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Clarification: 20 June 2019. See full text. NEWS FEATURES THE CALM BEFORE THE STORMS Downloaded from http://science.sciencemag.org/ A spotless sun, as seen in May by NASA’s Solar Dynamics Observatory. The sun is nearing on September 13, 2019 solar minimum. Scientists studying the 11-year solar cycle are trying to predict when a quiet sun will next turn violent or all of February the sun is nearly By Sarah Scoles, lar maximum can damage their technologies. spotless, a smooth circle filled in in Boulder, Colorado Sunspots can be seen with the naked eye, with a goldenrod crayon. It has been but it wasn’t until the mid-1800s that astrono- more than a decade since it was so will reach its peak, and how unruly it will be- mers realized they come and go on a rough lacking in sunspots—dark magnetic come. As light reflects off snow caught in the schedule. They first appear at midlatitudes knots as big as Earth that are a baro- trees and streams through the tall windows and then proliferate, migrating toward the meter of the sun’s temperament. Be- of a conference room, the Solar Cycle 25 Pre- equator over about 11 years. In 1848, Swiss low the surface, however, a radical diction Panel comes to order. NASA and the astronomer Johann Rudolf Wolf published transition is afoot. In 5 years or so, National Oceanic and Atmospheric Adminis- an account of the sunspot record, identi- the sun will be awash in sunspots and more tration (NOAA) have sponsored these panels fying 1755–66 as “Cycle 1,” the first period Fprone to violent bursts of magnetic activity. since 1989, aiming to understand what drives when counts were reliable. He then created Then, about 11 years from now, the solar cycle the sun’s 11-year cycles and assess methods a formula for counting the number of daily will conclude: Sunspots will fade away and for predicting them. But the exercise is not sunspots—a somewhat subjective technique the sun will again grow quiet. just academic: The military, satellite opera- that has evolved into a counting method used In early March, a dozen scientists descend tors, and electric utilities all want to know today to marry data sets across the centuries. on the National Center for Atmospheric Re- what the sun has in store, because the flares The cycles are capricious, however. search (NCAR) here to predict when the sun and bursts of charged particles that mark so- Sometimes, the sun goes quiet for decades, TEAMS AND HMI SCIENCE EVE, AIA, NASA/SDO; PHOTO: 818 31 MAY 2019 • VOL 364 ISSUE 6443 sciencemag.org SCIENCE Published by AAAS Clarification: 20 June 2019. See full text. NEWS with anemic sunspot counts across several jut out from the surface, forming sunspots. effect of such an event on computers and cycles—as occurred during the 19th century’s The sun’s ebb and flow affects Earth. Its communications would be dire. Financial so-called Dalton minimum. Such variations upper atmosphere absorbs the sun’s ultra- transaction systems could collapse. Power are what the scientists at NCAR have gath- violet rays, which dim slightly at solar mini- and water could easily go out. “It probably ered to forecast. The problem is that no one— mum. That causes the atmosphere to cool would be The Hunger Games pretty soon,” in this room or elsewhere—really knows how and shrink, reducing friction for low-flying McIntosh says. the sun works. satellites. In calm solar cycles, operators as- McIntosh doesn’t question the need to Most models snatch at reality, but none sume their satellites will remain in orbit for prepare, but he is skeptical of the panel’s ap- pieces together the whole puzzle. The last longer—and because the same goes for space proach. In fact, he believes its very premise— time the panel convened, in 2007, its scien- junk, the risk of a collision goes up. The predicting the rise and fall of sunspots—is tists evaluated dozens of models and came up sun’s magnetic field also weakens at solar off-base. Sunspots, and the cycle itself, are with a prediction that was far from perfect. minimum, which poses another threat to sat- just symptoms of a still-mysterious story It missed the timing of the maximum, April ellites. The weakened field rebuffs fewer ga- playing out inside the sun. 2014, by almost a year, and also the over- lactic cosmic rays, high energy particles that Lika Guhathakurta, a panel observer from all weakness of the past cycle. This panel, can flip bits in satellite electronics. NASA’s Ames Research Center in California, a who’s who list of solar scientists, doesn’t agrees. “Sunspot is not a physical index of know whether it will do better. anything,” she says, after the morning’s in- As the NCAR clock ticks toward the start “If you design a satellite for troductory talks. “So the fact that we have time, the panelists sit in awkward silence, used it as a proxy in itself kind of presents a clutching their compostable coffee cups. problem.” Using sunspots—a side effect, not a 10- or 12-year life, Downloaded from They know what the next 4 days hold: fights a cause—to predict the sun’s future behav- over physics and intuition, belief and data, you need to consider the cycle.” ior is like trying to divine the germ theory of correlation and causation. Tensions shadow disease by looking at a runny nose, she and Michael Martinez, Maxar the gathering: Scott McIntosh, director of McIntosh think. NCAR’s High Altitude Observatory (HAO) But because the panelists have convened here, has an office above the meeting room At solar maximum, in contrast, the sun specifically to predict sunspot numbers, they and his own unorthodox view of what drives heats and inflates Earth’s upper atmo- soldier on, reviewing about 60 models over http://science.sciencemag.org/ the solar cycle and how to predict it. But Mc- sphere, and it often flares up and unleashes the next 4 days. Each predicts the number Intosh, outspoken and provocative, has not its own particles. They are not as energetic of sunspots at solar maximum, as well as the been invited to be on the panel, although a as the galactic cosmic rays, but they come in timing of minimum and maximum. collaborator will present the HAO’s research. a flash flood. At solar max, Biesecker says, Many of the models rely on “precursors”— At 8:30 a.m., the panel’s earnest leader, these “coronal mass ejections” of charged observable proxies, not unlike sunspots Doug Biesecker—who works at NOAA’s Space particles are 10 times as frequent as at themselves, that have proved to be empiri- Weather Prediction Center here and com- minimum. Hours or days after the sun spits cally useful in predicting the timing or mag- mutes by bike regardless of the weather— them out, particles rush into Earth’s mag- nitude of solar maximum. A popular one is welcomes everyone to the task: sorting netic field, provoking geomagnetic storms the magnetic field strength at the sun’s poles through the many models and coming to a that can last for days. The storms can dis- at solar minimum. Telescopes can measure on September 13, 2019 consensus about the next cycle. “The mess rupt communications, interrupt spacecraft this field strength by gauging how atoms that you get from the community needs to and missile tracking, and skew GPS mea- above the sun’s surface absorb certain wave- be synthesized into something that is ideally surements. They can also induce powerful lengths of light. A weak field usually heralds a correct,” Biesecker says. “But you know, how currents in electric grids, which can destroy quiet cycle, because the polar fields represent can we know what’s going to be correct?” transformers and other equipment. Air the seeds that will punch through as sunspots They can’t. crews at high altitudes, particularly near and grow into the activity of the coming solar As if to prove the point, 14 surprise sun- the poles, can be showered with the sun’s cycle. Robert Cameron, a panelist and solar spots appear, seething on the surface that energetic particles—a cancer risk. physicist at the Max Planck Institute for Solar had been so featureless for so long. All of which adds to the practical impor- System Research in Göttingen, Germany, says tance of the panel’s forecasts. “If you de- that over about four cycles of direct observa- EVEN ON ITS CALMEST DAYS, the sun is roiling. sign a satellite for a 10- or 12-year life, you tion and more than a century of indirect data, Fueled by fusion in its core, the sun is a ball of need to consider the cycle,” says Michael the correlation “is good and highly statisti- hot, charged particles, or plasma, that churns Martinez, vice president of mission opera- cally significant.” constantly, generating electric currents that tions at Maxar in Westminster, Colorado, Other precursor models rely on effects of in turn induce magnetic fields. Deep inside which makes high-resolution imaging orbit- the solar cycle on Earth. For 170 years, for ex- the sun is a dense radiative zone, where pho- ers. Designers need to be sure a satellite has ample, observatories around the world have tons slowly fight their way outward. At a cer- enough propellant to combat the friction tracked disturbances in Earth’s magnetic tain point—in the outer third of the sun—the of an expanding atmosphere as the sun ap- field, which tend to be more frequent at solar plasma cools enough to allow convection, a proaches maximum, and they need to shield maximum.