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THE FREE MULTIMEDIA MAGAZINE THAT KEEPS YOU UPDATED ON WHAT IS HAPPENING IN SPACE

Bi-monthly magazine of scientific and technical information ✶ November-December 2020 Small molecules, big questions–the detection of Venusian phosphine

• A planet-forming disc torn apart by its three central stars • Hubble maps a giant halo around the Andromeda galaxy • A spectacular supernova time-lapse • Hubble captures crisp new image of Jupiter and Europa

The Anthropocene as an interstellar messenger

Good morning Earth. This is ET radio!

www.astropublishing.com ✶✶www.facebook.com/astropublishing [email protected] colophon EN_l'astrofilo 29/10/2020 11:43 Page 2

ESO Calendar 2021 Now Available https://www.eso.org/public/usa/shop/product/calendar_2021/

The 2021 edition of one of our most popular products, the ESO Calendar, is now available and can be purchased from the online ESOshop and in the ESO Supernova Planetarium & Visitor Centre.

The calendar’s cover features a spectacular starscape around the relatively unknown central object, Gum 15, a nebula in which stars are being born. The image also features one of the closest supernova remnants to Earth, which exploded between 11,000 and 12,300 years ago and is located 800 light-years away from our cosmic home.

For the month of March, the bright band of the Milky Way arcs above the ALMA antennas on the Chajnantor plateau. One of the closest stellar nurseries to Earth, the Orion Nebula, is the chosen image for July and the massive 3-tonne blank for the Extremely Large Telescope’s (ELT) secondary mirror is the star of September. Finally, in December the viewer will feel they are speeding towards the centre of our galaxy, thanks to a clever photographic technique used on an observation of the Milky Way. These are just a few highlights, we invite you to view the individual pages of the ESO Calendar 2021 here.

The calendar has a total of 14 pages, and is available for 9.50 EUR in the ESOshop — but stock is limited so don’t delay! colophon EN_l'astrofilo 29/10/2020 11:43 Page 3

S U M M A R Y

BI-MONTHLY MAGAZINE OF SCIENTIFIC AND TECHNICAL INFORMATION Small molecules, big questions – the detection of Venusian phosphine FREELY AVAILABLE THROUGH On the local morning of September 14th, the Royal Astronomical Society tweeted an announcement for THE INTERNET an afternoon press briefing about a significant discovery. Within hours, “phosphine” and “Venus” were being proposed by some on social media as the discussion topic. In combination with shared links to the... November-December 2020 4

A planet-forming disc torn apart by its three central stars A team of astronomers have identified the first direct evidence that groups of stars can tear apart their planet-forming disc, leaving it warped and with tilted rings. This new research suggests exotic planets, 16 not unlike Tatooine in Star Wars, may form in inclined rings in bent discs around multiple stars. The...

Hubble maps a giant halo around the Andromeda galaxy In a landmark study, scientists using NASA’s Hubble Space Telescope have mapped the immense enve- lope of gas, called a halo, surrounding the Andromeda galaxy, our nearest large galactic neighbor. Scien- 20 tists were surprised to find that this tenuous, nearly invisible halo of diffuse plasma extends 1.3 million...

The Anthropocene as an interstellar messenger It seems incredible, but in an age when humans communicated remotely using horseback couriers, car- rier pigeons, fires and mirrors, the first signals were already being transmitted into space. The Roman, 24 Chinese and Spanish empires unwittingly added traces of their existence to the light reflected from the... English edition of the magazine lA’ STROFILO Hubble captures crisp new image of Jupiter and Europa This latest image of Jupiter, taken by the NASA/ESA Hubble Space Telescope on 25 August 2020, was cap- Editor in chief tured when the planet was 653 million kilometres from Earth. Hubble’s sharp view is giving researchers Michele Ferrara 34 an updated weather report on the monster planet’s turbulent atmosphere, including a remarkable new... Scientific advisor Prof. Enrico Maria Corsini Good morning Earth. This is ET radio! Publisher Astro Publishing di Pirlo L. The patchy search for alien civilizations in the Milky Way continues tirelessly. Nearly all surveys are fo- Via Bonomelli, 106 cused on radio waves, and will continue to be in the future, thanks largely to the planning of gigantic 25049 Iseo - BS - ITALY networks of radio telescopes, such as the Square Kilometer Array, soon to be built in Australia and... email [email protected] 38 Internet Service Provider Aruba S.p.A. A spectacular supernova time-lapse Via San Clemente, 53 24036 Ponte San Pietro - BG - ITALY The NASA/ESA’s Hubble Space Telescope has tracked the fading light of a supernova in the spiral galaxy NGC 2525, located 70 million light-years away. Supernovae like this one can be used as cosmic tape mea- Copyright sures, allowing astronomers to calculate the distance to their galaxies. Hubble captured these images... All material in this magazine is, unless 48 otherwise stated, property of Astro Publishing di Pirlo L. or included with permission of its author. Reproduction or retransmission of the materials, in whole or in part, in any manner, with- out the prior written consent of the copyright holder, is a violation of copy- right law. A single copy of the materi- als available through this course may be made, solely for personal, noncom- mercial use. Users may not distribute such copies to others, whether or not in electronic form, whether or not for a charge or other consideration, with- out prior written consent of the copy- right holder of the materials. The publisher makes available itself with having rights for possible not charac- terized iconographic sources.

Advertising - Administration Astro Publishing di Pirlo L. Via Bonomelli, 106 25049 Iseo - BS - ITALY email [email protected] phosphine EN_l'Astrofilo 28/10/2020 17:57 Page 4

4 ASTROCHEMISTRY

Small molecules,bi detection of Venus

by Damian G. Allis NASA Solar System Ambassador

On the local morning of September 14 th, the Royal Astronomical Society tweeted an announcement for an afternoon press briefing about a significant discovery. Within hours, “phosphine” and “Venus” were being proposed by some on social media as the discussion topic. In combination with shared links to the January 2020 Astrobiology article “Phosphine as a Biosignature Gas in Exoplanet Atmospheres,” some were already anticipating a most remarkable event.

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ASTROCHEMISTRY 5 big questions–the usian phosphine

n artist’s vi- n international team from the UK, ing and multi-disciplinary discovery to A sion of elec- USA, and Japan, led by Prof. Jane fruition was obvious to all in attendance. trical discharges A Greaves of Cardiff University, re- No topic in science generates more specu- in the hot sky of leased their open access article “Phosphine lation than extraterrestrial life, and the Venus. Lightning gas in the cloud decks of Venus” in Nature discoverers will go down in history for and volcanism Astronomy as the press briefing was tak- that achievement − this would clearly be a could be the ori- gin of the re- ing place. The cautious excitement of milestone as the names “Gagarin” and cently discovered Greaves, Dr. Anita Richards (Jodrell Bank “Armstrong/Aldrin/Collins” conjure. One phosphine in the Centre for Astrophysics), and Dr. William assumes the most benevolent intentions planet’s atmos- Bains and Prof. Sara Seager (MIT) over of such a briefing, especially with the pre- phere. [J. Peter] bringing such a potentially groundbreak- senters stating that their work is of a mo-

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lecular detection and an interpretation in duced by lightning and volcanism, both eft, a false- the absence of any known non-biological common on Venus. That said, the atmos- Lcolor enhance- explanations. That said, one can only imag- pheric and geochemical routes to phos- ment of an origi- ine the instinct to be the first to make such phine could only account for a fraction of nal photograph a discovery, however preliminary, known to the amount detected based on our current of the opaque Venus cloud the world as soon as possible. understanding of both phenomena. The cover taken by What has followed is a story of measure- possible explanation put forth by the au- Mariner 10 during ment, interpretation, reserved speculation, thors applies the predominant method of its gravity-assist and controversy − not over the discovery of phosphine production on Earth – biochem- maneuver en phosphine, but over its indication as a pos- ical processes in low-oxygen conditions. route to Mercury sible biological marker, which has driven As is obvious from the many design fea- in February, 1974. discussion beyond just the astronomical tures of the few successful Venera and Pio- [NASA/JPL] community. What is most Right, the surface clear is how little we still of Venus as cap- know about our own tured by the solar system, as a simple Magellan space- molecule can lead to craft. [Magellan Project/NASA/JPL] heated debate because On the side, an of our incomplete under- artistic enlarge- standing of the chemistry ment of a tiny and geology of our near- region of the est planetary neighbors. Venusian atmos- What we know and do phere, showing not yet know about the the geometry of production of phosphine, the phosphine molecule. [ESO] PH3 , on Venus are central to the past few weeks of speculation. On Earth, phosphine can be pro-

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enusian land- neer missions to land probes V scapes pho- during the 1970’s and early tographed by the 1980’s, the conditions on Venus landers of the can be brutal, with a mean sur- Venera 13 and 14 face temperature of 460 °C. As missions in March one moves higher in altitude, 1982. [Roscosmos] the temperature and pressure decrease to where some at- mospheric zones might feel quite pleasant. That said, only the heartiest microbe or prop- erly suited human would find the zone safe even for short periods. The Venusian atmos- phere is reactive to many small molecules of biological interest − including phosphine. The 96.5% carbon dioxide content drives the “runaway green- house effect” that causes the

extreme surface temperatures. Sulfuric acid clouds obscure the Venusian surface, mak- ing radar the source of our mapping from orbit of the near-entirely of the planet. Beyond the 3.5% additional nitrogen con- tribution, all other gases are measured in parts-per-million (ppm) or billion (ppb). The 20 ppb-level phosphine detection was accomplished with the James Clerk Max- well Telescope, located high above water vapor at the Mauna Kea Observatory in Hawaii, and was confirmed using the Ata- cama Large Millimeter/submillimeter Array (ALMA), itself located high in the arid Ata- cama Desert in northern Chile. During the press briefing, you could sense the scientists trying to reign in the rampant speculation of viewers to focus on how the detection of phosphine is of consequence because we do not have an explanation for how such concentrations could exist in the Venusian atmosphere given what we know

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on Earth about its production. Such an inter- This detection adds a piece of hard data to bove, the At- pretation is another example of the princi- a debate that, for much of our history, has Aacama Large ple of mediocrity, a topic of the July-August been driven merely by our knowledge of Millimeter/sub- 2020 issue. If phosphine is produced on Earth other planets. The ability to apply hard sci- millimeter Array, by life and we’ve no other mechanism for its ence to the exobiology question was high in northern Chile. [W. Gar- production in significant quantities, we can founded largely on scientific developments nier, ALMA/ESO/ − at our potential peril and misunderstand- at the end of WWII and the political race NAOJ/NRAO] ing − attribute its presence elsewhere to sim- to prove the superiority of political ideolo- Below, the James ilar biological processes. gies during the Cold War – radar tech- Clerk Maxwell nology, detectors Telescope, Mauna across the electro- Kea Observatory, magnetic spec- Hawaii. [William trum, satellites, Montgomerie] and interplanetary propulsion. This is why the appear- ance of more data- driven speculation in the scientific lit- erature, as well as more focus about life far less techno- logically advanced than our own, only began start- ing in the 1960’s. A relevant paper was published in Science by Carl

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his video Sagan in 1961, titled T summarizes “The Planet Venus.” In the discovery of it, he comments on phosphine in the the likelihood of de- atmosphere of tecting life on the sur- Venus. [ESO] face: “...it appears Below, the unfor- gettable Carl quite certain that ter- Sagan (with the restrial organisms de- famous message posited on the surface sent on Pioneer of the planet would probes), who, quickly be killed. Con- sixty years ago, sequently, there seems had already hy- little danger of biolog- pothesized the ical contamination of possible existence the surface of Venus.” of life in the up- Enough was then per atmosphere known about the Venusian atmosphere sion in 1982. The consensus now is that the of Venus. [CBS that its possible hosting of simple lifeforms disc-like and scorpion-like creatures were, via Getty images] could not so easily be ruled out. Sagan in fact, lens caps and processing artifacts – wrote: “conditions are much more favor- a clear example of the inverse relationship able at higher altitudes, especially just be- between data and speculation. neath the cloud layer, and there is the Anyone basing Venusian life on the single- distinct possibility of biological contamina- celled organisms inhabiting ponds on Earth tion of the upper Cytherean atmosphere.” would have to take dramatic leaps in biol- The most recent data-driven analysis of Ve- ogy to make such organisms robust enough nusian life harkens back to the days of Per- to survive the hyper-acidic, poisonous, and cival Lowell and his Martian canals, with water-poor conditions of the upper Venu- the Russian scientist Leonid Ksanfomaliti sian atmosphere. That said, similar leaps claiming to have found life in images sent already abound on Earth. A few examples back from the Soviet Venera 13 lander mis- include thermococcus gammatolerans, which can survive high doses of gamma radiation, pyrococcus furiosus, which thrives at the boiling point of water (we sim- ple surface-dwellers rely on boiling water to kill harmful bacteria), or clostridium para- doxum, which is found in acidic mine drainage and volcanic springs. Extreme conditions call for extreme adaptation. We find organisms on Earth exist- ing in places, including the upper atmosphere, where we would not even think to look for them if not for the constant reminder that life, within a very wide range of environ- ments, always finds a way. Even without an actual life- form, the presence of certain small molecules in planetary

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atmospheres and their attribution to bio- While the detection of methane around a his illustration logical processes is also nothing new, even rocky exoplanet would be a significant dis- T depicts the in our own solar system. Seasonal methane covery, there is another molecule that Venusian surface variations in the Martian atmosphere are would make all of exobiology take notice. and atmosphere, as well as phos- one example. Methane, CH4, is broken down Oxygen presently makes up 21% of Earth’s phine molecules. by UV radiation. The thin Martian atmos- atmosphere, but this percentage would These molecules phere provides little protection from solar itself eventually reduce to zero if not con- float in the wind- radiation, resulting in what should mean stantly replenished through photosynthe- blown clouds at the eventual depletion of methane. That it sis. In fact, the evolution of life did not altitudes of 55 to is found at all – and changes seasonally – begin with aerobic, or oxygen-consuming, 80 km, absorbing indicates that either some geochemical respiration. It was the evolution of single- some of the mil- limeter waves process is producing methane cyclically or celled organisms capable of photosynthe- that are produced that, possibly, some biological process is oc- sizing CO2 and producing O2 as a waste at lower altitudes. curring that is seasonally restoring atmos- product that ultimately changed the at- [ESO/M. Korn- pheric methane. mosphere, and evolutionary history, of Earth. messer/L. Calçada]

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As we search today, the detection of oxy- to the second planet in its own solar system. gen in an exo-atmosphere does not then Technological sophistication aside, evolu- mean a wealth of multicellular organisms tion on two close planets with different his- but may mean that some simple lifeform tories and surface chemistries dramatically producing oxygen as a waste product might expands what exobiologists know to look be responsible for what we detect. for. But the ramifications of one or more Phosphine, from our current understanding, new lifeforms will not be fully known until falls into the same category as meth-ane scientists are able to determine beyond all and oxygen. Without some source to re- doubt that the lifeform is a product of plenish it, it simply should not be detectable Venus alone. You can, after all, buy Mars in the atmosphere of a rocky planet based rocks − proof that the rocky inner planets on what we currently know of its chemistry. have exchanged materials regularly over If Venus samples reveal a lifeform produc- the history of the solar system. ing phosphine (or any molecule!), Earth Consider just one aspect of Earth biology: would go from being alone in the universe if the DNA of a Venusian lifeform, if it has

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such an information repos- itory, were identical to that of the bases and pair- ings (“A-T” and “G-C”) of life on Earth, it would be easier to accept that either the Venus life or the Earth life came first and one ended up establishing a foothold on the other planet − remembering that early Venus, like early Mars, may have been more hospitable to the chemical processes that began the tree of life we see on Earth today, and that Earth might have be- come the unanticipated beneficiary of eons of fundamentally different chemical processes else- where. If Venusian genetic material were similar, but not quite like DNA, did a small number of processes could have converted one form n artist’s vi- resilient extremophiles from Earth/Venus into another after some ancient pansper- Asion of the survive the long, cold trip to Venus/Earth mic event, then the case for an entirely sep- volcanism and and begin to incorporate similar molecular arate evolutionary course becomes the hazy atmosphere fragments, or have we possibly learned accepted theory until future studies can on the rocky Ve- nusian surface. that a stable chemical information reposi- challenge the separate-evolution theory. [ESA/AOES] tory (like DNA) now is even more estab- In the Nature Astronomy paper, the au- On the left, the lished as at the core of biological life? If thors take known non-biological processes “scorpion” ap- Venusian genetics was fundamentally dif- for phosphine production, including from peared in the im- ferent from that on Earth and there was the known chemistry of the atmosphere ages taken by the no possible way that stochastic chemical and surface of Venus, to further argue for Venera 13 lander, about 90 minutes after landing, and noticed by Leonid Ksanfo- maliti. It was ac- tually an image processing arti- fact. [Roscosmos]

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a potential biological origin. The study of covered for the broad audience. It is an non-biological phosphine sources will un- ethical duty for any scientist to communi- doubtedly come to be a new research focus. cate with the media and the public with Despite our great hope of finding extrater- great scientific rigor and to be careful not restrial life, the scientific community is al- to overstate any interpretation which will ways ready to apply Occam’s Razor to any be irretrievably picked up by the press and such claim. Scientific skepticism at extrater- generate great public attention in the case restrial claims might always be treated as of life beyond Earth.” The interpretation of if an alternative explanation is the more the statement among several members of likely one. As Sagan said, “extraordinary the astronomy community has been varied, claims require extraordinary evidence.” but Oxford Professor and BBC The Sky at Of all of the statements made about the Night host Dr. Chris Lintott has summed up phosphine discovery and analysis, perhaps the thoughts of many, describing the state- the most complicated one was published ment as a “grumpy response of a bunch of by the Organising Committee of Commis- senior people not involved in work that sion F3 of the International Astronomical got public attention.” With the IAU execu- Union itself, which seems to admonish the tive presently calling for the F3 statement authors for even pushing the biological ori- retraction, there has officially been a con- gin hypothesis. From the statement: “the troversy over the possible detection of bi- Commission is concerned with the way the ological processes on Venus, a controversy potential detection of phosphine has been over the F3 response to the controversy, and now any future IAU controversies over the F3 controversy over the response to the controversy. Social media astrophiles are free to sit back and watch how the profes- sionals do it. As will be true for ex- oplanets, it is possible that a strong marker of Venusian biology is already visible to us, but we do not yet rec- ognize it as a marker - either food, waste, ox- idant, or whatever life does as part of its exis- tence. The phosphine discovery bridges one possible gap and, if speculative life always happens to A vision of find a similar way in possible Venusian the universe, its detec- life as described tion could be the be- in the classic in- troductory book ginning of our new National Geo- chapter in the biology graphic Picture of the universe. Until Atlas of Our Uni- then, there remain a verse. [Nat.Geo.] great many studies. !

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images by Massimo Vesnaver chronicles EN_l'Astrofilo 28/10/2020 17:53 Page 16

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A planet-forming disc torn apart by its three central stars by ESO

team of astronomers have identified the first direct ev- A idence that groups of stars can tear apart their planet-forming disc, leaving it warped and with tilted rings. This new research sug- gests exotic planets, not unlike Tatooine in Star Wars, may form in inclined rings in bent discs around multiple stars. The results were made possible thanks to observations with the European Southern Observa- tory’s Very Large Telescope (ESO’s VLT) and the Atacama Large Millime- ter/submillimeter Array (ALMA). Our Solar System is remarkably flat, with the planets all orbiting in the same plane. But this is not always the case, especially for planet-form- ing discs around multiple stars, like the object of the new study: GW Ori- onis. This system, located just over 1300 light-years away in the constel- lation of Orion, has three stars and a deformed, broken-apart disc sur- rounding them. “Our images reveal an extreme case where the disc is not flat at all, but is warped and has a misaligned ring that has broken away from the disc,” says Stefan Kraus, a professor of astrophysics at the University of Exeter in the UK who led the re- search published in the journal Sci- ence. The misaligned ring is located in the inner part of the disc, close to the three stars.

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The new research also reveals that which is planned to start operating raises an exciting prospect: there this inner ring contains 30 Earth- later this decade. Since more than could be an unknown population of masses of dust, which could be half the stars in the sky are born exoplanets that orbit their stars on enough to form planets. “Any plan- with one or more companions, this very inclined and distant orbits. ets formed within the misaligned ring will orbit the star on highly LMA, in which ESO is a partner, and the SPHERE instrument on ESO’s Very oblique orbits and we predict that ALarge Telescope have imaged GW Orionis, a triple star system with a pecu- many planets on oblique, wide-sep- liar inner region. The new observations revealed that this object has a warped aration orbits will be discovered in planet-forming disc with a misaligned ring. In particular, the SPHERE image future planet imaging campaigns, (right panel) allowed astronomers to see, for the first time, the shadow that this for instance with the ELT,” says team ring casts on the rest of the disc. This helped them figure out the 3D shape of the ring and the overall disc. The left panel shows an artistic impression of the inner member Alexander Kreplin of the region of the disc, including the ring, which is based on the 3D shape recon- University of Exeter, referring to structed by the team. [ESO/L. Calçada, Exeter/Kraus et al.] ESO’s Extremely Large Telescope, chronicles EN_l'Astrofilo 29/10/2020 11:32 Page 18

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To reach these conclusions, the team The international observed GW Orionis for over 11 team, which in- years. Starting in 2008, they used the cludes researchers AMBER and later the GRAVITY in- from the UK, Bel- struments on ESO’s VLT Interferom- gium, Chile, France eter in Chile, which combines the and the US, then light from different VLT telescopes, combined their ex- to study the gravitational dance of haustive observa- the three stars in the system and tions with com- map their orbits. “We found that puter simulations the three stars do not orbit in the to understand same plane, but their orbits are mis- what had hap- aligned with respect to each other pened to the sys- and with respect to the disc,” says tem. For the first Alison Young of the Universities of time, they were his ‘fly-through’ animation allows the viewer to see Exeter and Leicester and a member able to clearly link T the three stars at the very centre of GW Orionis, as well as its warped disc and the tilted ring that was torned of the team. the observed mis- apart from it. The animation is based on a computer They also observed the system with alignments to the model of the inner region of GW Orionis, provided by the the SPHERE instrument on ESO’s VLT theoretical “disc- team; they were able to reconstruct the 3D orbits of the and with ALMA, in which ESO is a tearing effect”, stars and the 3D shape of the disc from the observational partner, and were able to image the which suggests data. [ESO/Exeter/ Kraus et al., ALMA (ESO/NAOJ/NRAO)] inner ring and confirm its misalign- that the conflict- ment. ESO’s SPHERE also allowed ing gravitational pull of stars in dif- around them to break into distinct them to see, for the first time, the ferent planes can warp and break rings, which is exactly what they see shadow that this ring casts on the their discs. in their observations. The observed rest of the disc. This helped them Their simulations showed that the shape of the inner ring also matches figure out the 3D shape of the ring misalignment in the orbits of the predictions from numerical simula- and the overall disc. three stars could cause the disc tions on how the disc would tear. Interestingly, another team his ALMA image who studied the same system T shows the disc’s using ALMA believe another in- ringed structure, gredient is needed to under- with the innermost stand the system. “We think ring (part of which is visible as an ob- that the presence of a planet long dot at the very between these rings is needed centre of the to explain why the disc tore image) separated apart,” says Jiaqing Bi of the from the rest of the University of Victoria in Canada disc. The SPHERE who led a study of GW Orionis observations al- published in The Astrophysi- lowed astronomers cal Journal Letters in May this to see for the first year. His team identified three time the shadow of dust rings in the ALMA obser- this innermost ring vations, with the outermost on the rest of the ring being the largest ever ob- disc, which made it served in planet-forming discs. possible for them Future observations with ESO’s to reconstruct its ELT and other telescopes may warped shape. [ESO/Exeter/ Kraus help astronomers fully unravel et al., ALMA the nature of GW Orionis and (ESO/NAOJ/NRAO)] reveal young planets forming around its three stars. !

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Hubble maps a giant halo around the Andromeda galaxy

by NASA/ESA

t a distance of 2.5 million Alight-years, the majestic spiral Andromeda galaxy it is so close to us that it appears as a cigar-shaped smudge of light high in the autumn sky. If its gaseous halo could be seen with the naked eye, it would be about three times the width of the Big Dipper − eas- ily the biggest feature on the nighttime sky. [NASA, ESA, J. DePasquale and E. Wheatley (STScI) and Z. Levay]

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n a landmark study, scientists us- nated with this material from stel- ing NASA’s Hubble Space Tele- lar explosions. The Andromeda gal- Iscope have mapped the immense axy, also known as M31, is a majestic envelope of gas, called a halo, sur- spiral of perhaps as many as 1 trillion rounding the Andromeda galaxy, stars and comparable in size to our our nearest large galactic neighbor. Milky Way. At a distance of 2.5 mil- Scientists were surprised to find that lion light-years, it is so close to us this tenuous, nearly invisible halo of that the galaxy appears as a cigar- diffuse plasma extends 1.3 million shaped smudge of light high in the light-years from the galaxy—about autumn sky. If its gaseous halo could halfway to our Milky Way—and as be viewed with the naked eye, it far as 2 million light-years in some would be about three times the directions. This means that Androm- width of the Big Dipper. This would eda’s halo is already bumping into easily be the biggest feature on the the halo of our own galaxy. nighttime sky. They also found that the halo has a Through a program called Project layered structure, with two main AMIGA (Absorption Map of Ionized nested and distinct shells of gas. This Gas in Andromeda), the study exam- is the most comprehensive study of ined the light from 43 quasars—the a halo surrounding a galaxy. very distant, brilliant cores of active “Understanding the huge halos of galaxies powered by black holes— gas surrounding galaxies is im- located far beyond Andromeda. The mensely important,” explained co- quasars are scattered behind the investigator Samantha Berek of Yale halo, allowing scientists to probe University in New Haven, Connecti- multiple regions. Looking through cut. “This reservoir of gas contains the halo at the quasars’ light, the fuel for future star formation within team observed how this light is ab- the galaxy, as well as outflows from sorbed by the Andromeda halo and events such as supernovae. It’s full of how that absorption changes in clues regarding the past and future different regions. The immense An- evolution of the galaxy, and we’re dromeda halo is made of very rari- finally able to study it in great detail fied and ionized gas that doesn’t in our closest galactic neighbor.” emit radiation that is easily de- “We find the inner shell that ex- tectable. Therefore, tracing the ab- tends to about a half million light- sorption of light coming from a years is far more complex and background source is a better way dynamic,” explained study leader to probe this material. Nicolas Lehner of the University of The researchers used the unique ca- Notre Dame in Indiana. “The outer pability of Hubble’s Cosmic Origins shell is smoother and hotter. This Spectrograph (COS) to study the ul- difference is a likely result from the traviolet light from the quasars. Ul- impact of supernova activity in the traviolet light is absorbed by Earth’s galaxy’s disk more directly affecting atmosphere, which makes it impos- the inner halo.” sible to observe with ground-based A signature of this activity is the telescopes. The team used COS to team’s discovery of a large amount detect ionized gas from carbon, sili- of heavy elements in the gaseous con and oxygen. An atom becomes halo of Andromeda. Heavier ele- ionized when radiation strips one or ments are cooked up in the interi- more electrons from it. ors of stars and then ejected into Andromeda’s halo has been probed space — sometimes violently as a before by Lehner’s team. In 2015, star dies. The halo is then contami- they discovered that the halo is large

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and massive. But there about 4 billion years was little hint of its from now. complexity; now, it’s Scientists have studied mapped out in more gaseous halos of more detail, leading to its size distant galaxies, but and mass being far those galaxies are much more accurately deter- smaller on the sky, mined. meaning the number of “Previously, there was bright enough back- very little information— ground quasars to only six quasars—within probe their halo is usu- 1 million light-years of ally only one per galaxy. the galaxy. This new Spatial information is program provides much therefore essentially more information on lost. With its close prox- this inner region of An- imity to Earth, the dromeda’s halo,” ex- gaseous halo of An- plained co-investigator dromeda looms large J. Christopher Howk, on the sky, allowing for also of Notre Dame. a far more extensive “Probing gas within this sampling. radius is important, as his illustration shows the location of the 43 quasars scientists used “This is truly a unique it represents something T to probe Andromeda’s gaseous halo. These quasars are scattered experiment because of a gravitational sphere far behind the halo, allowing scientists to probe multiple regions. only with Andromeda Looking through the immense halo at the quasars’ light, the team of influence for An- do we have informa- observed how this light is absorbed by the halo and how that ab- dromeda.” sorption changes in different regions. By tracing the absorption of tion on its halo along Because we live inside light coming from the background quasars, scientists are able to not only one or two the Milky Way, scientists probe the halo’s material. [NASA, ESA, and E. Wheatley (STScI)] sightlines, but over 40,” cannot easily interpret explained Lehner. “This the signature of our own galaxy’s two galaxies are quite similar. The is groundbreaking for capturing halo. However, they believe the two galaxies are on a collision the complexity of a galaxy halo halos of Andromeda and the Milky course, and will merge to form a beyond our own Milky Way.” Way must be very similar since these giant elliptical galaxy beginning In fact, Andromeda is the only gal- axy in the universe his diagram shows the light from for which this experi- T a background quasar passing ment can be done through the vast, gaseous halo now, and only with around the neighboring Andromeda galaxy (M31), as spectroscopically Hubble. Only with an measured by the Hubble Space Tele- ultraviolet-sensitive scope. The colored regions show ab- future space tele- sorption from two components that scope will scientists make up the halo. For ionized sili- be able to routinely con, a significant absorption is undertake this type shown in both plots. The more of experiment be- highly ionized carbon is absorbed by yond the approxi- only one component. Astronomers mately 30 galaxies can tell the two components apart comprising the Local because their line-of-sight motions, Group. “So Project known as radial velocity, cause a AMIGA has also given Doppler shift that changes the wavelength of light being absorbed. us a glimpse of the [NASA, ESA, and E. Wheatley (STScI)] future,” concluded Lehner. !

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www.newmoontelescopes.com [email protected] anthropocene EN_l'Astrofilo 28/10/2020 17:54 Page 24

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The Anthropoce an interstellar

by Michele Ferrara revised by Damian G. Allis NASA Solar System Ambassador

It seems incredible, but in an age when n the next few years, we will be able to analyze the atmospheres of the humans communicated remotely using Inearest exoplanets and understand if horseback couriers, carrier pigeons, fires they contain molecules consistent with the presence of life. Perhaps in those at- and mirrors, the first signals were al- mospheres, it will also be possible to recognize “pollutants,” gases not pro- ready being transmitted into space. The duced by natural processes that could Roman, Chinese and Spanish empires be the result of activities associated with particularly advanced and intelli- unwittingly added traces of their exis- gent life forms. Regardless of the com- tence to the light reflected from the position of each atmosphere, any ob- servation will provide a snapshot dat- Earth, and we cannot entirely exclude ing back to the moment when the light that those traces have already been no- collected by our instruments left the source. Theoretically, that light, prop- ticed by an extraterrestrial civilization. erly analyzed, can tell us if there is an

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ATMOSPHERIC POLLUTION 25 cene as messenger

he atmosphere advanced civilization on a particular planet that atmospheres polluted over a longer T is the calling and if they are at some level of develop- period of time will be recognizable at card of the Earth. ment similar to some level of ours over the greater distances from the Earth compared To the eyes of a course of our history. It is understandable to those in which pollution has only re- distant observer, cently begun, the periods in as the light that which it appears carries traces of most polluted may gases of non- be evident. Today natural origin it is very much pol- luted, and one of will have trav- the most worrying eled for longer. pollutants is Observations of this type will be methane (CH4), the molecular geome- clearly limited try of which is rep- by the resolving resented alongside. power of the [Hamish Weir] i n s t r u m e n t s

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used (which, especially in the presence of this opportunity is not one-way. Pollution n this graph of low abundances, may not allow for the cor- of the Earth’s atmosphere is also de- Iglobal carbon rect distinction of gases), but also condi- tectable from other planetary systems and dioxide emissions tioned by our current models on the it would be interesting to know how far from the time of formation and evolution of planets and away that detection can occur, as that is the first Industrial Revolution, it can their atmospheres. Despite this, there is no the limit beyond which an alien observer be seen that that doubt that, in certain scenarios, specific can only detect the generic presence of life initial, intense molecules either cannot be produced by on our planet but not the presence of an period of atmos- natural processes or cannot persist in plan- evolved civilization. This is equivalent to pheric pollution etary atmospheres without the support of saying that, beyond such limit, it does not is negligible com- biological activities. There are no solid ar- make much sense looking for possible mes- pared to the guments to assert that the life present on sages intentionally sent to us. Understand- emissions of the other planets might have a totally different ing how far the light reflected from our last century. impact on their atmospheres compared to polluted atmosphere has gone can ulti- [CDIAC] the only case we know. Therefore, if an- mately improve the targeting of some SETI other civilization has evolved by polluting programs. its own atmosphere, our methods of in- To determine that distance, we must take vestigation should be able to discover it a trip through the Anthropocene. This (within certain limits, of course). Obviously, term (introduced in the 1980s by the US bi-

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Data: Luthi, D., et al.. 2008; Etheridge, D.M., et al. 2010; Vostok ice core data/J.R. Petit et al.; NOAA Mauna Loa CO2 record.

bove, the ologist Eugene Filmore Stoermer) indicates which conventionally began about 11,700 Achanges in CO2 the period within which the impact of years ago at the end of the Würm Glacia- in the atmosphere human activity on the environment pro- tion. The anthropogenic (man-made) envi- over the last duced effects that are unequivocally distin- ronmental changes recognizable in the 800,000 years. guishable from those produced by natural Holocene have different weights depend- Below, the changes in temperature phenomena and processes. The Anthro- ing on the aspects considered. Here we are since the beginning pocene de facto overlaps a more or less ex- essentially interested in identifying the his- of the Cambrian, tensive part of the Holocene, the most torical context in which human activity has when life was es- recent geological epoch (the last of the indisputably produced widespread and sentially aquatic. Quaternary) and the one we now live in, persistent atmospheric pollution. There is

Carolyn W. Snyder

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and fossil fuels considerably in- mpressive im- creased the presence of carbon Iages that testify dioxide and sulfur dioxide in the at- to the appalling mosphere. air pollution that All the molecules produced in large oppressed large urban centers in quantities by human activities in the first decades the last two and a half centuries of the Industrial would be clearly visible in the light Revolution. of our planet collected and ana- About 200 light lyzed by an observer placed at a years from Earth, maximum distance of about 250 the traces of light years. Within this radius there this scenario are are at least 200,000 stars, some of certainly recog- which could host planets suitable nizable. for the development of life. Even with a strict selection, for ex- ample considering only solar-type stars with an age of not less than

no doubt that, from planets a few tens of light years away, anomalous abundances of (for example) benzene, toluene, nitrogen oxides, carbon monoxide, carbon dioxide, methane and various metals would be eas- ily distinguishable. Some of these elements and chemical compounds began to be mas- sively released into the atmosphere start- ing with the first Industrial Revolution, begun in England in 1760 and driven by the improvement of the steam engine. In- evitably, the growing demand for wood

four billion years, there would still be thousands of targets to be explored with specific SETI pro- grams. Undoubtedly, the last two and a half cen- turies of industrialization have strongly character- ized the Anthropocene, but minor and more local-

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ining in Po- ized episodes may have played a non-neg- that continent. The methods used by the Mtosí, work of ligible role in the pollution of the atmos- Spaniards to extract silver from galena, the 1596 by Theodoor phere even in more remote times. Some mineral that most commonly contains it, de Bry. Cerro studies carried out in the last two decades were first its melting in open furnaces (in- Rico, near the Bo- have actually highlighted historical periods efficient and very polluting) and then its livian city of Po- during which human activities seriously amalgamation with mercury. This second tosí, was known as the “mountain contaminated the air, that eats men.” and not just on a conti- Alongside, colo- nental scale. One of nial drawings of those periods began in furnaces for 1532, with the defeat of melting silver the Incas by the conquis- (huayras) in the tadors led by Francisco Bolivian Andes. Pizarro. The occupiers began to massively ex- ploit the silver mines of some Peruvian and Bo- livian locations, start- ing the most significant industrial activity on

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civilization 450 t the begin- light years (or less) Aning of 2019, from Earth. Theo- one of the oldest retically yes, but furnaces used by only if it has much the Romans was found in the gar- more powerful in- dens of Palazzo vestigation instru- Corsini, located ments than ours. It in the center of is estimated that, Rome. [Archeolo- within a sphere of gia Viva, Roma space with a radius Events] of 450 light-years around the Earth, there are at least

technique, introduced forty years after the overthrow of the Inca Empire, consisted of reducing the galena ore to powder and adding mercury, which amalgamated with the silver and separated it from the waste material (a subsequent distillation allowed for the recovery of the silver). Both tech- niques had dramatic effects on the environ- ment, as galena is made up of almost 90% lead and only 1-2% silver. Consequently, the smelting and, above all, the pulveriza- tion of that mineral during the Spanish oc- cupation introduced increasing quantities of lead and other harmful elements into the South American atmosphere, to the point of making that long period of in- tense mining and related metallurgical ac- tivity easily recognizable in the ice cores extracted from the Quelccaya Ice Cap (Peru), the second largest glaciated area in the tropics. This glacial site is located about 800 km away from Cerro Rico de Potosí (Bo- livia), the largest silver mine in the world and the one that some studies indicate as the point of origin of the metals found in the Peruvian ice. The distance between the two locations gives an idea of the level of pollution that affected those territories in the second half of the sixteenth century (and even later). At this point it is legitimate to ask oneself whether the anthropogenic trace of lead relating to that period can be observed “today” by a hypothetical contemporary

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whole Middle Ages (not very polluting, from our point of view) and reach the centuries that saw the birth and expansion of the Roman Empire, in particu- lar the centuries in which Rome dominated the an- cient world with its pres- ence on three continents. Even that long Roman pe- riod was characterized by intense mining activity, aimed at obtaining both silver (often used to mint coins) and lead (used in plumbing, paints and vari- ous furnishings). The production of lead, extracted mainly on the Iberian Peninsula, the Balkans, and the territories etails of one million stars, which is an excessively of Ancient Greece and Asia Minor, reached Dthe furnace, large population for any SETI project that a peak of 80,000 tons per year during the provisionally wants to observe single targets in search of golden age of the Roman Empire (2nd cen- dated between tury A.D.), a quan- st rd the 1 and 3 tity comparable centuries A.D. to that reached [Archeologia Viva, Roma almost 2000 years Events] later during the Industrial Revolu- tion. In addition to lead and silver, the Romans also produced large quantities of cop- per (up to 15,000 tons per year), which they often bound to tin to obtain the most resistant bronze. All this mining and metallurgical unnatural signals sent to us after discover- industriousness, in addition to being pollut- ing the lead released into the atmosphere ing by itself, required a considerable con- by the Spanish Empire. sumption of wood and coal. Their combus- Can we now exclude even more ancient an- tion, producing the aforementioned carbon thropogenic traces, reaching even further dioxide and sulfur dioxide, must have left into space today? No, we cannot. On the even more clear traces than those of lead. contrary, it seems that these traces exist, Of these atmospheric pollutants from impe- and to find them we have to fly over the rial Rome, however, no detectable deposits

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Drilling (NEEM) project showed that, n this page, precisely at the developmental peak Osome snap- of those ancient civilizations, signifi- shots of the North cant quantities of greenhouse gases Greenland Eemian were produced, among which meth- Ice Drilling, the project that has ane stands out. Célia Julia Sapart, a given to numer- specialist in greenhouse gas emissions ous groups of re- and historical climate reconstruction, searchers the as well as the leader of the team that opportunity to conducted the study, said that “the study variations ice core data show that as far back as in climate and at- the time of the Roman Empire, human mospheric com- position. [NEEM can be found trapped in glaciers. This Project Office] is perhaps because, between 250 B.C. and 400 A.D., the European continent went through a phase with an unusu- ally warm climate, known in history as the “Roman Warm Period.” Nonethe- less, it is likely that for some centuries the atmosphere had shown anom- alous abundances of lead and anhy- drides. But even if this were not the case, there is certainly another indica- tor that may have signaled our pres- activities emitted enough methane gas to have had an impact on the methane signature of the entire at- mosphere,” hence globally. Since all this happened almost 2000 years ago, the anthropogenic mes- sage carried by the light reflected from the Earth has reached (over the centuries) all the stars up to almost 2000 light years away, which are es- timated to be about 50 million. Ac- cording to new estimates (June 2020) by astronomers at the University of ence to other civilizations at that same time: methane. Forest conversion for agriculture and livestock in the Roman Empire, to- gether with the simultaneous large expansion in China of areas cultivated for rice harvesting under the Han dy- nasty, started a forced increase in the abundance of methane in the atmos- phere. A study conducted in 2012 by a team of European and American re- searchers on ice cores extracted as part of the North Greenland Eemian Ice

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n this represen- British Columbia, produced with data from There are those who worry that our first Itation of the NASA’s Kepler mission, one Earth-like radio transmissions, theoretically having Milky Way, a planet could exist in the Milky Way for reached about 100 light years away (actu- green circle indi- every five Sun-like stars. G-type stars, those ally already dispersed in the background cates the region more similar to the Sun, are about 7% of noise of the universe), could inform other within which the the total. K-type stars, slightly smaller than intelligent life forms of our existence. As pollution of our atmosphere may the Sun but even more promising from an we have seen, the traces of ancient terres- have been ob- astrobiological point of view, are about trial civilizations have probably already served in the 13% of the total. According to these per- reached far beyond, and their involuntary last 2000 years. centages, within 2000 light years from message, which continues to whiz through [Robert Hurt Earth there could be 2 million planets sim- the Milky Way, is much easier to discover (SSC/JPL/Caltech)] ilar to ours. All uninhabited? than a faint radio wave. !

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34 SPACE CHRONICLES

Hubble captures crisp new image of Jupiter and Europa

by NASA/ESA

his latest image of Jupiter, taken by the NASA/ESA Researchers say the Great Hubble Space Telescope on 25 August 2020, was Red Spot now measures T captured when the planet was 653 million kilome- about 15,800 kilometres tres from Earth. Hubble’s sharp view is giving researchers across, big enough to swal- an updated weather report on the monster planet’s tur- low the Earth. The super- bulent atmosphere, including a remarkable new storm storm is still shrinking, as brewing, and a cousin of the Great Red Spot changing noted in telescopic observa- colour — again. The new image also features Jupiter’s icy tions dating back to 1930, moon Europa. but its rate of shrinkage ap- A unique and exciting detail of Hubble’s new snapshot pears to have slowed. The rea- appears at mid-northern latitudes as a bright, white, son for its dwindling size is a stretched-out storm moving at 560 kilometres per hour. complete mystery. This single plume erupted on 18 August 2020 and an- Researchers are noticing that an- other has since appeared. other feature has changed: the While it’s common for storms to pop up in this region, Oval BA, nicknamed by astronomers often several at once, this particular disturbance appears as Red Spot Jr., which appears just to have more structure behind it than observed in previ- below the Great Red Spot in this ous storms. Trailing behind the plume are small, coun- image. For the past few years, Red Spot terclockwise dark clumps also not witnessed in the past. Jr. has been fading in colour to its original Researchers speculate this may be the beginning of a shade of white after appearing red in 2006. longer-lasting northern hemisphere spot, perhaps to However, now the core of this storm appears rival the legendary Great Red Spot that dominates the to be darkening to a reddish hue. This could hint southern hemisphere. Hubble shows that the Great Red that Red Spot Jr. is on its way to reverting to a Spot, rolling counterclockwise in the planet’s southern colour more similar to that of its cousin. hemisphere, is ploughing into the clouds ahead of it, Hubble’s image shows that Jupiter is clearing out its forming a cascade of white and beige ribbons. The Great higher-altitude white clouds, especially along the Red Spot is currently an exceptionally rich red colour, planet’s equator, which is enveloped in an orangish hy- with its core and outermost band appearing deeper red. drocarbon smog.

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36 SPACE CHRONICLES

Jupiter’s icy moon Europa is visible gets in the search for habitable multiwavelength observation in to the left of the gas giant. Europa worlds beyond Earth. In 2013 it was A ultraviolet/visible/near-infrared is already thought to harbour a liq- announced that the Hubble Space light of Jupiter obtained by the uid ocean beneath its icy crust, mak- Telescope discovered water vapour NASA/ESA Hubble Space Telescope ing this moon one of the main tar- erupting from the frigid surface of on 25 August 2020 is giving re- Europa, in one or searchers an entirely new view of more localised the giant planet. [NASA, ESA, A. plumes near its Simon (Goddard Space Flight Center), south pole. ESA’s and M. H. Wong (University of Cali- JUpiter ICy moons fornia, Berkeley) and the OPAL team] Explorer, a mission planned for launch near-infrared light of Jupiter on 25 in 2022, aims to ex- August 2020, which is giving re- plore both Jupiter searchers an entirely new view of and three of its the giant planet. Hubble’s near in- largest moons: frared imaging, combined with ul- Ganymede, Cal- traviolet views, provides a unique listo, and Europa. panchromatic look that offers in- his video presents two new views of Jupiter taken by Hubble also cap- sights into the altitude and distri- T the NASA/ESA Hubble Space Telescope. [NASA, ESA, tured a new multi- bution of the planet’s haze and par- A. Simon (Goddard Space Flight Center), and M. H. Wong w a v e l e n g t h ticles. This complements Hubble’s (University of California, Berkeley), the OPAL team, and M. Kornmesser (ESA/Hubble)] observation in ul- visible-light picture that shows the traviolet/visible/ ever-changing cloud patterns. !

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Science in School aims to promote inspir- ing science teaching by encouraging communica- tion between teachers, scientists, and everyone else involved in European sci- ence education. Science in School is published by EIROforum, a collaboration between eight European intergovernmen- tal scientific research organisations, of which ESO is a member. The journal addresses science teaching both across Europe and across disciplines: highlighting the best in teaching and cutting-edge research. Read more about Science in School at: http://www.scienceinschool.org/ ET radio EN_l'Astrofilo 28/10/2020 17:56 Page 38

38 ASTROBIOLOGY

Good morning Earth. This is ET radio!

by Michele Ferrara revised by Damian G. Allis NASA Solar System Ambassador

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ASTROBIOLOGY 39

round view The patchy search for alien civilizations in the Milky Way Gof one of the 256 grids, each continues tirelessly. Nearly all surveys are focused on radio made up of 16 spider-shaped an- waves, and will continue to be in the future, thanks largely tennas, that make to the planning of gigantic networks of radio telescopes, up the Murchison Widefield Array such as the Square Kilometer Array, soon to at the Murchison Radio-astronomy be built in Australia and South Africa. On Observatory (MRO), 800 km the contrary, the search for alien signals north of Perth, in the visible light domain is rather Australia. [Drag- onfly Media] neglected, which could be an error. n the September-October issue, we re- flected on the search for alien tech- Inological civilizations, coming to the conclusion that we are very far from having the necessary in- struments in place to under- stand if, in the Milky Way, there are other forms of

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life aware of the cosmos that surrounds 23 January 2018, the two Australian re- he vast ex- them. We have seen that, statistically, it is searchers tuned the MWA to the 98-128 T panses of necessary to observe or “listen to” hundreds MHz frequency range and aimed it at an Western Australia of millions of stars to have a minimal chance area of sky about 400 square degrees wide, are perfect for of recording any unnatural signal. Obvi- centered on the constellation Vela. That radio astronomy. In the fore- ously, the situation has not changed in the range of frequencies falls within the FM ground, one of last two months, but a small step has been (frequency modulation) band, typically used the 256 MWA taken, as reported in Publications of the on Earth for radio broadcasting. When we grids, spread over Astronomical Society several square of Australia (PASA), kilometers. [Pete where the results of a Wheeler, ICRAR] survey that deserves On the left, other to be commented on installations, have appeared. with researcher This umpteenth SETI Nichole Barry study was conducted present in the by Chenoa Tremblay grid, making it possible to esti- and Steven Tingay mate the size of (Curtin University, the antennas. Australia) using the [Ruby Byrne] Murchison Widefield Array (MWA) radio telescope of the Murchison Radio-as- tronomy Observa- tory. Between 5 and

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ASTROBIOLOGY 41

he authors of listen to our favorite T the survey radio station, we are discussed in this tuned to a frequency article: Steven in the FM band, and Tingay and probably to one used Chenoa Tremblay. by Tremblay and Tin- [Curtin Univer- sity, ICRAR] gay to search for alien broadcasts. The two researchers simulta- neously listened to over 3,000 channels with a resolution of 10 kHz, sufficient to distinguish any pow- erful alien transmis- sion sent from the planets closest to us among those in orbit around the approxi- mately 10 million stars framed by the MWA. around the constellation of Vela for 17 Each single observation (listening) of the en- hours, looking more than 100 times broader tire probed area lasted only 5 minutes, for and deeper than ever before.” a total integration time of 17 hours. How- Despite this, all the channels listened to ever small this period may seem, the survey were silent. Here is what Tingay said about conducted by Tremblay and Tingay is to this, not at all surprised by the negative re- date the deepest and most extensive carried sult: “With this dataset, we found no tech- out in low frequency. As Trembley herself nosignatures — no sign of intelligent life. As pointed out: “The MWA is a unique tele- Douglas Adams noted in The Hitchhiker’s scope, with an extraordinarily wide field-of- Guide to the Galaxy, ‘space is big, really big’. view that allows us to observe millions of And even though this was a really big study, stars simultaneously. We observed the sky the amount of space we looked at was the equivalent of trying to find something in the Earth’s oceans but only searching a vol- ume of water equivalent to a large back- yard swimming pool. Since we can’t really assume how possible alien civilizations might utilize technology, we need to search in many different ways. Although there is a long way to go in the search for extraterres- trial intelligence, telescopes such as the MWA will continue to push the limits — we have to keep looking.” Tingay is not new to these performances. Previously, he had probed similar frequency ranges by pointing the MWA towards the Galactic Center and the Galactic Anticenter regions, both with the same results: ab- solute silence (excluding interference of ter- restrial origin). In fact, although the MWA has been installed in a remote place (Boolardy, Western Australia) and is pro- tected from radio signals emitted by inhab-

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phase are known. y modulating If we listened to a B a carrier radio radio station that wave with a suit- transmits only the ably produced carrier, we could signal, we can have two types at most hear a sin- of resulting sig- gle note or a con- nals: one modu- tinuous noise. lated in frequency Instead, we hear (FM) and one voices and music, modulated in am- and this is because plitude (AM). the carrier has Tremblay and been modulated Tingay searched with the electrical for FM signals signals generated from a large re- by the transducer. gion of the sky The addition of in- centered on the constellation formation causes Vela, but with the regular sinu- negative results. soidal shape of Below, an anima- the carrier to un- tion showing the dergo a change in two types of amplitude (AM = radio signals. amplitude modu- lation) or in fre- quency (the afore- mentioned FM = ited centers, interference may nevertheless frequency modulation). The signal thus ob- occur that researchers must remove with ap- tained is amplified and radiated through an propriate tricks. However, interference as a antenna in the form of electromagnetic ra- whole limits the potential of the instrument diation. by more than 30%. Therefore, one wonders AM was the first method used to transmit the reason for looking for a hypothetical radio programs, but achieving quality recep- alien transmission precisely in the FM band, tion was often difficult due to adverse occupied by thousands of radio stations weather conditions or sources of electric (mostly commercial), with all of the compli- fields of various kinds that produced alter- cations that this entails. To understand that choice, we must start from the very nature of radio waves. They are a subset of the electromagnetic spectrum and, by conven- tion, are divided into bands. Depending on the bands used, radio waves can be em- ployed to transmit data, sounds, images and any other element that can be converted with a transducer (encoder, microphone, camera, etc.) into electrical signals of vari- able amplitude. These electrical signals are, de facto, the information you want to trans- mit. To transmit it, however, it is necessary to generate the so-called “carrier wave” (or simply “carrier”) with an oscillating circuit, of which the frequency, amplitude and

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nfographic of ations in the amplitude of the sent radio considered a universal means of investiga- I the electromag- wave. A valid alternative was devised in the tion and communication. We don’t know netic spectrum, 1930s by the American engineer Edwin why Tremblay and Tingay decided to center which includes Howard Armstrong, who developed the fre- their latest survey on the constellation Vela. the levels of pen- quency modulation technique that is both In their article published in PASA, they em- etration of the much less subject to interference and more phasize the presence in this region of six various forms of radiation in the efficient in various applications. This is why known exoplanets, at which their listening Earth’s atmos- any alien technological civilization could be was particularly attentive. However, as al- phere. expected to choose to broadcast on FM ready mentioned, the survey included about rather than other radio bands. This, of 10 million stars, and therefore likely millions course, is a terrestrial opinion, although the of other unknown exoplanets. It would not electromagnetic spectrum in general can be have been easy to find the source of any FM

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signal not directly attributable to that handful of known ex- oplanets. Tuning into the right channel, identifying the trans- mitter in space, and receiving the message are all actions that require a precise level of cognitive and technological development that the broad- caster (the alien civilization) should consider typical of the receiver (us). How could the alien civilization be certain of our ability to perform those actions? Why should anyone who takes the initiative to attempt a contact choose a path that re- quires the possible interlocu- tor to use complex techniques and processes so that the mes- sage sent is received and un- derstood? Furthermore, con- sidering the immense distance that would surely divide two galactic technological civiliza- tions, and the very long times that would then elapse be- tween each back and forth, would it even make sense to start a conversation? Each reply to a previous message could find an interlocutor with ideas and intentions dif- ferent from the original ones. They may not even know the previous contents of the con- versation or no longer be able to recognize our messages. Those who deal with these is- sues inevitably ask themselves why the members of a tech- nological civilization should seek contact (active or passive, it does not matter) with a sim- ilar civilization on a very dis- tant planet. The answer is obvious: to understand if they are alone in their galaxy or in the universe. Although we hu- mans inhabit this wonderful planet in the company of

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n the previous about nine million other living species (of messages of that type arriving at Earth, hop- I page, the fa- which only 14% are identified), we feel ing they will be receivable with our instru- mous message alone as if we were a single organism de- ments. If they were sent with more from Arecibo sent tached from all others. Discovering around advanced technologies than ours, they to unknown be- another star someone more similar to us could go unnoticed or unheard. Our own ings on Novem- than other terrestrial animals and plants technological development does not trend ber 16, 1974. Its content is exces- whould mitigate our sense of solitude, as towards the kind of simplified messaging sively anthro- well as have heavy implications of a scien- that would be most desirable for a success- pocentric and tific, philosophical and religious nature. ful contact attempt. Therefore, is it not per- childish. After Based on the principle of mediocrity (dis- haps more reasonable to assume that those that naive under- cussed in the July-August issue), this senti- who decide to send a message into space taking, another ment should be typical of all technological would want to do so in a part of the elec- thirty messages civilizations, or at least those that attempt tromagnetic spectrum that is essential to in- were sent with contact. Therefore, given the insuperable telligent life – so essential as to be the other antennas to difficulties of an interstellar conversation reason for a species’ basic awareness of the individual stars. and considering that the primary purpose universe itself? We obviously refer to the One of them, the should be to simply be sure of the existence light visible to the eyes of ourselves and Altair (Morimoto of the other, the content of the message other evolved animals, light that generally − Hirabayashi) Message, has al- sent or expected could be the equivalent of occupies the 400-700 nanometer range of ready reached its a simple “you are not alone” or “we are the electromagnetic spectrum. It is difficult destination. The here too.” More than anything else, it to imagine life forms that look at the stars, rest will reach should be an altruistic act of one civilization and therefore the universe, in a totally dif- different stars be- towards another civilization, of which the ferent light than our own. For example, can tween 2022 and sender of the message sensed the existence intelligent life develop on a planet by see- 2450. by analyzing a planetary atmosphere. Since ing the environment in which it evolves in we are not yet able to let others know that gamma, X or UV rays? A simple “no” may they are not alone, we just have to look for be enough. Similarly, it could not do so by

hypothetical A light curve of a star in which an artificial signal has been added, here represented by short peaks emerging from the scatter of the measurements. In a real scenario, the intensity and duration of the peaks, as well as the intervals that separate them, could hide an alien message.

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seeing radio waves or microwaves emitted also in color) of so-called visible light. That fter seven by everything that exists on the rocky sur- same alien civilization could also reason- A years of de- face of its planet of origin, as inanimate ably assume that, if we are curious enough, sign and proto- objects in a terrestrial-like environment do we would have already invented the tele- typing, the Inter- not habitually emit such radiation. In the scopes and other devices useful for record- national Center first case, life would not exist; in the second ing starlight, and that we are therefore for Radio Astron- omy Research case, it would not have the slightest aware- able to perceive small variations in the light (ICRAR) has com- ness of what surrounds it (although, at radiation arriving at our planet. On the pleted prepara- most, an exception could be made for in- contrary, ET would have no certainty of our tions for the con- frared radiation). knowledge of radio waves, which are not struction of SKA, It is, therefore, not a gamble to say that the as essential to the evolution of intelligent which will begin only certainty an alien civilization could life. So why look for frequency modulation in 2021 and will have about us is that we are able to distin- or in radio bands at all? The obstinacy of give new impetus guish variations in intensity (and perhaps most SETI projects in investigating the ra- to SETI projects.

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advanced civilization may have already built it. Having enough power available, ET would be able to send light pulses into space that would add to the brightness of the parent star, causing small variations in magni- tude in the entire visible spec- trum (white light) or in certain colors. By suitably modulating the impulses, a sequence “easily” dis- tinguishable from the variations attributable to natural phenom- ena would be generated. What can we expect to see in that star’s light curve? Probably short and simple numerical sequences (it is reasonable that ET knows how to count), represented by impulses of varying duration, intensity and amplitude. If the sole purpose of the message is to inform us that we are not alone, the beginning of some basic numerical se- quences may be enough, where each subsequent number is repre- sented with light pulses of a du- ration or intensity proportionally higher than the previous one. We can perhaps expect the most basic 1, 2, 3, 4, 5, 6, 7... or a se- quence of the prime numbers 2, 3, 5, 7, 11, 13, 17... or the Fi- bonacci sequence 1, 1, 2, 3, 5, 8, 13... all probably known by a technological alien civilization. The preference of one sequence over the others may depend on dio domain is truly amazing. Perhaps it the amount of energy required to produce would be preferable to launch more diver- and keep the signal transmitted for a long sified surveys, massively including visible time. Intuitively, higher numbers would re- frequencies in these studies − a choice that quire more energy, and for this reason the could restore meaning to the dozens of op- sequences might appear short but re- tical telescopes that lie unused in less ad- peated. Long sequences, as well as being vanced professional observatories. excessively expensive, might also be less An alien civilization could send a periodic legible. Curiously, the duration of the inter- message in visible light through powerful vals between successive pulses could also lasers powered by large photovoltaic sys- be revealing, representing, for example, it- tems much more efficient than ours. self a numerical sequence. From a conceptual point of view, we earth- Waiting for more targeted SETI projects, lings already have an idea of how to make let’s turn on the radio − you never know a transmitter of that type. A slightly more what might happen! !

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A spectacular supernova time-lapse

by NASA/ESA

he NASA/ESA’s Hubble Space questions about our Universe’s very galaxy NGC 2525, which is located in Telescope has tracked the fad- nature. The supernova, formally the constellation of Puppis in the T ing light of a supernova in the known as SN2018gv, was first spot- Southern Hemisphere. spiral galaxy NGC 2525, located 70 ted in mid-January 2018. Hubble The supernova is captured by Hub- million light-years away. Super- began observing the brilliant bright- ble in exquisite detail within this novae like this one can be used as ness of the supernova in February galaxy in the left portion of the cosmic tape measures, allowing as- 2018 as part of the research pro- image. It appears as a very bright tronomers to calculate the distance gram led by lead researcher and star located on the outer edge of to their galaxies. Hubble captured Nobel Laureate Adam Riess of the one of its beautiful swirling spiral these images as part of one of its Space Telescope Science Institute arms. This new and unique time- major investigations, measuring the (STScI) and Johns Hopkins Univer- lapse of Hubble images created by expansion rate of the Universe, sity, in Baltimore, USA. The Hubble the ESA/Hubble team shows the which can help answer fundamental images center on the barred spiral once bright supernova initially out-

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ictured in the background is part of the captivating P galaxy NGC 2525 (above). Located nearly 70 million light-years from Earth, this galaxy is part of the constella- tion of Puppis in the southern hemisphere. Together with the Carina and the Vela constellations, it makes up an image of the Argo from ancient greek mythology. On the left, a brilliant supernova is clearly visible in the image. The supernova is formally known as SN2018gv and was first spotted in mid-January 2018. [ESA/Hubble & NASA, A. Riess and the SH0ES team. Ack: Mahdi Zamani]

shining the brightest stars in the novae are powerful explosions and carbon together in a matter of galaxy, before fading into obscurity which mark the end of a star’s life. seconds. The energy released tears during the year of observations. The type of supernova seen in these the star apart in a violent explosion, This time-lapse consists of observa- images, known as a Type Ia super- ejecting matter at speeds up to 6% tions taken over the course of one nova, originate from a white dwarf the speed of light and emitting year, from February 2018 to Febru- in a close binary system accreting huge amounts of radiation. ary 2019. material from its companion star. If Type Ia supernovae consistently “No Earthly fireworks display can the white dwarf reaches a critical reach a peak brightness of 5 billion compete with this supernova, cap- mass (1.44 times the mass of our times brighter than our Sun before tured in its fading glory by the Hub- Sun), its core becomes hot enough fading over time. ble Space Telescope,” shared Riess to ignite carbon fusion, triggering Because supernovae of this type of this new time-lapse of the super- a thermonuclear runaway process produce this fixed brightness, they nova explosion in NGC 2525. Super- that fuses large amounts of oxygen are useful tools for astronomers,

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known as ‘standard can- dles’, which act as cosmic tape measures. Knowing the actual brightness of the supernova and observ- ing its apparent brightness in the sky, astronomers can calculate the distance to these grand spectacles and therefore their galaxies. Riess and his team com- bined the distance meas- urements from the su- pernovae with distances calculated using variable stars known as Cepheid variables. Cepheid vari- ables pulsate in size, caus- ing periodic changes in brightness. As this period is directly related to the star’s brightness, astronomers can calculate the distance sion rate of the Uni- ictured here is the region to them: allowing them to act as another standard can- verse, known as the P surround-ing NGC 2525. Lo- dle in the cosmic distance ladder. Riess and his team are Hubble constant. This cated nearly 70 million light- interested in accurately measuring the distance to these value accounts for how years from Earth, this galaxy is galaxies since it helps them better constrain the expan- fast the Universe is ex- part of the constellation of panding de- Puppis in the southern hemi- pending on its sphere. [ESA/Hubble, Digitized distance from Sky Survey 2. Ack: D. De Martin] us, with more distant galaxies moving faster away from us. Since it launched, Hubble Space Telescope has helped dramatically improve the precision of the Hubble constant. Results from the same observ- ing program led by Riess have now reduced the uncertainty of their measurement of the Hubble constant to an unprecedented 1.9%. Further measurements of NGC 2525 will con- tribute to their goal of reducing the uncertainty down to 1%, pinpointing how fast the Universe is expanding. his video shows a unique time-lapse of the supernova in galaxy A more accurate Hubble constant may uncover T NGC 2525. The supernova is captured by Hubble in exquisite de- clues about the invisible dark matter and myste- tail within this galaxy in the lower left portion of the frame. It ap- rious dark energy, responsible for accelerating pears as a very bright star located on the outer edge of one of its the Universe’s rate of expansion. Together this beautiful swirling spiral arms. This new and unique time-lapse of information can help us understand the history Hubble images shows the once bright supernova initially outshining and future fate of our Universe. A supermassive the brightest stars in the galaxy, before fading into obscurity dur- black hole is also known to be lurking at the cen- ing the telescope’s observations. This time-lapse consists of obser- tre of NGC 2525. Nearly every galaxy contains a vations taken over the course of one year, from February 2018 to supermassive black hole, which can range in February 2019. [ESA/Hubble & NASA, M. Kornmesser, M. Zamani, mass from hundreds of thousands to billions of A. Riess and the SH0ES team] times the mass of the Sun. !

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Monte Bianco Cableways: the dream of bringing man closer to the mountains and the sky.

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