hopkins as rubble from a disrupted planet (or plan- generate headlines—sometimes. With the University Applied Physics Laboratory (APL). ets) spiraled onto the white dwarf’s surface. number of confirmed planets well beyond “When we first started studying exoplanets, “All those clues made it clear that planets 4,000 and more being added to the list we found that they got stranger and stranger. can exist around white dwarfs,” said Red- almost weekly, however, a sort of exoplanet They put all of our understanding to the field. “They can be destroyed by white fatigue has set in. Only the most spectacular test.… Finding something new throws dwarfs as well. The tidal forces are quite discoveries show up in our daily newsfeeds: everything up in the air, and it has to reset- extreme, so they can break apart and grind potentially habitable planets, for example, or tle. That makes this a really exciting time.” up a planet.… As that material accretes onto “extreme” worlds—those that are especially the white dwarf, we’re actually learning hot or young or blue or close to our solar sys- Death of a Planet about the innards of the planets.” tem. Although it sounds like something from a Such a planet may have been born far from Yet some of the topics in the penumbra of Syfy channel original movie, necroplanetol- its host star and migrated close enough to be exoplanet discussions are just as fascinating ogy is the newest branch of exoplanet stud- destroyed. Astronomers know that such as those in the spotlight. They remain in the ies—a novelty that involves intrinsically rare migrations are possible because they have shadows in part because they involve objects targets. The term was coined by Girish Duv- discovered a few hundred “hot Jupiters”: that are rare or that are difficult to find and vuri, then a student working with Seth Red- worlds as massive as the largest planet in the study with current technology. The recently field at Wesleyan University in Connecticut, in solar system but so close to their stars that named field of necroplanetology, for exam- a 2020 paper. “We’re proud of the name,” their upper atmospheres are heated to hun- ple, studies planets orbiting dead or dying said Redfield. “It’s a great way to describe the dreds or thousands of degrees. Some of these stars, providing the only direct look at the systems we’re studying. It has a small num- planets are being eroded by stellar radiation innards of exoplanets. Gravitational micro- ber of practitioners, but the larger community and winds, perhaps marking the beginning lensing allows astronomers to detect planets is just starting to look into this topic.” of the end for worlds that could be subjects at greater distances than once thought pos- The name was originally applied to the for future necroplanetologists. sible. Several groups of researchers are study of dead or dying planets around white developing instruments or small spacecraft dwarfs, which are the hot but dead cores of Stars That Take a Dip to look at Earth as an exoplanet analogue, once normal stars. A typical white dwarf is Despite expectations of a bounty of such showing us what our planet would look like at least 60% as massive as the Sun but only white dwarf systems, Redfield said, they to an astronomer many ­light-​­years away. about as big as Earth. The size of white seem to be rare. (A recent study found evi- And the International Astronomical Union dwarfs makes it easier to detect the remains dence of one intact giant planet around one (IAU) has begun the long process of bestow- of pulverized planets as they transit, pass- white dwarf.) Astronomers have found evi- ing proper names on exoplanets—a process ing across the face of the star and causing its dence of similar processes at work around that simply may not have had enough time brightness to dip a tiny bit. main sequence stars, though. to filter into the consciousness of either pro- Starlight filtering through an exoplanet’s The ­best-​­known example is KIC 8462852 fessional astronomers or the public. atmosphere during a transit would reveal its (also known as Boyajian’s Star), about 1,470

22 Eos // AUGUST 2021 ­light-​­years from Earth. Large, but irregular, dips were discovered in the brightness of the star, which is bigger, hotter, and brighter than the Sun. Possible explanations for the decrease included the panels of a “mega- structure” built by an advanced civilization orbiting the star—an idea (since abandoned) that generated plenty of headlines. Astronomers have discovered other examples of “dipper” stars as well. Edward Schmidt, a professor emeritus at the Uni- versity of ­Nebraska–​­Lincoln, reported 15 slow dippers, whose light varies over long timescales, in a study released in 2019. He said he plans to publish details on 17 more in an upcoming paper. The stars all have similar masses and temperatures, which suggests that their dipping patterns share a common explana- tion, Schmidt said. “It could be caused by This artist’s view shows a brilliant aurora on one of the planets of the pulsar PSR 1257+12, energized by the pul- disintegrating planets—that looks promis- sar itself (top left). The system’s other two confirmed planets also are in view. Credit: NASA/JPL-­ ​­Caltech ing so far.” He’s looking through published spectra of the stars to see whether their surfaces are polluted by the residue of plan- ets, which could solidify the idea. than a white dwarf. A pulsar is a rapidly Metzger and Ben Margalit, also of Colum- A couple of systems discovered by Kepler spinning neutron star, the collapsed core of bia, have suggested, for example, that the seem to add credence to the hypothesis. a massive star that exploded as a supernova. companion could be a white dwarf. The ­Kepler-​­1520b, for example, shows dips in As the neutron star spins, it emits pulses of extreme gravity of the neutron star tears the luminosity of up to 1.3%. A ­ground-​­based energy that form an extremely accurate white dwarf apart—perhaps in a matter of study found that the dimming is caused in clock. The gravitational tug of a companion seconds—and the debris forms a disk part by clouds of dust grains, providing alters the timing of the pulses a tiny bit, around the pulsar. Some of the material in “direct evidence in favor of this object being revealing the presence of an orbiting planet. the disk falls onto the neutron star while a ­low-​­mass disrupting planet,” according to The first identified pulsar planets orbit the outer edge of the disk expands and a 2015 paper. And ­K2-​­22, discovered in PSR B1257+12. Astronomers have since dis- cools. Solid material in those precincts may Kepler’s K2 mission, appears to be a disinte- covered a handful of others, but most condense to form solid bodies, which then grating planet more massive than Jupiter but searches have come up empty. An examina- merge to make planets. only 2.5 times the diameter of Earth. tion of more than a decade of observations The scenario would explain the frequency Another study suggested a slightly altered made by the North American Nanohertz of pulsar planets, which is roughly equal to explanation for Boyajian’s Star and other Observatory for Gravitational Waves the frequency of neutron ­star–​­white dwarf dippers: disintegrating exomoons. (NANOGrav), a project that is using pulsar binaries, Metzger said. It would not, how- Researchers suggested that one or more timing to hunt for gravitational waves, for ever, explain the birth of a pulsar planet moons could be snatched away as a planet example, found no evidence of planets that’s been discovered in a globular cluster, falls into its star. “The planet essentially around a set of 45 ­fast rotating pulsars. The where the density of stars is extremely high. hands its moons to the star—they’re search could have revealed planets as light “You’d have to invoke more exotic interac- orphaned exomoons,” said Brian Metzger, as the Moon in orbital periods of 1 week to tions,” which scientists are still trying to one of the study’s authors and a physicist at almost 5 years, said Erica Behrens, a gradu- model, he said. Columbia University and senior research ate student at the University of Virginia who scientist at the Flatiron Institute. conducted the study during an internship at A Rogues’ Gallery of Exoplanets Stellar radiation could be eroding the sur- the National Radio Astronomy Observatory. Although most exoplanets have been discov- viving moons, releasing solid grains of mate- “Since we’ve seen so few, it seems like ered through transits or radial velocity mea- rial that then form a clumpy disk around the they’re pretty rare,” Behrens said, which may surements, which detect a ­back-​­and-​­forth star. So the young field of necroplanetology explain why they’ve received so little atten- shift in the wavelengths of starlight caused may need a new subfield: necrolunarology. tion since the early discoveries. “They must by the pull of orbiting planets, a few strag- have formed after the star has blown up. No glers have been found through other meth- A Second Chance at Life planet that existed while the star was still liv- ods. Such methods are difficult to apply, or For some planets, though, the death of a ing would be able to survive the supernova.” they’re looking for objects or phenomena star isn’t necessarily the end—it may be the Theoretical work hints that instead of that are rare, so they’ve yielded far fewer beginning. The first confirmed exoplanets, supernova survivors, pulsar planets may be discoveries than the most favored methods. discovered 3 decades ago, orbit a pulsar, a “zombies,” born from the debris of com- Astrometry, for example, precisely mea- dead star whose composition is more exotic panion stars. sures a star’s position to detect tiny wobbles

SCIENCE NEWS BY AGU // Eos.org 23 This diagram shows how microlensing reveals a planet orbiting a star. Credit: NASA, ESA, and K. Sahu (STScI)

caused by the gravitational tug of orbiting nique is used on a larger scale to study gal- planets—a minimum of 5 times the mass of planets. Such measurements are hard to axies and quasars billions of ­light-​­years Jupiter, Penny said. “So far,” however, he make and have yielded only one or two dis- away.) explained, “the main results are that there coveries. However, astronomers expect The length and magnification of a lensing are not a lot of ­free-​­floating giant planets observations by the Gaia spacecraft, which event allow astronomers to calculate the out there,” with only a handful of confirmed is plotting the positions and motions of intervening object’s mass and, in the case of discoveries to date. more than 1 billion stars, to yield thousands a planet, its distance from its star. Astrono- Most rogues probably form from the disk of new ­Jupiter-​­sized exoplanets in relatively mers have measured ­planet-​­star separa- of material around a star, then escape. “It wide orbits, which would create a whole new tions of up to more than 10 astronomical could be an interaction between planets,” population for study. units (AU), which is far wider than with Penny said. “If you form a lot of planets in a The most successful of the lesser known other techniques. disk, the disk keeps order until it dissipates. techniques, however, has been gravitational Microlensing can reveal planets that are But once the damping effect of the disk is microlensing which has revealed more than thousands of light-­ ​­years away (the current gone, all hell breaks loose,” and gravita- 100 planets. “It’s very complementary to record holder, according to the NASA Exo- tional battles can sling planets into inter- other techniques,” said Matthew Penny, an planet Archive, is at 36,500 ­light-​­years, many stellar space. There may be billions of these astronomer at Louisiana State University. times farther than planets discovered with smaller castaway worlds. “You get an instant detection of some very other techniques). Microlensing allows Although three searches are dedicated to distant planets that would take decades to astronomers to study planets in regions of the finding planetary microlensing events, find with other techniques.” Milky Way well beyond our own stellar neigh- they’re restricted by daylight, clouds, and Gravitational microlensing relies on gen- borhood, including the central galactic bulge. the other disadvantages of looking at stars eral relativity, which posits that if a star or Perhaps most important, microlensing is from the ground. planet passes in front of a more distant star, the only technique that can reveal rogue As with astrometry discoveries and the the intervening object’s gravity bends and planets, which travel through the galaxy Gaia mission, though, a space telescope may magnifies the background star’s light, cre- alone, unmoored to any star. greatly expand the numbers of confirmed ating a double image. If the alignment is Rogues might form as stars do, from the exoplanets. The Nancy Grace Roman Space perfect, it creates a bright circle of light gravitational collapse of a cloud of gas and Telescope, which is scheduled for launch known as an Einstein ring. (The same tech- dust. That process would form only massive later in the decade, could find 1,400 bound

24 Eos // AUGUST 2021 exoplanets and 300 rogues during its life- ­thought-​­provoking discoveries, will gain time, Penny said. The telescope’s mirror their share of the spotlight. will be the same size as that of Hubble The three exoplanets discussed at the Space Telescope, but with a field of view January 1996 press conference, for example, ­100 ­times wider. That field of view will were designated 51 Pegasi b, 47 Ursae Majo- allow Roman to see a large area toward the ris b, and 70 Gamma Virginis b—the names galactic bulge—the preferred target for of the parent stars followed by the letter b. microlensing planet searches. Current Astronomers have used that naming plans call for it to scan the region six times scheme ever since, with extra planets in a for 72 days per session. system assigned the letters c, d, e, and so “It’s the ideal platform for doing micro- on, on the basis of the order of discovery. lensing because you can never predict when The system works well, although the a lensing event will occur, and planetary A rogue planet glides through the galaxy alone in names get a little confusing when the star events are very short,” Penny said. this artist’s impression. Credit: NASA/­JPL-​­Caltech has only a long catalog designation; no one’s going to be enchanted by 2MASS One Telescope, Many Exoplanet J21402931+1625183 A b, for example. And Studies such “telephone book” designations are Roman is expected to help with other exo- polarized light from an instrument that hardly going to appeal to the public, which planet studies as well. As a technology hitches a ride on a lunar orbiter or lander. regularly sees planets with names like demonstration, it will carry a coronagraph, “Measuring the linear polarization of a Tatooine and Vulcan and Gallifrey in movies which blocks the light of a star, allowing planet over a range of time yields a wealth and TV shows. astronomers to see the light of planets of information about atmospheric constitu- So the IAU has conducted two interna- directly. “It’ll try to get down to ­Jupiter-​­like ents and clouds, as well as surface features tional competitions that have produced exoplanets that are closer than Jupiter is like vegetation, water, ice, snow, or des- proper names for more than 140 exoplanets. now,” said Mayorga. “It might get as close erts,” said Dora Klindži´c, a member of the In the most recent project, 112 countries held as 1 AU for a ­Sun-​­like star.” mission team and a graduate student at individual contests, with each country pro- Current images of exoplanets, whether Delft University of Technology and Leiden posing the name for one planet and its star. from telescopes in space or on terra firma, Observatory. “By observing Earth from a “It was great to tap into the public imagi- generally cover a single pixel. To better distance where we can reasonably pretend nation,” said Eric Mamajek, cochair of the understand those pictures, scientists use the we are an outsider looking at the Earth, such naming campaign steering committee and planets of our solar system as exoplanet ana- as from the Moon, we can learn how a deputy chief scientist for NASA’s Exoplanet logues. In essence, they take the beautiful planet richly inhabited with life and vegeta- Exploration Program. “I was blown away by pictures of Earth and the other worlds that fill tion appears when observed from another the ones that made it through the cam- Instagram pages and squish them down to a faraway planet. In a way, we are looking at paign. The names all have stories.” pixel. “That sets a ground truth for the weird ourselves to know others.” Astronomers have been slow to adopt the things we find in the universe,” Mayorga Interstellar Probe could provide that type names, though. The names don’t show up in said. “It allows us to connect that ­disk-​ of understanding from an even more distant most of the major online catalogs, for ­integrated light to the underlying cloud bands perspective. The proposed spacecraft could example. “Those phone book names take on or continents or oceans. It’s the only place we travel up to 1,000 AU from the Sun to study the intimacy of a proper name for most can make that connection.” interstellar space and would look back astronomers,” said Redfield. “I know that Mayorga and colleagues used Cassini toward the planets of the solar system. HD 189733 b [an exoplanet he’s studied] is images snapped during a flyby of Jupiter as “Ten, 20, 30 years into the mission, we just a bunch of numbers, but for me it has one analogue. They saw how the planet’s would have observations of the solar system the power of a proper name. I call it ‘189.’ brightness and color changed as viewed from outside looking in, as if we were flip- We’re on a nickname basis.” under different Sun angles or as the Great ping the telescope and taking a look at a “I think it will be a long process,” said Red Spot rotated in and out of view. planetary system we do know,” said Michael Mamajek. “It may take a new generation— Several teams are developing missions or Paul, project manager for the mission study people who grew up reading these names in instruments that would use Earth as an exo- at APL. “Tying that with in situ data we have textbooks.” planet analogue. Mayorga, for example, is for Mercury, Venus, Mars, Earth, Jupiter, Perhaps that new generation will recognize involved with a concept known as Earth tran- Saturn will better inform the models we the first exoplanet confirmed around a ­Sun-​ sit observer, a proposed CubeSat mission that have of other planetary systems.” ­like star not as 51 Pegasi b but as Dimidium or would watch Earth from L2, a gravitationally the first pulsar planets not as PSR B1257+12 b stable point in space roughly 1.5 million kilo- No Tatooines Here and c but as Draugr and Poltergeist. meters beyond Earth. Transits of the Sun Give an object a good name, and people are would reveal the composition of our planet’s likely to pay attention. “The fact that [Boy- Author Information atmosphere, including its many “biomark- ajian’s Star] has this special name means Damond Benningfield (damond5916@att​ .net),​ ers,” such as oxygen, ozone, and methane. that there aren’t many other objects like it,” Science Writer Another mission, LOUPE (Lunar Observa- said Redfield. Perhaps with catchier names, tory for Unresolved Polarimetry of Earth), the “unsung” planets and techniques, u Read the article at bit.ly/ would monitor Earth in both optical and which can produce some of the most Eos-rogue-exoplanets

SCIENCE NEWS BY AGU // Eos.org 25 Opposite Page: XXXXXX; This Page: Top Right: XXXX Top XXXXXX; This Page: Opposite Page:

26 Eos // AUGUST 2021 Opposite Page: XXXXXX; This Page: Top Right: XXXX OVERTURE To OVERTURE ExoplanetS about to rise on the on rise to about Telescope. Let’s see Let’s Telescope. what’s for store in golden mirrorsallowittocollectabroad rangeofinfrared James Space Webb The JamesWebb SpaceTelescope’s iconichexagonal light, perfectforuncoveringthesecrets ofexoplanets. BY Kimberly M. S. Cartier M. Kimberly BY rdt NS/hi Gn, CB . (­bit​.ly/​­ccby2-0) CC BY 2.0 Gunn, NASA/Chris Credit: its opening act. opening its SCIENCE NEWSBY AGU The curtainThe is

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he ­long-​­awaited launch of the want to look at first. In 2020 they submitted ence experiments have been carefully and James Webb Space Telescope their proposals to the telescope’s science equitably judged.” ( JWST) is finally in sight. Astron- team, and the selections for JWST’s first Andrew Vanderburg, an astronomer at omers around the world are observing cycle were announced in March. the University of ­Wisconsin–​­Madison, anticipating the wealth of infor- (An observing cycle is 1 year, or 8,760 hours, added, “It’s awesome that the [dual anony- mation the flagship will gather of observing time.) More than 20% of JWST’s mous] peer review—where the reviewers on everything from the oldest galaxies in time during its first observing cycle will be don’t know who wrote the proposals, and the universe to the birthplaces of stars and dedicated to understanding exoplanets. vice versa—makes it possible for young sci- Tplanets. The unifying theme across the exoplanet entists with good ideas to be awarded time “It really is a Swiss army knife telescope observing programs? “One word: diversity,” on the world’s most powerful observatory with a huge range of applications,” said said Stefan Pelletier, an astronomy doctoral from day one.” Elisabeth Matthews, an astronomer at student at Université de Montréal. “All Observatoire de Genève in Switzerland. bases are being covered in terms of science Prologue: A Shakedown Cruise JWST, built by a team of more than 1,200 cases as well as instrument and observing JWST promises to be a game changer for people from 14 countries, will collect infra- configurations.” understanding how and what types of plan- red (IR) light across a broad range of wave- The list of principal investigators (PIs) ets form and what makes them habitable, lengths. That makes it ideally suited to and coinvestigators on the accepted pro- but for this first cycle it’s unknown how the studying exoplanets, which bury most of grams is also more diverse across many axes telescope’s performance will measure up to their secrets deep in the infrared spectrum. of identity than space telescope programs expectations. “The reviewers very much In this way, among many others, JWST will have been in the past. Compared with a wanted a robust ‘shakedown cruise,’” said build on the legacies of the Hubble and recent round of Hubble proposals, a higher Peter Gao, an exoplanet scientist at the Uni- Spitzer space telescopes, both of which percentage of PIs who are women and also versity of California, Santa Cruz. “Several astronomers have used to make revolution- PIs who are graduate students will make the proposals focused on new and interesting ary leaps in our understanding of distant first JWST observations. observing methods and science cases that worlds, although neither telescope was It’s a testament to the hard work by the are sure to be the testing grounds for simi- designed to do so. JWST’s instruments, on team at the Space Telescope Science Insti- lar, larger, and more elaborate proposals in the other hand, were designed with exo- tute, Matthews said, “both in making sure the next cycles.” planets in mind. [members of] the exoplanet community are The selected exoplanet observations tend The observatory is scheduled to launch by able to understand the telescope and design to stay well within the telescope’s expected the end of this year, and exoplanet scien- good science experiments for it and also in limitations. “JWST time is very precious, so tists have long been planning what they ensuring that the proposals for these sci- for the first cycle it is understandable that emphasis was put on programs that are ‘safe’ in that they are almost guaranteed to generate good results,” said Alexis Brande- ker, an astronomer at Stockholm Univer- sity. Some observations might be “risky” in that the scientists aren’t sure what they’ll find, but if they do find something, they’ll get a good look at it. On the science side, there’s variety both in the types of planets targeted for observations and in the types of observations being made. “These include the measurement of mineral cloud spectral features as a way to probe the composition of exoplanet clouds, exploring asymmetries in the dawn and dusk limbs of exoplanets during transits, eclipse mapping, and getting a sense of which rocky exoplan- ets host atmospheres,” Gao said. And on the target side, “there is a nice balance between some of the first exoplan- ets to be characterized, like HD 189733 b, and weird exoplanets whose observations were difficult to interpret, like 55 Cancri e,” said Lisa Đăng, a physics graduate student at McGill University in Montreal. Instead of making limited observations of a wide range In 2007, astronomers used the Spitzer Space Telescope to create the first global temperature of an exoplanet, of planets, most of the selected exoplanet the hot Jupiter HD 189733 b. With JWST, astronomers plan to make a map of this planet’s hot spots (yellow) and programs seek to observe one or a few plan- cold spots (blue) not just in 2D, but also in 3D. Credit: NASA/­JPL-​­Caltech/​H. Knutson (Harvard-Smithsonian cfa) ets in great detail.

28 Eos // AUGUST 2021 The surface of 55 Cancri e is probably molten, as seen in this artist’s illustration. Astronomers will use JWST to better understand how the surface heats up. Credit: ESA/Hubble, M. Kornmesser, CC BY 4.0 (­bit​.­ly/​­ccby4-0)

Lights Up on a Familiar Scene will make a 3D map of the planet’s glowing including the ­Earth-​­sized lava world In this first observing cycle, “we are going dayside to study its wind and temperature 55 Cancri e. Brandeker’s program will exam- after a lot of known exoplanets that we have patterns, “which tells us a great deal about ine changes in light when the glowing, mol- observed in the past, so there aren’t many the physical processes taking place in the ten planet passes behind its star. “We hope unexplored targets,” Đăng said. “This atmosphere.” to see if consecutive eclipses show the same makes absolute sense since it will be the first time we are going to use these instru- ments in space and we don’t really know what challenges we will have to deal with JWST will build on the legacies of the yet.” “There are some really interesting plan- Hubble and Spitzer space telescopes, ets…that we already have tantalizing glimpses of from Hubble and Spitzer data,” said Hannah Wakeford, an astrophysicist at both of which astronomers have used the University of Bristol in the United King- dom. Wakeford, for example, will be target- to make revolutionary leaps in our ing a well-­ ​­studied, but still mysterious, hot Jupiter, HD 209458 b. “The data we cur- understanding of distant worlds. rently have from Hubble tell us there is something in this atmosphere, and my pro- gram aims to show that it is clouds made Néstor Espinoza’s target is hot Jupiter or different faces of the planet,” he said. from magnesium silicates (glass),” she said. ­WASP-63 b and, more specifically, its sunrise Planets that orbit close to their stars are Tiffany Kataria, a planetary scientist at and sunset. The program “aims to try to assumed to be tidally locked, having the NASA Jet Propulsion Laboratory in Pasa- detect, for the first time, the infrared atmo- same hemisphere always facing the star. If dena, Calif., is part of one of the five pro- spheric signatures of the morning and eve- 55 Cancri e rotates faster or slower than it grams studying HD 189733b, a hot Jupiter so ning limbs of a hot gas giant exoplanet…. It orbits, “this assumption, often taken for normal that it’s called canonical. “This goes in the direction of exploring atmospheric granted, can be questioned also for other planet was one of the first exoplanets whose structure of these distant exoplanets in 3D.” planets. This in turn has major implications atmosphere was observed with the Spitzer Espinoza is an astronomer at the Space Tele- for how planets are heated, i.e., one side and Hubble space telescopes, yet there is scope Science Institute in Baltimore, Md. versus all sides.” still much we don’t know about the proper- Plenty of smaller planets reside among Another old favorite is the ­sub-​­Neptune ties of its atmosphere,” she said. Kataria the old favorites that JWST will study, GJ 1214 b, the target of one of Eliza Kemp-

SCIENCE NEWS BY AGU // Eos.org 29 The flash heating that HD 80606 b experiences once every 111 days likely creates intense storms and unexpected weather patterns, which JWST will monitor. These com- puter models of those weather patterns are based on Spitzer data taken during a 2007 flash heating event. (Blue represents colder bulk atmosphere, and red represents warmer winds.) Credit: NASA/­JPL-​­Caltech/​G. Laughlin (UCO/Lick Observatory)

ton’s observing programs. “Through a com- data taken previously with facilities like like [carbon dioxide, water, and ozone] in bination of ­mid-IR transmission spectros- Hubble and Spitzer.” those atmospheres. This would be an copy, plus thermal emission and secondary Newest among the old favorites soon to important step in the search for traces of eclipse observations, we aim to get a clearer be studied by JWST is the ­TRAPPIST-1 sys- life outside the solar system.” picture of the atmospheric composition and tem, which excited astronomers and the “JWST has a small chance of finding bio- aerosol properties of this enigmatic world,” public alike when it was discovered to have signatures on ­TRAPPIST-1 planets,” said she said. seven possibly rocky ­Earth-​­sized planets. Michael Zhang, “but a very good chance of “The overlap with existing observations A grand total of eight different programs telling us which molecules dominate the is not a main motivator because we expect will look at these planets’ atmospheric atmosphere and whether there are clouds.” JWST to perform so much better than exist- properties. “With this program,” said Olivia Zhang is an astronomy graduate student at ing facilities,” said Kempton, an exoplanet Lim, an astronomy doctoral student at Uni- the California Institute of Technology in astronomer at the University of Maryland in versité de Montreal and PI for the program, Pasadena. College Park. “But it will certainly be reas- “we are hoping to determine whether the suring to see that the JWST data do agree planets have an atmosphere or not, at the Planetary Plot Twists with prior observations, and the level of very least, and if they do host atmospheres, Some exoplanets just don’t fit inside the box agreement will help us to contextualize all we wish to detect the presence of molecules as neatly as other exoplanets do, and astron-

30 Eos // AUGUST 2021 omers are really hoping that JWST will help them understand why that is. Kataria leads the program to study one of these oddballs, HD 80606 b. “HD 80606 b is an extreme hot Jupiter, and that’s saying something, given that hot Jupiters are pretty extreme to begin with!” Kataria said. “This ­Jupiter-​­sized exoplanet is on a highly eccentric, or elliptical, orbit and experiences a factor of greater than 800 variation in flux, or heating, throughout its ­111-​­day orbit.” “Most of the time it spends at relatively temperate distances,” Brandeker added, “but once every 111 days it swooshes very closely by the star in a few days so gets ‘flash heated.’” Studying HD 80606 b’s atmosphere as it heats and cools “will really help us examine the pure physics behind atmospheric energy transport, which is important for all worlds,” Wakeford said. Kataria is also a coinvestigator on a pro- gram to make a 3D atmospheric map of a dif- ferent oddity, WASP-121 b,­ a gas giant so hot The small rocky planet LHS 3844 b depicted in this illustration has been confirmed to have no atmosphere, so that it bleeds heavy metals into space and JWST will be able to study its surface composition. Credit: NASA/­JPL-​­Caltech/​R. Hurt, IPAC orbits so close to its star that it’s shaped like a football. ­WASP-121 b is one example of a “super-­ ​­puff” planet: These planets are roughly the size of Jupiter but far less mas- M Dwarfs’ Breathtaking Aria universe. There are tons of these small sive, which makes their density closer to that M dwarf stars are the smallest and most planets around small stars”— more than of cotton candy. Pelletier will be looking at common stars in the universe, and astrono- 1,500 are known so far—“but they experi- ence more ­high-energy​­ radiation over their lifetimes, so it’s not known whether they can keep their atmospheres. No atmosphere “JWST has a small chance of fiFInding [is] bad news for life!” Both of Kreidberg’s observing programs biosignatures on TRAPPIST-1 planets …but will target rocky planets around M dwarfs. “One of the planets [LHS 3844 b] is already a very good chance of telling us which known to not have an atmosphere, so the goal of this program is to study the planet’s molecules dominate the atmosphere and surface composition—what type of rock it’s made of—and search for any hints of volca- nic activity, which could produce trace whether there are clouds.” amounts of sulfur dioxide.” Kreidberg is also looking at ­TRAPPIST-1 c, another super-­ puff,​­ WASP-127 b.­ “Our hope mers have found that they host plenty of “which is very close to Venus in tempera- is to gain a better understanding of the carbon planets. Rocky habitable planets around ture. For that planet, I’m searching for budget on a planet vastly different from any- these stars are easier to find using the two absorption from carbon dioxide, to test thing we have in our solar system,” he said. most prevalent methods—transits and whether the planet has a thick, ­Venus-​­like What’s the most important thing to learn radial velocity—but whether those planets atmosphere or whether the atmosphere has about ­super-​­puff planets? “Basically any- can host atmospheres is still debated. been lost.” thing!” according to Gao, whose program “I think the Cycle 1 observations will “While we have made many models of will target ­super-​­puff Kepler-51 b.­ “All pre- teach us a ton about whether rocky planets atmospheric loss for small planets,” Gao vious attempts at characterizing ­super-​­puff around M dwarfs can keep their atmo- said, “this will be our first real test of these atmospheres have yielded featureless spec- spheres,” said Laura Kreidberg, director of theories. Will we find out that most charac- tra and therefore very little information. If research into the atmospheric physics of terizable rocky planets don’t actually have our observation is anything but a flat line, exoplanets at the Max Planck Institute for atmospheres and that our modeling efforts then we will have learned so much more than Astronomy in Heidelberg, Germany. “This for their climates and habitability are futile? what we now know about these mysterious is one of the most fundamental questions Or will we see a much more diverse set of objects. It really is a ­fact-​­finding mission.” about where life is most likely to arise in the atmospheric states? The results of these

SCIENCE NEWS BY AGU // Eos.org 31 studies will be interesting and informative exciting to me because it will provide us so, are they carbon dioxide, oxygen, or for future cycles regardless of what we find.” with a systematic survey of a class of planets exotic metal atmospheres made of sodium that is not present in our solar system and and silicon oxide?” ­Small-​­Planet Showstoppers was not readily observable with previous One of Espinoza’s programs will focus on About half of JWST’s ­exoplanet-​­specific facilities,” Kempton said. “The potential for ­super-​­Earth ­K2-141 b, a planet only slightly observing time will be dedicated to studying this program to unlock greater insight into larger and more massive than Earth but much, much hotter. “Depending on the properties of this exoplanet like the pres- ence or not of an atmosphere, the flux “This planet orbits close enough to the change during its orbit around the star should give rise to very different signals, white dwarf that it could not have which will enable us to infer what this exo- planet’s exterior is made of,” said Espinoza. originally orbited there before the If ­K2-141 b does have an atmosphere, it might not be the one it started with. Lisa Đăng aims to find out. Rocky planets as hot star’s death. So how did it get there?” as that one “are thought to have lost any primordial atmosphere but, instead, could worlds smaller than Neptune. “This tells me the atmospheres of small planets is quite sustain a thin rock vapor atmosphere [that] without a doubt that the community is high.” outgasses from the mantle,” she said. Does overwhelmingly interested in the little “These planets are so small that they’re the atmosphere stick around or rain back guys,” Gao said. These planets might be beyond the reach of current technology, so down? “With our observations we are hop- rocky (if they’re small enough) or could anything JWST discovers will be a big ing to detect molecular signatures of the have a ­rock-​­ice core and a thick atmo- improvement on what we know,” Zhang atmospheric constituents and also obtain a sphere. said. “For small planets like GJ 367 b, my map of the planet’s atmosphere and sur- “The large program on ­sub-​­Neptune and target, and 55 Cancri e, we basically don’t face.” ­super-​­Earth atmospheres led by Natasha know anything, so we’ll learn the first thing Batalha and Johanna Teske is especially about them. Do they have atmospheres? If Ballad of Planets and Disks JWST should build upon discoveries made not only by space telescopes like Hubble and Spitzer but also by ­ground-​­based observa- tories like the Atacama Large Millimeter/ submillimeter Array (ALMA). These obser- vations will probe the birthplaces of plan- ets: the disks of dust and gas around young stars. “Over the last decade, we’ve gotten gorgeous images from the ALMA interfer- ometer in Chile and have seen loads of ­fine-​ ­scale structure, tracing pebbles in ­planet-​ ­forming disks,” said Ilse Cleeves, an astronomer at the University of Virginia in Charlottesville. “Some of the structures likely trace planets in formation, and so it’ll be very exciting to see what JWST uncovers, both in terms of patterns in the disk and perhaps even the drivers—protoplanets— themselves!” Matthews added that “if JWST is able to successfully detect planets in these disks, it will be an important confirmation of our understanding of how planets interact with disks.” If no planets appear in the disks, astronomers will have to rethink how, and whether, planets shape disks. Cleeves will be studying ­planet-​­forming disks to understand how they give rise to Small planets all start from a collection of dust and gas. How much material a future planet starts with deter- habitable planets. “How common are hab- mines how much additional gas it can attract and how much of that gas it will keep when it heats up. Planets itable planets? Availability of water is a that end with a large gaseous envelope are termed mini-Neptunes, and those with only a small amount of gas natural place to start, but we don’t have are deemed super-Earths. Credit: NASA/Ames Research Center/­JPL-​­Caltech/​­R. Hurt great observational constraints on how

32 Eos // AUGUST 2021 much water is present or the distribution of water in disks. We are looking forward to mapping out water ice in a nearby disk that happens to be posing in front of a host of background stars.” If a star’s light passes through a part of the disk that has ice, the ice will imprint a spectroscopic signal on the light. With so many back- ground stars, Cleeves said, they’ll be able to say not just whether ice is present, but also where. The makings of a world well suited for life go beyond the presence of water, how- ever, and Melissa McClure’s three observ- ing programs will look for them. We’ll “trace how the elemental building blocks of life—like carbon, hydrogen, oxygen, nitrogen, and sulfur—evolve between molecular clouds, where they freeze out on dust grains as ices, and protoplanetary disks, where these ices are incorporated into forming planetesimals and, ulti- mately, planets,” she said. “I think that within a few years we will have an under- standing of how much water terrestrial planets typically have and whether they inherited that water from their birth loca- tions in their disks or if cometary delivery was necessary.” McClure is an assistant professor and a Veni Laureate at Leiden Observatory in the Netherlands. A perhaps underrecognized component of JWST’s observing capabilities is the corona- graph that will allow direct imaging of exo- planet systems, meaning that the telescope will see light emitted by the planet itself. Coupled with JWST’s infrared capabilities, A few of the first observations with JWST will seek to map out how planet-forming disks distribute their water the telescope will be able to observe planets and other materials that are essential for life. This artist’s illustration shows where water ice may exist in a much older and colder than is currently ­planet-​­forming disk. Credit: A. Angelich (NRAO/AUI/NSF)/ALMA (ESO/NAOJ/NRAO), CC BY 4.0 (­bit​.­ly/​­ccby4-0) possible. That’s Matthews’s aim. “Eps Indi Ab is similar in age to the solar system and is similarly far from its star as Jupiter is from the Sun. Because JWST is able to image Bridge to Act II really looking forward to the first couple of much further into the infrared than ­Earth-​ Once the “shakedown cruise” is complete, years with JWST, grappling with the data ­based telescopes and because old planets Hannah Wakeford would like to see JWST and finding those unexpected puzzles.” are brighter at these very long wavelengths, used to study more worlds the size of Espinoza agreed. “I’m almost convinced our project provides a unique opportunity to ­Jupiter, Saturn,­ and ­Neptune. “There is so features will show up in the data that we will study a truly ­Jupiter-​­like planet outside the much we can learn that we can’t even get perhaps not be able to explain right away,” solar system,” she said. from our own solar system giant planets,” he said. “As such, the very first exoplanetary Sometimes planets survive their star’s she said, “so it is, in my opinion, a low-­ ​­risk, observations to be made by JWST are going to demise, as is the case of WD 1856+534 b, a ­high-​­reward scenario.” be a big jump into the known unknown…. As gas giant planet that orbits the slowly cool- On Vanderburg’s wish list: “Disintegrat- the title of an album of one of my favorite ing corpse of a star, also known as a white ing planets. These will be great probes of rock bands would say, ‘Expect the unex- dwarf. In this case, the planet’s survival the interior compositions of planets, so I pected.’” presents a puzzle. “This planet orbits close hope we will get observations of them in the enough to the white dwarf that it could not future.” Author Information have originally orbited there before the Cleeves called the first cycle “a great Kimberly M. S. Cartier (@AstroKimCartier), star’s death. So how did it get there?” asked place to start. I have a feeling, though, that Staff Writer Andrew Vanderburg, whose program will the most interesting next projects are those target this system. that we haven’t anticipated yet, so I’m uRead the article at bit.ly/Eos-JWST

SCIENCE NEWS BY AGU // Eos.org 33 By Kate Evans

An artist’s concept of what exoplanet Kepler-1649 c could look like. The planet is similar in size to Earth and exists in its red dwarf star’s “habitable zone,” where liquid water could exist on its surface. Credit: NASA/Ames Research Center/Daniel Rutter

34 Eos // AUGUST 2021 Clouds make climate modeling on Earth difficult. Identifying—and even defining—atmospheric phenomena on other planets is the next big exoplanet challenge.

SCIENCE NEWS BY AGU // Eos.org 35 he first time scientists snow even mean in the context of the uni- measured the atmosphere verse. of an exoplanet—a planet “Clouds are everywhere,” said Laura outside our solar system— Kreidberg, an astronomer at the Max Planck they found something Institute for Astronomy in Germany. “And unexpected in the signal. to have any hope of understanding what’s It was 2001, and the Hubble Space Telescope going on in [exoplanet] atmospheres, we Twas trained on HD 209458 b, a recently dis- have to understand the clouds.” covered gas giant roughly the size of Jupiter. When astronomers looked for the pres- Mushballs and Methane Lakes ence of sodium in light waves shining The trouble is, clouds are complicated. Even through the planet’s atmosphere as it on Earth, clouds are difficult to model (one crossed in front of its star, there was a lot reason weather forecasts can still lack accu- less of it than they racy.) Their complexity arises partly because thought there they are simultaneously very small and very would be, said large: made up of microscopic water drop- Hannah Wakeford, lets yet so vast they can cover more than a lecturer in astro- two thirds of Earth’s surface. Another rea- physics at the Uni- son is that there are so many kinds of versity of Bristol in clouds, and they behave in complex ways, the United King- explained atmospheric physicist David Crisp dom. “From the at the Jet Propulsion Laboratory, California very first mea- Institute of Technology. surement of an Clouds are “ubiquitous; they can form in exoplanet atmo- many different kinds of environments, and sphere, there was there are many processes associated with evidence that their formation,” Crisp said. something else And they’re not made only of water, was happening, either. Most cloud particles start growing on something else condensation nuclei—a speck of dust or a was there blocking grain of salt. And although most earthly the light.” cloud droplets are spherical and liquid, The most com- those that make up cirrus clouds are hexag- pelling theory for onal ice crystals. what that some- Clouds can frustrate scientists’ ability to thing could be? see clearly, whether they are gazing at the Massive banks of heavens from the ground or peering back at dark, hot clouds. Earth from space. In the 1980s, Crisp “Clouds are essen- helped build the camera in the Hubble On Earth, clouds take many forms, like these cirrus tially liquid or Space Telescope and now leads a NASA and stratocumulus clouds. Their variety and ubiquity solid droplets or team that uses orbiting satellites to mea- make them difficult to account for in climate models. particles that are sure the dangerous levels of carbon dioxide Credit: NASA suspended in a accumulating in Earth’s atmosphere. “I’ve gaseous atmo- learned to hate clouds from both sides sphere,” said now,” he joked. Wakeford. But Clouds mess with models predicting because the planet is so hot—5 times hotter future climate change, he said, because they than Earth—those droplets couldn’t be simultaneously warm and cool the planet, made of water, as they are on Earth. depending in part on whether their droplets In the 2 decades since analyzing the are mainly liquid or mainly ice. In general, atmosphere of HD 209458 b, astronomers ­low-​­lying, mostly liquid clouds provide have discovered more than 4,000 exoplan- shade and reflect solar energy back into ets. Using spectroscopy, they have mea- space, whereas ­high-altitude,​­ frozen cirrus sured the atmospheres of more than 100 of clouds trap infrared radiation emitted by those objects, and it looks like many of Earth’s continents and oceans and intensify them are cloudy. The way those extrater- surface heating. This duality has long frus- restrial clouds behave and the exotic things trated exoplanet cloud watchers, too—sci- they could be made of—liquid sand, iron, entists scrutinize cloud signals to better even rubies—are stretching scientists’ understand how or whether clouds are ideas of what terms like clouds, rain, and heating the atmosphere below them.

36 Eos // AUGUST 2021 Scientists are still trying to understand whether, at a global level, those cooling and warming effects cancel each other out and how that balance could change in the future. (One recent study even suggested that at carbon dioxide levels of around 1,200 parts per million, global cloud cover could become unstable and dissipate, dramatically accel- erating warming.) Despite the uncertainties, we know a lot more about Earth’s clouds than we do about those on other planets and moons of our solar system. It was only in the 1970s, for instance, that scientists figured out that Venus is enveloped in clouds of sulfuric acid. “This stuff will strip paint—and just about anything else,” said Crisp. Space missions to Venus have dropped mass spectrometers into the planet’s atmosphere that, “even though sulfuric acid is not very nice to our mass spectrometers,” have managed to send back data about the chemical makeup and concentrations of several cloud layers. An artist’s impression of the gas giant ­HAT-P-7 b. Astronomers detected strong winds and catastrophic storms Jupiter’s atmosphere has been sampled and suspect that the clouds could be made of corundum, the mineral that forms rubies and sapphires. Credit: too, and has been found to contain swirling Mark Garlick/ University of Warwick ammonia clouds. Recent flybys of the tops of these clouds by NASA’s Juno mission identified mushballs—Jovian hailstones formed out of ­water-​­ammonia slush places, and they have complicated cli- enrobed in an ice crust—that fall through mates—quite as complicated as ours.” the planet’s atmosphere. On the way down, “We’ve dropped these mushballs collide with upward mov- A Lead Blanket or Gems and Jewels ing ice crystals and electrify the clouds, The challenges of analyzing extraterrestrial a few dozen causing ­shallow, high-​­altitude lightning clouds are magnified when it comes to exo- visible from space. planets. We can’t send a probe laden with probes into the Thanks to the Cassini spacecraft, we instruments to any of them or record know that the atmosphere on Titan, the detailed images of their surfaces. largest of Saturn’s moons, is largely made All we have is light, said Heather Knut- atmosphere of up of nitrogen, like Earth’s. There are sea- son—the light coming from a ­far-​­off star. sons, monsoons, and wild windstorms. But “We know there’s a planet in orbit around Venus. But you Titan’s mountains are made of solid ice, and it, and we can indirectly infer some basic instead of a water cycle, it has a hydrocar- things about that planet, but it’s really a know, if you bon cycle: On Titan, the rain, rivers, and sort of poor man’s camera,” said Knutson, lakes are made of methane and ethane. an astronomer at the California Institute of But many questions remain when it Technology measured Earth’s comes to solar system weather. For exam- When an exoplanet passes in front of its ple, we don’t know how deep into Jupiter star—an event called a transit—astronomers atmosphere with the mushballs fall before they evaporate can measure the way light passes through and rise again, said Wakeford. There are the planet’s atmosphere on its way to us. only a dozen mysterious ­long-​­chain hydrocarbons float- Measuring how opaque the atmosphere is at ing high in the atmosphere of Titan too. different wavelengths of light (transit spec- instruments, how “We have absolutely no idea how they got troscopy) offers clues to its composition. there; it’s baffling.” Kreidberg used an ­X-ray analogy to explain What knowledge we do have is drawn how it works: “Our bodies are opaque in much would you from the briefest of snapshots, added Crisp. optical light. If you shine a flashlight at a “We’ve dropped a few dozen probes into the person, you can’t see through them. But if know about the atmosphere of Venus. But you know, if you you look in the ­X-rays, you can see through measured Earth’s atmosphere with only a the skin, but not through the bones.” Earth?” dozen instruments, how much would you In the same way that our skin differs from know about the Earth? These planets are big our bones, molecules in planetary atmo-

SCIENCE NEWS BY AGU // Eos.org 37 spheres are opaque or transparent at differ- makes up the volcanic sand on some of ent wavelengths. “Whether it’s water or Earth’s beaches and is used in the production methane or oxygen or carbon dioxide, they of glass. On an even hotter planet like have distinct opacity at different wave- ­WASP-76b, which is estimated to reach lengths of light,” said Kreidberg. “So if the 2,400 K, clouds are likely made of liquid iron. planet looks a little bit bigger at a particular And the atmospheres of the hottest known wavelength, then we can work backward exoplanets—giant, 2,500+ K ultrahot Jupiters from that to try to infer what’s in its atmo- orbiting very close to their stars—are the sphere.” right temperature for clouds made of corun- But clouds get in the way of that process, dum, a crystalline form of aluminum oxide said Knutson. “If we’re going with the ­X-ray that forms rubies and sapphires on Earth. analogy, clouds are sort of like a lead blan- “These are quite literally the gems and ket over the planet. You see something that jewels that we have here on Earth forming looks very featureless.” clouds and lofted high into the atmospheres Still, on the basis of the planet’s average of ­Jupiter-​­sized worlds that are lit glowing atmospheric temperature—something from their star,” said Wakeford. She astronomers can estimate from the bright- remembered walking through the Hall of ness of the star and the planet’s distance Gems in London’s Natural History Museum from it—it’s possible to infer what those after learning this, trying to imagine the clouds are likely to be made of because of crystals molten and forming clouds. “It just the varying temperatures at which different blew my mind.” molecules condense from gas into liquid. And the vast Metallic Monsoons range of possible ­WASP-76 b made headlines in 2020 when a temperatures is team of European researchers published a something that paper suggesting it had not only clouds of distinguishes exo- iron but iron rain as well. planets from those Like our own Moon and many planets that in our solar sys- orbit very close to a star, ­WASP-76 b is tidally tem, said Nikku locked, meaning one side of the planet Madhusudhan, an always faces the star (dayside) and the other astrophysicist and always faces away (nightside). Researchers exoplanet scientist found evidence of iron atoms in the atmo- at the University sphere of ­WASP-76 b’s hotter dayside but of Cambridge. not on the cooler nightside, which they “Because of that argued meant that the iron must be con- vast range, you densing into liquid droplets as wind carries allow for a much the atoms around the planet. “We see the wider range of iron, and then we don’t see the iron. So it has chemical compo- to go somewhere, and the physical process sitions [than in that we expect is rain,” said Kreidberg, who the solar system]. was not involved in the study. “This is some A lot more chem- of the most convincing evidence I have ever istry can happen.” seen for exoplanet weather.” Here on Earth, But Caroline Morley, an astrophysicist at with an average the University of Texas at Austin, cautioned temperature of that the phenomenon could be more com- 290 K, clouds are plex. Recent studies, including one co­au- made mostly of thored by Kreidberg, have examined the water. The atmo- microphysics of how iron droplets form, spheres of some finding that the substance’s high surface An imagined movie poster for the exoplanet HD 189733 b, a exoplanets, tension means that it doesn’t easily con- ­cobalt-​­blue hot Jupiter with winds approaching 8,700 kilo- between 400 K and dense from a gas to a liquid. There might be meters per hour and rain of molten glass. Credit: NASA 900 K, are warm some other processes involved in enough to con- ­WASP-76 b’s iron phenomenon, Morley dense salts and said—perhaps the iron interacts with some sulfides into other chemicals in the planet’s atmosphere, clouds. At around 1,­400–​­2,000 K (a third as which helps it form a cloud. hot as the Sun), we would expect to see “Statistically, I believe that there are exo- clouds of molten silicates—the material that planets where it is raining right now,” she

38 Eos // AUGUST 2021 said. “But I think that we have not seen Madhusudhan. “We have to be open to the smoking gun evidence for rain on other fact that the complexity in nature may planets yet.” greatly surpass our imagination at the pres- “We see the iron, Crisp agreed. “Clouds we’ve detected. Rain ent time.” and snow have not yet been detected—but and then we I’d be surprised if they weren’t there. Those Peering into the Infrared are logical outcomes of the systems we see.” So far, everything we know about clouds on don’t see the exoplanets has been based on what Madhu- Metaphorical Meteorology sudhan calls indirect inference: “It’s a bit So when astronomers talk about possible more real than philosophical but a bit less iron. So it has to rain on exoplanets, is it really what we real than an actual observation.” But the would think of as rain? What do the con- launch of the international James Webb go somewhere, cepts of rain and clouds even mean in the Space Telescope ( JWST) near the end of this context of distant space? To some extent, year promises to give astronomers the and the physical it’s all a metaphor, said Wakeford. chance to make direct observations of exo- On Earth, the terms rain, clouds, and planet clouds for the first time. process that we snow all apply almost exclusively to one JWST will keep Earth between it and the substance: water. “Water is one of the most Sun and is designed to look at the longer expect is rain.” amazing materials in the universe,” Wake- wavelengths of infrared light. “Planets are ford said, but not all substances behave like easier to study in the infrared,” said Knut- water when experiencing differences in son. The telescope will make faraway objects pressure or temperature. “So when we look brighter than they do in visible light and frame these very alien clouds and rain and will be better able to detect molecules in exo- snow in that [­water-​­based] context, it puts planet atmospheres. It should also advance things in our minds that aren’t exactly what our understanding of alien weather. the physics is.” “When you go to midinfrared, the compo- For instance, words like snow and hail sition of a cloud droplet starts to matter— can be a bit misleading when you talk about the way that it scatters light is different for solid particles in an atmosphere that’s hot- different cloud species,” said Knutson. “So ter than a lava flow. “I tend to use rain we might, for the first time, directly measure instead of snow,” Wakeford said, “because what the clouds are made of.” snow to us evokes a temperature, a cold- Morley is leading a team that will use ness. Rain is something that can define JWST to examine a cold exoplanet called many different types of conditions, whereas WISE ­J085510.83−​­071442.5 to test for the snow for us is very much a cold thing. And presence of water ice clouds and see this is not what’s happening here on some whether they are changing as the planet of these planets that are so incredibly hot.” rotates, implying that there are storm sys- Still, Wakeford thinks a smattering of tems and weather. “That would give us real poetic license is justified to bring the public evidence, for the first time, that there’s along on the journey and capture people’s water ice forming in a planet outside of the imaginations. “If you start by saying, ‘It’s solar system,” Morley said. raining drops of glass on these planets’— Wakeford, meanwhile, will have a chance that’s a starting point. I can use that; I’ve to train the telescope on HD 209458 b, the very got [your attention] now. Then we can build first planet that 20 years ago was assumed to on that and get a deeper understanding.” have clouds of magnesium silicate. JWST will When it comes to actually doing the give her a chance to prove (or disprove) that research, though, scientists should be both assumption with direct measurements. circumspect and ­open-​­minded, said Madhu- Overall, “I think we think about clouds sudhan. Although it can sometimes help to more broadly than anybody has thought extrapolate from what we’re discovering about clouds in human history,” said Morley. about Earth’s clouds to these faraway plan- “And we’re just on the cusp of being able to ets, for instance, it’s important to remember get a huge amount of really detailed infor- that these worlds are so exotic that it’s pos- mation about those clouds. It’s a really sible there are processes going on in their exciting time to be in this field.” atmospheres that we haven’t even consid- ered. “The biggest mistake we could make is Author Information to try to simplify the complexity of exoplan- Kate Evans (@kate_g_evans), Science Writer etary systems just to fit a narrative.” We may go on to discover kinds of uRead the article at bit.ly/ weather we don’t even have words for, said Eos-exo-clouds

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40 Eos // AUGUST 2021 AGU NEWS

In Appreciation of AGU’s Outstanding Reviewers of 2020

GU Publications recognizes a number of outstanding reviewers for their A work in 2020, as selected by the edi- tors of each journal. Peer review is central to communicating and advancing science. While there have never been more ways to distribute ideas and research outputs, a robust peer review ensures that we maintain the highest integrity in our scientific discourse. The peer review process is organized by our journal editors, but every article decision relies on dedicated individuals who take time out from their own research to volunteer their time and expertise. The work of these reviewers ensures proper evaluation of thousands of articles each year. We are truly thankful for their efforts. As the uses for scientific literature have grown, so has the complexity of papers, which now typically include more authors bringing more techniques, data, simulations, and results. This increase in complexity has increased the challenge and role of reviewing. The outstanding reviewers listed here have provided ­in-depth​­ evaluations, often through multiple revisions, that greatly improved the final published papers. Their contributions which is up from the 16,700 submissions may be virtual) at Fall Meeting and other helped raise the quality of submissions received in 2019, and published more than meetings. received from around the world, providing 7,163, up from 7,000 articles in 2019. Many of Each reviewer also receives a discount on valuable feedback that elevates the promi- these submissions were reviewed multiple AGU and Wiley books. We will continue to nence of our journals to the high standards times—in all, 19,227 reviewers completed work with the Open Researcher and Contrib- aligned with the AGU tradition. 42,564 reviews in 2020 compared to the 39,368 utor Identification network (ORCID) to pro- reviews completed in 2019. vide official recognition of reviewers’ efforts, This increase has happened in the past year so that reviewers receive formal credit there. while each AGU journal worked to shorten the As of 5 May we have over 71,700 ORCIDs Every article decision relies time from submission to first decision and linked to GEMS user accounts as compared to publication or consistently maintained 59,962 at this time last year. on dedicated individuals who ­industry-​­leading standards. Several AGU journals regularly return first decisions Getting Your Feedback take time out from their own within 1 month of submission, and most oth- We are working to improve the peer review research to volunteer their ers do so now within 2 months. Reviewers process itself, using new online tools. We represent a key part of this improvement. We conducted a full survey in 2020, and we con- expertise. look back at 2020 here, but we have already tinue to provide a short questionnaire for seen that in 2021, during the pandemic and feedback after each review is completed. unrest, members of our amazing community We value your feedback, including ideas have continued to accept invitations to peer about how we can recognize your efforts even Many Reviewers: A Key Part ​ review article submissions. more, improve your experience, and increase of AGU Journals Editorials in each journal (some already your input on the science. While we note these few outstanding review- published, some upcoming) express our We look forward to hearing from you. If ers here, we also acknowledge the broad appreciation along with recognition lists. Our you’d like to respond directly, feel free to take efforts by many AGU reviewers in helping thanks are a small recognition of the large our survey. ensure the quality, timeliness, and reputation responsibility that reviewers bear in improv- Once again: Thanks! of AGU journals. We also welcome new and ing our science and its role in society. ­first-time​­ reviewers who have joined the fam- ily of integrity stewards and have been pro- Additional Thanks By Matt Giampoala (mgiampoala​@agu​.org), viding authors valuable evaluations. In 2020, We are working to highlight the valuable role Vice President, Publications, AGU; and Carol

dizain-stock.adobe.com AGU received more than 18,100 submissions, of reviewers through events (though they Frost, Chair, AGU Publications Committee

SCIENCE NEWS BY AGU // Eos.org 41 AGU NEWS

Sarah Aarons Franciscus Aben Eldert L. Advokaat Hoori Ajami Mark Allen Rose Cory JGR-Solid Earth editors Tectonics editors Water Resources Tectonics editors Geophysical Research JGR-Solid Earth Tectonics Research editors Tectonics Letters Water Resources Research

Grace Andrews Sylvain Barbot Roberto Basili Cameron Batchelor Timothy Bates Rose Cory Germán Prieto Tom Parsons Valerie Trouet JGR-Atmospheres editors Geophysical Research Geophysical Research AGU Advances Geophysical Research JGR-Atmospheres Letters Letters Letters

Sarah N. Bentley Tom G. Beucler Kevin Bladon Lina Boljka Pierre Boué Space Weather editors Journal of Advances in Water Resources Research JGR-Atmospheres editors JGR-Solid Earth editors Space Weather Modeling Earth Systems editors editors JGR-Atmospheres JGR-Solid Earth Journal of Advances in Modeling Water Resources Research Earth Systems (JAMES)

Ian Brooks Josephine Brown Manuela Brunner Ishi Buffam William Burt Hui Su Earth’s Future editors Water Resources Research JGR-Biogeosciences editors JGR-Oceans editors Geophysical Research Earth’s Future editors JGR-Biogeosciences JGR-Oceans Letters Water Resources Research

42 Eos // AUGUST 2021 AGU NEWS

Michael P. Byrne Miguel Angel Cabrera Harish Chandra Daniel Chavas Marie-Luce Chevalier Alessandra Giannini JGR-Oceans editors Sana Salous Suzana Camargo Tectonics editors Geophysical Research JGR-Oceans Radio Science Geophysical Research Tectonics Letters Letters

John Chiang Gabriele Chiogna Xinzhao Chu Hye-Yeong Chun Julia Cole Hui Su Water Resources Research Earth and Space Science JGR-Atmospheres editors Fabio Florindo Geophysical Research editors editors JGR-Atmospheres Reviews of Geophysics Letters Water Resources Research Earth and Space Science

Brian D. Collins Mathias Collins Kristen Corbosiero Kenneth Cummins Chimene Laure Daleu JGR-Earth Surface editors Water Resources Research Suzana Camargo JGR-Atmospheres editors Alessandra Giannini JGR-Earth Surface editors Geophysical Research JGR-Atmospheres Geophysical Research Water Resources Research Letters Letters

Francisco Delgado Meagan Eagle Jennifer Eccles David Evans Ian Faloona Christian Huber JGR-Biogeosciences editors JGR-Solid Earth editors Paleoceanography and Christopher Cappa Geophysical Research JGR-Biogeosciences JGR-Solid Earth Paleoclimatology editors Geophysical Research Letters Paleoceanography and Letters Paleoclimatology

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Michel Faure Grant Ferguson Christopher Fisher David D. Flagg Gwenn Flowers Tectonics editors Water Resources Research Geochemistry, Geophysics, Yu Gu JGR-Earth Surface editors Tectonics editors Geosystems editors Geophysical Research JGR-Earth Surface Water Resources Research Geochemistry, Geophysics, Letters Geosystems

Heather L. Ford Sven Frei Melodie French Martin Galis Rolando Garcia Paleoceanography and Water Resources Research JGR-Solid Earth editors JGR-Solid Earth editors JGR-Space Physics editors Paleoclimatology editors editors JGR-Solid Earth JGR-Solid Earth JGR-Space Physics Paleoceanography and Water Resources Research Paleoclimatology

Sarah N. Giddings Patricia M. Glibert Maxime Grandin Carlo Gualtieri Mike Hapgood JGR-Oceans editors JGR-Biogeosciences editors Mary Hudson Water Resources Research Andrew Yau JGR-Oceans JGR-Biogeosciences AGU Advances editors Geophysical Research Water Resources Research Letters

Elima Hassanzadeh Xiaogang He Nicholas G. Heavens Agnès Helmstetter Jonathan Herman Earth’s Future editors Valeriy Ivanov JGR-Planets editors JGR-Earth Surface editors Water Resources Research Earth’s Future Geophysical Research JGR-Planets JGR-Earth Surface editors Letters Water Resources Research

44 Eos // AUGUST 2021 AGU NEWS

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Wenxin Huai Chengxin Jiang Cathleen Jones McArthur Jones, Jr. Jason Kean Water Resources Research JGR-Solid Earth editors Water Resources Research JGR-Space Physics editors Harihar Rajaram editors JGR-Solid Earth editors JGR-Space Physics Geophysical Research Water Resources Research Water Resources Research Letters

Minseok Kim Vassili Kitsios Wouter J. M. Knoben Julian Koch Nicolas Kolodziejczyk Water Resources Research Journal of Advances in Water Resources Research Water Resources Research Kathleen Donohue editors Modeling Earth Systems editors editors editors Geophysical Research Water Resources Research Journal of Advances in Modeling Water Resources Research Water Resources Research Letters Earth Systems (JAMES)

Alexandra Konings Tobias Kukulka Evgeniy V. Kulakov Zachary M. Labe Phoebe Lam Valeriy Ivanov JGR-Oceans editors JGR-Solid Earth editors Harihar Rajaram JGR-Oceans editors Geophysical Research JGR-Oceans JGR-Solid Earth Geophysical Research JGR-Oceans Letters Letters

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Lifeng Luo Yali Luo Kristina A. Lynch Qianli Ma Yuxia Ma JGR-Atmospheres editors JGR-Atmospheres editors Andrew Yau Gang Lu Gabriel Filippelli JGR-Atmospheres JGR-Atmospheres Geophysical Research Geophysical Research GeoHealth Letters Letters

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Ali Mirchi Motoki Nagura Noboru Nakamura Yosio Nakamura Kaitlin Naughten Earth’s Future editors JGR-Oceans editors JGR-Atmospheres editors JGR-Planets editors JGR-Oceans editors Earth’s Future JGR-Oceans JGR-Atmospheres JGR-Planets JGR-Oceans

46 Eos // AUGUST 2021 AGU NEWS

Megan Newcombe Sharon E. Nicholson Hannes Nickisch Edwin Nissen Yoshiharu Omura Geochemistry, Geophysics, JGR-Atmospheres editors Earth and Space Science JGR-Solid Earth editors Andrew Yau Geosystems editors JGR-Atmospheres editors JGR-Solid Earth Geophysical Research Geochemistry, Geophysics, Earth and Space Science Letters Geosystems

Yuichi Otsuka Michel Parrot Eric Josef Ribeiro Parteli Thomas B. Phillips Daniel Evan Portner Space Weather editors and Sana Salous JGR-Earth Surface editors Tectonics editors Geochemistry, Geophysics, Gang Lu Radio Science JGR-Earth Surface Tectonics Geosystems editors Space Weather and Geochemistry, Geophysics, Geophysical Research Letters Geosystems

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48 Eos // AUGUST 2021 AGU NEWS

Bruce Tsurutani Natalie Umling Martijn van den Ende Elizabeth A. Vanacore Geraint Vaughan JGR-Space Physics editors Paleoceanography and JGR-Solid Earth editors JGR-Solid Earth editors Earth’s Future editors JGR-Space Physics Paleoclimatology editors JGR-Solid Earth JGR-Solid Earth Earth’s Future Paleoceanography and Paleoclimatology

Carolyn Voter Akiyoshi Wada Hailong Wang Xiaoyan Wang Nicholas Webb Water Resources Research JGR-Atmospheres editors JGR-Atmospheres editors Kaicun Wang Gabriel Filippelli editors JGR-Atmospheres JGR-Atmospheres Geophysical Research GeoHealth Water Resources Research Letters

Randy Williams Kimberly Wood Chenglai Wu Shiqing Xu Weixin Xu Geochemistry, Geophysics, Suzana Camargo JGR-Atmospheres editors JGR-Solid Earth editors JGR-Atmospheres editors Geosystems editors Geophysical Research JGR-Atmospheres JGR-Solid Earth JGR-Atmospheres Geochemistry, Geophysics, Letters Geosystems

Toshitsugu Yamazaki Jiachuan Yang Alissar Yehya Robert Yokelson Andrew Yool Monika Korte JGR-Atmospheres editors JGR-Solid Earth editors JGR-Atmospheres editors Global Biogeochemical Geophysical Research JGR-Atmospheres JGR-Solid Earth JGR-Atmospheres Cycles editors Letters Global Biogeochemical Cycles

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2020 Cited Referees Not Pictured

Juan Pablo Canales Bert Rudels JGR-Solid Earth editors JGR-Oceans editors JGR-Solid Earth JGR-Oceans

Johanna Engström Christian Schoof Earth’s Future editors Mathieu Morlighem Jin-Yi Yu Chao Yue Earth’s Future Geophysical Research Letters Christina Patricola JGR-Space Physics editors Geophysical Research JGR-Space Physics Lujia Feng Quanqi Shi Letters JGR-Solid Earth editors JGR-Space Physics editors JGR-Solid Earth JGR-Space Physics

Juan Pascual García Mathieu Vincendon Sana Salous JGR-Planets editors Radio Science JGR-Planets

Idiko Horvath Jingfeng Wang JGR-Space Physics editors Earth and Space Science editors JGR-Space Physics Earth and Space Science

Cin-Ty Lee Qingju Wu Global Biogeochemical Cycles editors JGR-Solid Earth editors Edward D. Zaron Hongbin Zhan Global Biogeochemical Cycles JGR-Solid Earth JGR-Oceans editors Water Resources Research JGR-Oceans editors Janet Luhmann Nana Yoshimitsu Water Resources Research Andrew Yau JGR-Solid Earth editors Geophysical Research Letters JGR-Solid Earth

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50 Eos // AUGUST 2021 RESEARCH SPOTLIGHT

South Pole Ice Core Reveals History of Antarctic Sea Ice

racking seasonal changes in sea ice over millennia can give sci- away each year, the core’s chemical profiles can indicate how much sea entists a better understanding of just how much variation is ice existed from season to season across an entire epoch. Tnatural, as well as how these yearly variations interact with long-­ ​ The researchers discovered an increase in wintertime sea ice between ­term climate patterns. Although annual fields of reflective ice are 8,000 and 10,000 years ago, followed by an abrupt decrease 5,000–6,000 carefully monitored today, it is difficult to accurately discern the extent years ago. The sudden decrease, concentrated in the South Atlantic of summer or winter sea ice from times before satellite imagery. There- region, accompanied an increase in sea ice in the Northern Hemisphere. fore, the question remains, How can scientists follow these data back According to the authors, this moment likely marks a change in sea tens of thousands of years? currents affecting local and global climate. In a new study, Winski et al. track sea salt levels from the South Pole Changes in sea ice can lead to rapid climate change, which affects the Ice Core project to follow sea ice patterns over more than 11,000 years. entire planet. This study fills in the details on this ephemeral but vital According to a chemical transport model, storms carry sea salt from sea indicator, the authors say. (Geophysical Research Letters, https://­doi.org/​ ­ ice inland to the core’s location. Although most of the sea ice itself melts 10​.1029/­2020GL091602, 2021) —Elizabeth Thompson, Science Writer

Carbonate Standards Ensure Better Paleothermometers

the tiny amounts of heavy isotopes in that gas with the abundances expected by random chance, based on a set of carbon dioxide gases. This standardization, known as the absolute reference frame or carbon dioxide equilibra- tion scale, corrects for differences between individual mass spectrometers and partially enables interlaboratory comparisons. The cor- rection, however, doesn’t account for differ- ences in sample preparation. The authors of this new study propose stan- dardization using carbonate reference mate- rials, which require processing with acid, just like the samples being investigated, instead of with gases. To validate the approach, 22 labo- ratories analyzed three reference carbonates and four unknown carbonate samples. When measurements of the unknown samples were corrected using average values for the refer- Anna-Nele Meckler, a researcher at the University of Bergen, Norway, works with a loading instrument for ences, discrepancies between laboratories clumped isotope analysis. Credit: Eivind Senneset reflected expected uncertainty rather than dramatic differences due to sample prepara- tion as reported in previous studies. The approach proposed by the authors— he climate of ancient Earth left telltale ­clumped-​­isotope thermometry, using com- the ­InterCarb-​­Carbon Dioxide Equilibrium signs in the geochemical record. On the mon carbonate standards. Scale (I-­ CDES)—will​­ support standardization Tbasis of chemical properties of carbon- Carbonate ­clumped-isotope​­ thermometry between laboratories and facilitate future ate minerals, scientists can calculate what a relies on a thermodynamic tendency for rare investigation by the ­clumped-​­isotope com- site’s temperature was hundreds of millions heavy isotopes of oxygen and carbon to bond, munity to understand Earth’s past. (Geo- of years ago. Such a “paleothermometer” or clump together, in carbonate molecules. At chemistry, Geophysics, Geosystems, https://­doi​ provides a peek not just into past climates but lower temperatures, the molecules are more .org/­10.1029/​ ­2020GC009588, 2021) —Jack Lee, also into geological processes like elevation likely to form with clumped isotopes; scien- Science Writer changes to Earth’s surface. Analyses by dif- tists can use this fact to calculate tempera- ferent research groups, however, don’t tures on ancient Earth. always agree. For analyses, researchers treat carbonate A new study by Bernasconi et al. describes a samples, from seafloor mud to megalodon u Read the latest news community effort, InterCarb, to standardize teeth, with acid to produce carbon dioxide gas. at Eos.org the chemical analysis known as carbonate They then use mass spectrometers to compare

SCIENCE NEWS BY AGU // Eos.org 51 RESEARCH SPOTLIGHT

‘Oumuamua May Be an Icy Fragment of a Pluto-­ ​­Like Exoplanet

n October 2017, for the first time in history, astronomers spotted an acteristics, the researchers narrowed down a list of potential materials. interstellar object on its journey through our solar system. The inter- They found that the substance that best fits all of the clues is nitrogen Iloper? ‘Oumuamua, a shiny object with a flattened body about half a ice. city block long. Nitrogen is not an exotic material in our own solar system, the Since then, scientists have followed many clues in attempts to deter- authors note. For instance, Pluto and Triton, the largest moon of Nep- mine what ‘Oumuamua is made of—and where it might have begun its tune, are swathed in nitrogen ice. Therefore, ‘Oumuamua could have journey. Some have hypothesized that it is made of hydrogen ice or originated from a Pluto-­ like​­ exoplanet that ejected numerous icy frag- water ice. ments from its surface. Now Jackson and Desch present a new analysis that suggests the mys- Further calculations suggest that ‘Oumuamua may have been terious object is made primarily of nitrogen ice and may have been launched into space about half a billion years ago in a solar system ejected from the surface of a ­Pluto-​­like body orbiting a star in another potentially located in the Perseus arm of the Milky Way. Ejection from solar system. the exoplanet could have resulted from orbital instabilities similar to The new analysis takes into account ‘Oumuamua’s size, its shininess, those seen early in our own solar system’s history. ( Journal of Geophys- the conditions it has been exposed to in interstellar space, and the com- ical Research: Planets, https://doi­ ​.org/10­ ​.1029/2020JE006706,­ 2021) ponent of its acceleration that is not due to gravity. Using these char- —Sarah Stanley, Science Writer

A 50,­000-​­Year History of Current Flow ​ Yields New Climate Clues

rom 50,000 to 15,000 years ago, during the last ice age, Earth’s climate wobbled Fbetween cooler and warmer periods punctuated by occasional, dramatic ­ice-​ ­melting events. Previous research has suggested that these oscillations were likely influenced by changes in the Atlantic Meridional Overturning Circu- lation (AMOC), a pattern of currents that carry warm, tropical water to the North Atlantic, where it cools, sinks, and flows back south. However, the precise role played by the AMOC in ancient climate fluctuations has been unclear. Now Toucanne et al. have reconstructed the historical flow of a key current in the upper An iceberg floats off of Baffin Island, Nunavut, Canada, in the North Atlantic Ocean, a region that plays a key part (the northward flow) of the AMOC, the role in ocean circulation. Credit: National Snow and Ice Data Center, CC BY 2.0 (bit.ly/ccy 2-0) Glacial Eastern Boundary Current (GEBC), shedding new light on how the AMOC can drive sudden changes in climate. The GEBC flowed northward along Europe’s This new historical record shows that the Atlantic, correspond with periodic weakening continental margin during the last ice age (it GEBC flowed faster during warmer intervals of the current and of the AMOC in general. persists today as the European Slope Cur- of the last ice age but weakened during the Drawing on these findings, the researchers rent). To better understand the GEBC’s role coldest periods. The timing of these changes outline a mechanism by which the GEBC in the AMOC, the researchers collected six aligns well with previously established could have carried cold glacial meltwater seafloor sediment cores off the coast of records on AMOC speed and the southward northward and contributed to changes in the France. Analysis of grain sizes and isotope return flow of deep waters to the west. AMOC that may have driven ­warm-​­cold cli- levels in the core layers revealed the current’s Comparing the history of the GEBC with mate oscillations in the North Atlantic. (Pale- strength when each layer was deposited, other records also shows that major ice-­ ​ oceanography and Paleoclimatology, https://­doi​ yielding the first ­high-​­resolution, 50,­000-​ ­melting events, in which ice age glaciers .org/­10​.1029/­2020PA004068, 2021) —Sarah ­year historical record of the current. released huge amounts of fresh water into the Stanley, Science Writer

52 Eos // AUGUST 2021 AGU ADVANCES EDITORS PRESENT THE LATEST RESEARCH // EDITORS’ HIGHLIGHTS

Dune Aurora Explained by Combined ​ Satellite–Ground­ Observations

randin et al. present new observations of auroral dunes, a phe- nomenon that has been photographed over northern Europe by Gamateur astronomers. Their features are similar to those of typical aurorae in terms of their light emission characteristics, but their structure is more banded. The authors suggest that the underlying mechanism for this banded structure is modulation of the atmospheric density by a horizontally propagating atmospheric bore, following a waveguide formed by a temperature inversion detected in the upper mesosphere. Auroral particle excitation of the bore’s trailing wave pattern results in the appearance of the dunes. Combining surface and satellite observations, the authors derive a wavelength and propagation speed for the dune feature, relating the latter to characteristics of the upper mesosphere. Strong horizontal neutral winds and electron pre- Auroral dunes are seen in the sky in this photo taken from Aura, Finland, on cipitation play roles. (https://doi­ ​.org/10­ ​.1029/2020AV000338, 2021) 20 January 2016. Credit: Grandin et al., 2021 —Mary Hudson

Urban Vegetation a Key Regulator ​ for Heat Island Intensity

Maps of London show the average (a) surface daytime temperature, (b) vegetation activity, and (c) leaf area index during summer. Solid lines show the boundaries of the city clusters, and dashed lines, the boundaries of the rural surrounding. Credit: Paschalis et al., 2021

igh temperatures in urban areas expose many people to poten- areas in cities leads to a strong decrease in leaf area index and weaker tially dangerous heat stress. Paschalis et al. used state-­ of-​­ the-​­ art​­ evaporative cooling. Hsatellite data for 145 city clusters to disentangle the drivers of These results highlight the importance of preserving urban forests as surface urban heat island intensity (SUHI) and to quantify ­urban–​­rural natural reserves for reducing the daytime surface urban heat island effect, differences in vegetation cover, species composition, and evaporative rather than simply for “greening” cities. (https://doi­ ​.org/­10.1029/­ cooling. 2020AV000303, 2021) —Donald Wuebbles They found that daytime SUHIs are highly correlated with vegetation characteristics and the wetness of the background climate. The mag- nitude and seasonality of daytime SUHIs are controlled by ­urban–​­rural differences in plant transpiration and leaf area, explaining the depen- u Sign up for the AGU Advances digest: dence of SUHIs on wetness conditions. Urban vegetation is the most agu.org/advances-digest important factor in regulating SUHIs. A reduced fraction of forested

SCIENCE NEWS BY AGU // Eos.org 53 The Career Center (findajob.agu.org) is AGU’s main resource for recruitment advertising. PLACE AGU offers online and printed recruitment advertising in Eos to reinforce your online job visibility and your brand. Visit YOUR employers.agu.org for more information. AD HERE Packages are available Visit agu.org/advertise to learn more for positions that are about employment advertising with AGU.

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54 Eos // AUGUST 2021 POSITIONS AVAILABLE

Assistant Professor (Tenure Track) of Engineering Geology

→ The Department of Earth Sciences (www.erdw.ethz.ch) at ETH Zurich invites applications for the above-mentioned position.

→ The professorship offers long-term funding to create and oversee an innovative research programme directed at engineering geology. Specific relevant disciplines include the geological aspects of engineered structures (tunnels, bridges, dams, landfills, nuclear repositories), development of near-surface resources (groundwater, geothermal energy, carbon sequestration and mineral deposits) and the assessment and mitigation of geohazards and geo- risks. The successful candidate will combine an array of approaches, e.g., field measurements, in-situ laboratories, remote sensing technology and numerical simulations at scales ranging from the laboratory to the large field scale. A strong analytical background is expected. She or he has a proven record of innovative research, and the ability to connect with companies and government agencies dealing with Engineering Geology topics of high societal rele- vance.

→ At the assistant professor level, commitment to teaching and the ability to lead a research group are expected. The new professorship will contribute to introductory and advanced courses in engineering geology, and teach relevant field and laboratory methods, albeit at the moderate level recommended by ETH for assistant professors.

→ Assistant professorships have been established to promote the careers of younger scientists. ETH Zurich imple- ments a tenure track system equivalent to other top international universities. In exceptional circumstances we will also consider an appointment at the level of Full Professor.

→ The Department of Earth Sciences at ETH Zurich is actively striving to increase the number of women professors in order to build a more diverse scientific community.

→ Please apply online: www.facultyaffairs.ethz.ch

→ Applications should include a curriculum vitae, a list of publications, a statement of future research and teaching interests, and a description of the three most important achievements. The letter of application should be addressed to the President of ETH Zurich, Prof. Dr. Joël Mesot. The closing date for applications is 15 September 2021. ETH Zurich is an equal opportunity and family friendly employer, strives to increase the number of women professors, and is responsive to the needs of dual career couples.

SCIENCE NEWS BY AGU // Eos.org 55 CROSSWORD

Distant Wanderers By Russ Colson, Minnesota State University Moorhead

ACROSS 1 2 3 4 5 6 7 8 9 10 11 12 13 1 A core group 6 Relating to a hose-like feature—and 14 15 16 rhyming with ruble 11 What the gravity of one exoplanet might do to another, revealing its presence 17 18 19 14 Said not just in your head 15 Clear, as a file 20 21 22 16 Cellular messenger (abbr.) 17 Hydrogen- and helium-rich exoplanet more than 10 times more massive than 23 24 25 26 27 28 our own world with a rocky or metal core 19 It transports energy (abbr.) 20 Type of type—or a chalk-eating urge 29 30 31 32 21 Start for “-logical” 23 A good thing to do with a job tip 33 34 35 36 37 27 Monkey type 29 Dendritic growth common in forests 30 Apple seed 38 32 Oil platforms 33 Word in ppm 39 40 41 42 43 44 45 34 Exoplanets up to twice the size of our own world 38 Ellipticals and ___ (galaxies) 46 47 48 39 Rocky (silicate) exoplanets similar in size to our own world or smaller 49 50 51 52 53 54 43 Baseball or hub, e.g. 46 Medication 47 Affirmative 55 56 57 48 Snowball world of The Empire Strikes Back 49 Native tribe of the Mississippi Valley whose first five letters spell a type of garment 58 59 60 61 62 63 52 A planet with an axis of rotation not perpendicular to its plane of ecliptic? Or 64 65 66 well-spiced 55 Planets that have not cleared their orbit, like Pluto 67 68 69 57 One measure of the size of an exoplanet that, with 58 across, hints at planet composition 58 One measure of the size of an exoplanet (abbr.) that, with 57 across, hints at planet 5 Education Company (abbr.) 36 Seen in the middle of Ireland composition 6 Place to start a drive 37 Language for the eyes (abbr.) 59 Gas giant–type exoplanets orbiting near 7 Internet address (abbr.) 39 Abbr. for a planetary dynamical their stars 8 Something on a hook timescale 64 Piggy’s play pen? 9 One who questions 40 Scholarly 65 Planet that has left its star 10 Something specific on a hook 41 Landing strips 66 They might emerge when many lamps 11 Method used to discover exoplanets 42 Ending for “geo-” that yields the name are rubbed? in which variations in light intensity of a U.S. state 67 “The” in Avignon with time are measured 43 Government’s just power derives from 68 Stone obelisk 12 Soft, as in “camping with temperature this—U.S. Declaration of Independence 69 Higher than tenors control is so ___” 44 What the fox did to the Gingerbread Man 13 Fulton ___: a range of sizes in which 45 Terminal degree (abbr.) DOWN few exoplanets exist, yielding clues 48 Low-cost lodging facility 1 Preserve, as garden produce to planetary formation 50 Units of academic time load (abbr.) 2 Ginger ___ 18 Nope 51 “The game is ___” 3 Method used to discover exoplanets in 22 Monsieur in Mainz 53 Increase (with “up”) which shifts in wavelengths of light with 23 Protocol for moving files (abbr.) 54 Endangered antelope time are measured 24 Raw resource 56 “All the wrld’s a ___, and all the men 4 Titanium ore mineral 25 On a high horse and women merely plyrs” 26 South Dakota capital and a former 58 Internet access option Canadian prime minister 60 Apr, May, Jun, ___ 28 What the punctured tire says? 61 Fictional United Earth Alliance (abbr.) 31 Envy is a kind of ___ —John Gay 62 Word in John Wayne movie titles (with See p. 50 for the answer key. 34 157.5 deg. Grande, Lobo, or Bravo) 35 Ending for sit, set, cut, and mash 63 A type of sib

56 Eos // AUGUST 2021