Sterrekunde

Kan die James Webb-ruimteteleskoop biosignale op eksoplanete opspoor?

Kan die James Webb-ruimteteleskoop biosignale op eksoplanete opspoor?


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Die James Webb-ruimteteleskoop (JWST) wat na verwagting in 2018 van stapel gestuur word, sal ons 'n beter oorsig van eksoplanete gee, maar sal dit voldoende wees om tekens van lewe op ten minste sommige van daardie wêrelde op te spoor?

'N Goeie antwoord gee 'n skatting van die vermoëns van die James Webb-ruimteteleskoop om atmosferiese data op te spoor wat relevant is vir die teenwoordigheid van lewe.

Die voorkeurantwoord sal ook 'n analise insluit van wat dit sal neem om met 'n ordentlike mate van vertroue te sê dat die lewe op 'n eksoplanet bestaan ​​en of JWST daartoe in staat is al dan nie.


Volgens wat ek verstaan, sou James Webb, indien dit saam met 'n suksesvolle sterrekleur (wat by MIT ontwikkel word) gebruik word, in staat wees om naby op te sien in planete wat in die omgewing van sterre wentel. Dit is egter onwaarskynlik dat 'n goeie atmosferiese spektra van hierdie planete direk verkry word (vanaf die IR-emissie van die planeet se swartliggaam). Waarvoor ons moet hoop, is dat TESS, wat in 2017 sou opgaan, 'n paar sterre in die omgewing met planete sou vind. Dan sal James Webb in staat wees om na atmosferiese absorberingslyne te soek van sterrelig wat deur die atmosfeer van 'n planeet beweeg tydens vervoer. Hierdie metode kan steeds beperk word tot groot (Jupiter grootte) planete. In 'n ideale situasie (sê na die absorptielyne van 'n super-aarde) is daar baie "bio-handtekeninge", maar een van die maklikste om op te spoor is 'n osoonlyn in die infrarooi. Op sigself sou dit geen bewys wees nie, alhoewel daar 'n voortdurende aanvullende bron van O2 in die atmosfeer moet wees om die O3 te handhaaf. As daar ook metaan gevind kan word, kan ons met reg BAIE opgewonde raak omdat metaan en suurstof nie baie goed bestaan ​​nie.


NASA se volgende ruimteteleskoop kan besonderhede oor die TRAPPIST-1-planete onthul, maar daar is een probleem

Die James Webb-ruimteteleskoop (Webb) kan kritieke inligting versamel oor die atmosfeer van planete in die TRAPPIST-1 planetêre stelsel, maar die grootste struikelblok kan wolke wees, het een nuwe studie bevind.

Die soeke na lewe en wêrelde wat die lewe soos ons dit hier op aarde teoreties kan ondersteun, hang af van die mens se vermoë om uithoeke van die kosmos ver van die huis te verken en te bestudeer. Webb, wat in 2021 begin, het vier hoofdoelstellings: om lig op te spoor van die eerste sterre en sterrestelsels wat in die heelal gevorm het, om planetêre stelsels te bestudeer, om die vorming van sterre en planetêre stelsels te ondersoek, en om die oorsprong van die lewe te ondersoek. Wetenskaplikes het gehoop dat die teleskoop, deur hierdie doelstellings na te streef, ook die soeke na die lewe kan bevorder.

Wetenskaplikes stel veral belang in die TRAPPIST-1-stelsel, hoewel simulasies in vorige studies het getoon dat die meeste wêrelde in hierdie stelsel is waarskynlik onbewoonbaar; een & mdash TRAPPIST-1e & mdash kan vloeibare water huisves en in staat wees om die lewe te onderhou soos ons dit ken.

Navorsers in hierdie nuwe studie het simulasies uitgevoer met behulp van die TRAPPIST-1-stelsel en 'n planetêre stelsel 39 ligjare verderop wat sewe bevestigde eksoplanete bevat wat 'n ultrakoele ster en mdash wentel as 'n toetsgrond vir die potensiële vermoëns van die teleskoop. Hulle het gevind dat, teoreties, Webb die atmosfeer van al sewe wêrelde in die stelsel in minder as tien deurgange kon opspoor, of voor sy gasheerster verbygaan.

Die span, gelei deur Jacob Lustig-Yaeger, 'n doktorale student in sterrekunde aan die Universiteit van Washington, het bevind dat die teleskoop dit kan doen met behulp van 'n instrument aan boord genaamd die Near Infrared Spectrograph.

Sterrekundiges bespeur en bestudeer eksoplanete soos dié in TRAPPIST-1 deur waar te neem wanneer hulle hul ster vervoer. Deur die lig te bestudeer wat deur 'n planeet se atmosfeer gaan terwyl die planeet sy ster deurlaat, kan wetenskaplikes variasies in kleur en golflengte raaksien wat ontstaan ​​wanneer lig deur verskillende gasse in die atmosfeer van die planeet beweeg.

"Aangesien elke gas 'n unieke 'spektrale vingerafdruk' het, kan ons dit identifiseer en die samestelling van die eksoplanet se atmosfeer begin saamstel," het Lustig-Yaeger gesê. in 'n verklaring gesê.

Wetenskaplikes stel veral belang in die TRAPPIST-1-stelsel, hoewel simulasies in vorige studies het getoon dat die meeste wêrelde in hierdie stelsel is waarskynlik onbewoonbaar; een & mdash TRAPPIST-1e & mdash kan vloeibare water huisves en in staat wees om die lewe te onderhou soos ons dit ken.

Die span het egter bevind dat, hoewel Webb die atmosfeer van al die planete in TRAPPIST-1 binne die eerste operasiejaar van die teleskoop kon opspoor en bestudeer, dit baie belemmer sou word deur wolke. "Ons vind dat transmissiespektroskopie met die naby-infrarooi spectrograaf-prisma optimaal is om aardse, CO2-bevattende atmosferes op te spoor, moontlik in minder as 10 deurgange vir al sewe TRAPPIST-1-planete, as hulle nie aerosole op hoë hoogte het nie, of wolke, die studie se opsomming state.

Alhoewel dit minder as tien deurgange van Webb kan neem om 'n atmosfeer in 'n wolkvrye wêreld in die stelsel op te spoor, kan dit volgens die verklaring meer as 30 deurgange neem om 'n planeet te vind wat deur dik wolke omhul word. Maar hoewel wolke (wat wel of nie in die TRAPPIST-1-wêrelde bestaan ​​nie) 'n uitdaging kan bied, is dit nie 'n volledige versperring nie.

"Selfs in die geval van realistiese wolke op groot hoogte, kan die James Webb-teleskoop steeds die teenwoordigheid van atmosfeer en mdash opspoor wat voorheen nie bekend was nie," het Lustig-Yaeger in dieselfde verklaring gesê.

Wetenskaplikes moet nog bevestig watter, indien enige, van die planete in TRAPPIST-1 atmosfeer het. Webb kon die teenwoordigheid van enige atmosfeer verifieer en selfs die samestelling daarvan ontleed.

"Daar is tans 'n groot vraag in die veld: of hierdie planete selfs atmosfeer het, veral die binneste planete," het Lustig-Yaeger gesê. "Sodra ons bevestig het dat daar atmosferes is, wat kan ons dan leer oor die atmosfeer van elke planeet en die molekules waaruit dit bestaan, aanpas?"


Nuwe metode om atmosfeer op rotsagtige eksoplanete te vind met die Webb-ruimteteleskoop

Die indruk van hierdie kunstenaar toon 'n rotsagtige exoplanet met 'n skerp, bewolkte atmosfeer wat om 'n rooi dwergster wentel. Sterrekundiges het 'n nuwe metode geïdentifiseer wat Webb in staat stel om binne 'n paar uur waarnemingstyd 'n eksoplanet se atmosfeer op te spoor. Krediet: L. Hustak en J. Olmsted (STScI)

Wanneer die NASA se James Webb-ruimteteleskoop in 2021 van stapel gestuur word, sal die bestudering van eksoplanete — planete wat om sterre in die rondte wentel - een van die mees verwagte bydraes tot die sterrekunde wees. Van die dringendste vrae in die eksoplanetwetenskap is: Kan 'n klein, rotsagtige eksoplaneet wat naby 'n rooi dwergster wentel, 'n atmosfeer hou?

In 'n reeks van vier referate in die Astrofisiese joernaal, stel 'n span sterrekundiges 'n nuwe metode voor om Webb te gebruik om vas te stel of 'n rotsagtige exoplanet 'n atmosfeer het. Die tegniek, wat behels dat die temperatuur van die planeet gemeet word terwyl dit agter sy ster verbygaan en dan weer in sig kom, is aansienlik vinniger as meer tradisionele metodes vir atmosferiese opsporing, soos transmissiespektroskopie.

"Ons vind dat Webb die afwesigheid of afwesigheid van 'n atmosfeer rondom 'n dosyn bekende rotsagtige eksoplanete met minder as tien uur waarnemingstyd per planeet maklik kan aflei," het Jacob Bean van die Universiteit van Chicago, 'n medeskrywer van drie van die vraestelle.

Sterrekundiges stel om verskeie redes veral daarin belang dat eksoplanete om rooi dwergsterre wentel. Hierdie sterre, wat kleiner en koeler is as die son, is die mees algemene tipe sterre in ons sterrestelsel. Ook omdat 'n rooi dwerg klein is, sal dit lyk asof 'n planeet wat daarvoor verbygaan 'n groter fraksie van die ster se lig blokkeer as wanneer die ster groter sou wees, soos ons son. Dit maak die planeet wat om 'n rooi dwerg wentel makliker om dit op te spoor deur middel van hierdie & # 8220transit & # 8221 tegniek.

Rooi dwerge produseer ook baie minder hitte as ons son, dus om 'n bewoonbare temperatuur te geniet, sal 'n planeet baie naby 'n rooi dwergster moet wentel. Om in die bewoonbare gebied te wees - die gebied rondom die ster waar vloeibare water op 'n planeet en sy oppervlak kan bestaan ​​- moet die planeet baie nader aan die ster wentel as wat Mercurius aan die son is. As gevolg hiervan sal dit die ster meer gereeld vervoer, wat herhaalde waarnemings vergemaklik.

Maar 'n planeet wat so naby 'n rooi dwerg wentel, word onder moeilike omstandighede onderwerp. Jong rooi dwerge is baie aktief en blaas groot fakkels en plasma-uitbarstings uit. Die ster stuur ook 'n sterk wind van gelaaide deeltjies uit. Al hierdie effekte kan moontlik die atmosfeer van 'n planeet wegsoek en 'n kaal rots agterlaat.

"Atmosferiese verlies is die grootste eksistensiële bedreiging vir die bewoonbaarheid van planete," het Bean gesê.

'N Ander belangrike kenmerk van eksoplanete wat naby rooi dwerge wentel, staan ​​sentraal in die nuwe tegniek: daar word verwag dat hulle getyvergrendeld sal wees, wat beteken dat hulle 'n permanente dag- en nagkant het. As gevolg hiervan sien ons verskillende fases van die planeet op verskillende punte in sy baan. Wanneer dit die gesig van die ster kruis, sien ons net die planeet se nagkant. Maar as dit op die punt staan ​​om agter die ster aan te kruis ('n gebeurtenis wat bekend staan ​​as 'n sekondêre verduistering), of net agter die ster te voorskyn kom, kan ons die dagkyk waarneem.

As 'n atmosfeer nie aan 'n rotsagtige exoplanet is nie, sal die dagkant daarvan baie warm wees, net soos ons dit met die maan of kwik sien. As 'n rotsagtige eksoplanet egter 'n atmosfeer het, sal die atmosfeer na verwagting die temperatuur langs die dag wat Webb sou meet, verlaag. Dit kan dit op twee maniere doen. 'N Dik atmosfeer kan hitte van die dag na die nag deur winde vervoer. 'N Dunner atmosfeer kan steeds wolke huisves, wat 'n deel van die inkomende sterlig weerspieël en sodoende die temperatuur van die planeet en die dag se kant verlaag.

'Wanneer jy 'n atmosfeer toevoeg, gaan jy die temperatuur van die dag verlaag. Dus as ons iets koeler as kaal rots sien, sou ons aflei dat dit waarskynlik 'n teken van 'n atmosfeer is, 'het Daniel Koll van die Massachusetts Institute of Technology (MIT), die hoofskrywer van twee van die artikels, verduidelik.

Webb is ideaal vir die maak van hierdie metings omdat dit 'n veel groter spieël het as ander teleskope, soos NASA se Hubble- of Spitzer-ruimteteleskope, wat dit moontlik maak om meer lig te versamel, en dit kan die toepaslike infrarooi golflengtes rig.

Die span se berekeninge toon dat Webb die hittehandtekening van 'n planeet se atmosfeer in een tot twee sekondêre verduisterings moet kan opspoor - net 'n paar uur waarnemingstyd. Daarenteen sal die opsporing van 'n atmosfeer deur middel van spektroskopiese waarnemings gewoonlik agt of meer deurgange vir dieselfde planete benodig.

Transmissiespektroskopie, wat sterlig bestudeer wat deur die planeet se atmosfeer gefiltreer word, ly ook aan steuring as gevolg van wolke of waas, wat die molekulêre handtekeninge van die atmosfeer kan masker. In daardie geval sou die spektrale plot in plaas daarvan om uitgesproke absorberingslyne as gevolg van molekules te toon, in wese plat wees.

'In transmissiespektroskopie, as u 'n plat lyn kry, vertel dit u niks. Die plat lyn kan beteken dat die heelal vol dooie planete is wat nie 'n atmosfeer het nie, of dat die heelal vol planete is met 'n hele reeks uiteenlopende, interessante atmosfeer, maar almal lyk dieselfde vir ons omdat hulle ' weer bewolk, ”het Eliza Kempton van die Universiteit van Maryland, 'n medeskrywer van drie van die artikels, gesê.

"Exoplanet-atmosfeer sonder wolke en waas is soos eenhorings - ons het dit nog net nie gesien nie, en dit bestaan ​​miskien glad nie," het sy bygevoeg.

Die span het benadruk dat 'n koeler as verwagte dagtemperatuur 'n belangrike leidraad sou wees, maar dit sou nie absoluut bevestig dat die atmosfeer bestaan ​​nie. Enige oorblywende twyfel oor die aanwesigheid van 'n atmosfeer kan uitgesluit word deur opvolgstudies met behulp van ander metodes soos transmissiespektroskopie.

Die ware krag van die nuwe tegniek sal wees om te bepaal watter deel van die rotsagtige eksoplanete waarskynlik 'n atmosfeer het. Ongeveer 'n dosyn eksoplanete wat die beste kandidate vir hierdie metode is, is gedurende die afgelope jaar opgespoor. Daar sal waarskynlik meer gevind word wanneer Webb in werking is.

"Die Transiting Exoplanet Survey Satellite, oftewel TESS, vind hope van hierdie planete," het Kempton gesê.

Die sekondêre verduisteringsmetode het een belangrike beperking: dit werk die beste op planete wat te warm is om in die bewoonbare sone geleë te wees. Om te bepaal of hierdie warm planete atmosfeer gasheer al dan nie, hou egter belangrike implikasies in vir bewoonbare sone-planete.

"As warm planete 'n atmosfeer kan vashou, moet koelers dit ook minstens kan doen," het Koll gesê.

Die James Webb-ruimteteleskoop sal die wêreld se voorste sterrewagsterrein wees wanneer dit in 2021 van stapel gestuur word. Webb sal raaisels in ons sonnestelsel oplos, verder kyk na verre wêrelde rondom ander sterre en die geheimsinnige strukture en oorsprong van ons heelal en ons plek daarin. Webb is 'n internasionale projek onder leiding van NASA met sy vennote, ESA (European Space Agency) en die Canadian Space Agency.


Kan die lewe 'n ster se dood oorleef? Die Webb-teleskoop kan die antwoord bekend maak

'N Planeet wat om 'n klein ster wentel, produseer sterk atmosferiese seine wanneer dit vooraan gaan, of' gas ', sy gasheerster, soos hierbo afgebeeld. Wit dwerge bied sterrekundiges 'n seldsame geleentheid om rotsagtige planete te kenmerk. Krediet: Carl Sagan Instituut

As sterre soos ons son sterf, is dit net 'n ontblote kern - 'n wit dwerg. Volgens navorsers van die Cornell Universiteit is 'n planeet wat om 'n wit dwerg wentel 'n belowende geleentheid om te bepaal of die lewe die ster van sy ster kan oorleef.

In 'n studie gepubliseer in die Astrofisiese joernaalbriewe, wys hulle hoe NASA se komende James Webb-ruimteteleskoop handtekeninge van die lewe op aardeagtige planete kon vind wat om wit dwerge wentel.

'N Planeet wat om 'n klein ster wentel, produseer sterk atmosferiese seine as dit vooraan beweeg, of as sy gasheerster' deurgaan '. Wit dwerge stoot dit tot die uiterste: hulle is 100 keer kleiner as ons son, amper so klein soos die aarde, wat astronome 'n seldsame geleentheid bied om rotsagtige planete te kenmerk.

"As daar rotsagtige planete rondom wit dwerge bestaan, kan ons die volgende paar jaar tekens van lewens op hulle sien," het die ooreenstemmende skrywer Lisa Kaltenegger, medeprofessor in sterrekunde aan die College of Arts and Sciences en direkteur van die Carl Sagan Instituut, gesê.

Die mede-hoofskrywer Ryan MacDonald, 'n navorsingsgenoot by die instituut, het gesê dat die James Webb-ruimteteleskoop, wat in Oktober 2021 van stapel gestuur is, uniek geplaas is om handtekeninge van die lewe op rotsagtige eksoplanete te vind.

"By die waarneming van aardagtige planete wat om wit dwerge wentel, kan die James Webb-ruimteteleskoop binne enkele ure water en koolstofdioksied opspoor," het MacDonald gesê. "Twee dae van die waarneming van tyd met hierdie kragtige teleskoop sou die ontdekking van biosignatuurgasse, soos osoon en metaan, moontlik maak."

Die ontdekking van die eerste reuse-planeet wat deur 'n wit dwerg wentel (WD 1856 + 534b), wat in 'n aparte artikel aangekondig is - gelei deur mede-outeur Andrew Vanderburg, assistent-professor aan die Universiteit van Wisconsin, Madison - bewys die bestaan ​​van planete rondom wit dwerge. Kaltenegger is ook medeskrywer van hierdie artikel.

Hierdie planeet is 'n gasreus en kan dus nie lewe onderhou nie. Maar die bestaan ​​daarvan dui daarop dat kleiner rotsagtige planete, wat lewe kan onderhou, ook in die bewoonbare sones van wit dwerge kan bestaan.

"Ons weet nou dat reuse-planete rondom wit dwerge kan bestaan, en bewyse strek oor 100 jaar wat toon dat rotsagtige materiaal besoedel lig van wit dwerge. Daar is beslis klein gesteentes in wit dwergstelsels," het MacDonald gesê. 'Dit is 'n logiese sprong om jou voor te stel dat 'n rotsagtige planeet soos die aarde 'n wit dwerg wentel.'

Die navorsers het die nuutste ontledingstegnieke gekombineer wat gereeld gebruik word om gasse in reuse-eksoplanetatmosfeer op te spoor met die Hubble-ruimteteleskoop met modelatmosfere van wit dwergplanete uit vorige Cornell-navorsing.

NASA se Transiting Exoplanet Survey Satellite is nou op soek na sulke rotsagtige planete rondom wit dwerge. As en wanneer een van hierdie wêrelde gevind word, het Kaltenegger en haar span die modelle en gereedskap ontwikkel om tekens van lewe in die atmosfeer van die planeet te identifiseer. Die Webb-teleskoop kan binnekort met hierdie soektog begin.

Die implikasies van die vind van handtekeninge van lewe op 'n planeet wat om 'n wit dwerg wentel, is diep, het Kaltenegger gesê. Die meeste sterre, insluitend ons son, sal eendag as wit dwerge beland.

"Sê nou die dood van die ster is nie die einde vir die lewe nie?" sy het gese. "Kan die lewe voortgaan, selfs as ons son eers gesterf het? Tekens van lewe op planete wat om wit dwerge wentel, wys nie net die ongelooflike hardnekkigheid van die lewe nie, maar miskien ook 'n kykie in ons toekoms."


NASA se Webb-teleskoop om jong eksoplanete aan die rand te bestudeer

Links: Dit is 'n beeld van die ster HR 8799 wat deur Hubble's Near Infrared Camera and Multi-Object Spectrometer (NICMOS) in 1998 geneem is. 'N Masker in die kamera (coronagraph) blokkeer die meeste lig van die ster. Sterrekundiges het ook sagteware gebruik om sterrelig digitaal af te trek. Nietemin, verspreide lig van HR 8799 domineer die beeld, en verdoesel vier dowwe planete wat later uit grondwaarnemings ontdek is. Regs: 'n Herontleding van NICMOS-data in 2011 het drie van die eksoplanete ontdek, wat nie in die 1998-beelde gesien is nie. Webb sal die planete se atmosfeer ondersoek op infrarooi golflengtes wat sterrekundiges selde gebruik het om verre wêrelde te beeld. Krediet: NASA, ESA en R. Soummer (STScI)

Voordat planete rondom ander sterre in die negentigerjare vir die eerste keer ontdek is, het hierdie verre eksotiese wêrelde slegs in die verbeelding van wetenskapfiksieskrywers geleef.

Maar selfs hul kreatiewe denke kon nie die verskeidenheid wêrelde wat sterrekundiges ontdek het, bedink nie. Baie van hierdie wêrelde, genaamd eksoplanete, verskil baie van die planetfamilie van ons sonnestelsel. Dit wissel van ster-omhelsende "warm Jupiters" tot groot rotsagtige planete wat "super Aarde" genoem word. Ons heelal is blykbaar vreemder as fiksie.

Om hierdie verre wêrelde te sien, is nie maklik nie, want hulle verdwaal in die glans van hul gasheersterre. Om hulle te probeer opspoor, is soos om 'n vuurvlieg langs die briljante baken van 'n vuurtoring te sien sweef.

Daarom het sterrekundiges die meeste van die meer as 4 000 eksoplanete wat tot dusver gevind is, geïdentifiseer met behulp van indirekte tegnieke, soos deur 'n ster se ligte wankeling of die onverwagte verdofding daarvan as 'n planeet voor hom verbygaan, wat die sterlig blokkeer.

Hierdie tegnieke werk egter die beste vir planete wat naby hul sterre wentel, waar sterrekundiges veranderinge gedurende weke of selfs dae kan opspoor as die planeet sy renbaan voltooi. Maar om slegs planete met sterrekyk te vind, bied sterrekundiges nie 'n omvattende beeld van al die moontlike wêrelde in sterstelsels nie.

Hierdie skema toon die posisies van die vier eksoplanete wat ver weg van die nabygeleë ster HR 8799 wentel. Die bane lyk langwerpig as gevolg van 'n effense kanteling van die baanvlak in verhouding tot ons siglyn. Die grootte van die HR 8799 planetêre stelsel is vergelykbaar met ons sonnestelsel, soos aangedui deur die baan van Neptunus, volgens skaal. Krediet: NASA, ESA en R. Soummer (STScI)

'N Ander tegniek wat navorsers gebruik in die jag op eksoplanete, of planete wat om ander sterre wentel, is een wat fokus op planete wat verder weg is van 'n ster se verblindende glans. Wetenskaplikes het jong eksoplanete ontdek wat so warm is dat hulle in infrarooi lig gloei met behulp van gespesialiseerde beeldtegnieke wat die glans van die ster blokkeer. Op hierdie manier kan sommige eksoplanete direk gesien en bestudeer word.

NASA se komende James Webb-ruimteteleskoop sal sterrekundiges help om verder in hierdie gewaagde nuwe grens te ondersoek. Webb, soos sommige teleskope op die grond, is toegerus met spesiale optiese stelsels genaamd coronagraphs, wat maskers gebruik om soveel moontlik sterlig te blokkeer om dowwe eksoplanete te bestudeer en nuwe wêrelde te ontbloot.

Twee teikens vroeg in die missie van Webb is die planetêre stelsels 51 Eridani en HR 8799. Van die enkele dosyn planete wat direk afgebeeld is, beplan sterrekundiges om Webb te gebruik om die stelsels wat die naaste aan die aarde is, met die grootste skeiding van hul planete te ontleed. sterre. Dit beteken dat hulle ver genoeg van 'n ster se glans af lyk om direk waargeneem te word. Die HR 8799-stelsel lê 133 ligjaar en 51 Eridani 96 ligjaar van die aarde af.

Webb se planetêre teikens

Twee waarnemingsprogramme vroeg in die missie van Webb kombineer die spektroskopiese vermoëns van die Near Infrared Spectrograph (NIRSpec) en die beelding van die Near Infrared Camera (NIRCam) en Mid-Infrared Instrument (MIRI) om die vier reuse planete in die HR 8799-stelsel te bestudeer. In 'n derde program sal navorsers NIRCam gebruik om die reuse-planeet in 51 Eridani te ontleed.

Hierdie ontdekkingsbeeld van 'n Jupiter-grootte buite-solêre planeet wat om die nabygeleë ster 51 Eridani wentel, is in 2014 in die nabye infrarooi lig geneem deur die Gemini Planet Imager. Die helder sentrale ster is versteek agter 'n masker in die middel van die beeld om die eksoplanet op te spoor, wat 1 miljoen keer flouer is as 51 Eridani. Die eksoplanet is aan die buitewyke van die planetêre stelsel 11 miljard myl van sy ster af. Webb sal die planeet se atmosfeer ondersoek op infrarooi golflengtes wat sterrekundiges selde gebruik het om verre wêrelde te beeld. Krediet: International Gemini Observatory / NOIRLab / NSF / AURA, J. Rameau (Universiteit van Montreal), en C. Marois (National Research Council of Canada Herzberg

Die vier reuse-planete in die HR 8799-stelsel is elk ongeveer 10 Jupiter-massas. Hulle wentel meer as 14 miljard myl van 'n ster wat effens massiewer is as die son. Die reuse-planeet in Eridani 51 is twee keer die massa van Jupiter en wentel ongeveer 11 miljard myl van 'n sonagtige ster af. Beide planetêre stelsels het wentelbane gerig op die aarde. Hierdie oriëntasie bied sterrekundiges 'n unieke geleentheid om 'n voëlvlug bo-op die stelsels te kry, soos om na die konsentrieke ringe op 'n boogskiet te kyk.

Baie eksoplanete wat in die buitenste wentelbane van hul sterre voorkom, verskil baie van ons sonnestelselplanete. Die meeste eksoplanete wat in hierdie buitenste streek ontdek is, insluitend dié in HR 8799, is tussen vyf en tien Jupiter-massas, wat hulle die massiefste planete tot nog toe gevind het.

Hierdie buite-exoplanete is relatief jonk, van tienmiljoene tot honderdmiljoene jare oud - baie jonger as ons sonnestelsel se 4,5 miljard jaar. Hulle gloei dus nog steeds van hitte van hul vorming. Die beelde van hierdie eksoplanete is in wese baba-prente, wat planete in hul jeug onthul.

Webb sal die middel-infrarooi ondersoek, wat sterrekundiges nog selde voorheen gebruik het om verre wêrelde te beeld. Hierdie infrarooi "venster" is moeilik waarneembaar vanaf die grond vanweë termiese emissie van en absorpsie in die aarde se atmosfeer.

"Die sterk punt van Webb is die ongeremde lig wat deur die ruimte in die middel-infrarooi bereik kom," het Klaus Hodapp van die Universiteit van Hawaii in Hilo, hoofondersoeker van die NIRSpec-waarnemings van die HR 8799-stelsel, gesê. "Die aarde se atmosfeer is redelik moeilik om deur te werk. Die belangrikste absorpsiemolekules in ons eie atmosfeer verhinder ons om interessante eienskappe in planete te sien."

Die middel-infrarooi "is die streek waar Webb regtig 'n belangrike bydrae sal lewer tot die begrip van die spesifieke molekules, wat is die eienskappe van die atmosfeer wat ons hoop om te vind, wat ons nie net kry van die korter, naby-infrarooi golflengtes, ”het Charles Beichman van die NASA se Jet Propulsion Laboratory in Pasadena, Kalifornië, hoofondersoeker van die NIRCam- en MIRI-waarnemings van die HR 8799-stelsel gesê. "Ons sal voortbou op wat die grondwaarnemings gedoen het, maar die doel is om dit uit te brei op 'n manier wat sonder Webb onmoontlik sou wees."

Een van die navorsers se hoofdoelstellings in beide stelsels is om Webb te gebruik om te bepaal hoe die eksoplanete gevorm het. Is dit geskep deur 'n opeenhoping van materiaal in die skyf wat die ster omring, verryk in swaar elemente soos koolstof, net soos Jupiter waarskynlik gedoen het? Of het hulle gevorm deur die ineenstorting van 'n waterstofwolk, soos 'n ster, en kleiner geword onder die onverbiddelike trek van swaartekrag?

Atmosferiese grimering kan leidrade gee oor die geboorte van 'n planeet. 'Een van die dinge wat ons graag wil verstaan, is die verhouding tussen die elemente wat in die vorming van hierdie planete gegaan het,' het Beichman gesê. "In die besonder vertel koolstof versus suurstof baie oor waar die gas vandaan kom wat die planeet gevorm het. Kom dit van 'n skyf wat baie van die swaarder elemente versamel het, of kom dit uit die interstellêre medium? Dit is dus wat ons noem die koolstof-tot-suurstof-verhouding wat 'n aanduiding is van vormingsmeganismes. "

Om hierdie vrae te beantwoord, sal die navorsers Webb gebruik om dieper in die atmosfeer van die eksoplanete te ondersoek. NIRCam meet byvoorbeeld die atmosferiese vingerafdrukke van elemente soos metaan. Daar word ook gekyk na wolkeienskappe en die temperature van hierdie planete. "Ons het reeds baie inligting op hierdie naby-infrarooi golflengtes vanaf grondgebaseerde fasiliteite," het Marshall Perrin van die Space Telescope Science Institute in Baltimore, Maryland, hoofondersoeker van die NIRCam-waarnemings van 51 Eridani b. "Maar die data van Webb sal baie meer presies en sensitiewer wees. Ons sal 'n meer volledige stel golflengtes hê, insluitend die invul van leemtes waar u die golflengtes nie van die grond af kan kry nie."

Die sterrekundiges sal ook Webb en sy uitstekende sensitiwiteit gebruik om te soek na minder massiewe planete ver van hul ster. "Uit waarnemings op grond weet ons dat hierdie massiewe planete relatief skaars is," het Perrin gesê. "Maar ons weet ook dat planete met 'n laer massa vir die binneste dele van stelsels dramaties meer algemeen voorkom as planete met 'n groter massa. Die vraag is dus: geld dit ook vir hierdie verdere skeidings?" Beichman het bygevoeg: "Webb se werking in die koue omgewing van die ruimte laat 'n soeke na flouer, kleiner planete toe wat onmoontlik is om van die grond af op te spoor."

'N Ander doel is om te verstaan ​​hoe die magdom planetêre stelsels tot dusver ontdek is.

"Ek dink wat ons vind is dat daar 'n groot verskeidenheid sonkragstelsels is," het Perrin gesê. "U het stelsels waar u hierdie warm Jupiter-planete in baie noue wentelbane het. U het stelsels waar u nie het nie. U het stelsels waar u 'n 10-Jupiter-massa planeet het en een waarin u niks meer massief het as verskeie Aarde nie. Uiteindelik wil ons verstaan ​​hoe die diversiteit van die vorming van planetêre stelsels afhang van die omgewing van die ster, die massa van die ster, allerhande ander dinge en uiteindelik hoop ons om ons eie sonnestelsel in hierdie bevolkingsvlakstudies te plaas. konteks. "

Die NIRSpec-spektroskopiese waarnemings van HR 8799 en die NIRCam-waarnemings van 51 Eridani maak deel uit van die waarborge-programme vir waarborge wat kort na die bekendstelling van Webb later vanjaar gedoen sal word. Die NIRCam- en MIRI-waarnemings van HR 8799 is 'n samewerking van twee instrumentspanne en is ook deel van die waarborgprogram vir gewaarborgde tyd.


Navorsingskassietitel

Voordat planete rondom ander sterre in die negentigerjare vir die eerste keer ontdek is, het hierdie verre eksotiese wêrelde slegs in die verbeelding van wetenskapfiksieskrywers geleef.

Maar selfs hul kreatiewe denke kon nie die verskeidenheid wêrelde wat sterrekundiges ontdek het, bedink nie. Baie van hierdie wêrelde, genaamd eksoplanete, verskil hemelsbreed van ons sonnestelsel se familie van planete. Hulle wissel van ster-omhelsende 'warm Jupiters' tot groot rotsagtige planete wat 'super aarde' genoem word. Ons heelal is blykbaar vreemder as fiksie.

Om hierdie verre wêrelde te sien is nie maklik nie, want hulle verdwaal in die glans van hul gasheersterre. Om hulle te probeer opspoor, is soos om 'n vuurvlieg langs die briljante baken van 'n vuurtoring te sien sweef.

Daarom het sterrekundiges die meeste van die meer as 4 000 eksoplanete wat tot dusver gevind is, geïdentifiseer met behulp van indirekte tegnieke, soos deur 'n ster se ligte wankeling of die onverwagte verdofding daarvan as 'n planeet voor hom verbygaan, en sommige van die sterlig blokkeer.

Hierdie tegnieke werk egter die beste vir planete wat naby hul sterre wentel, waar sterrekundiges veranderinge gedurende weke of selfs dae kan opspoor as die planeet sy renbaan voltooi. Maar die vind van slegs sterrekykende planete bied astronome nie 'n omvattende beeld van al die moontlike wêrelde in sterstelsels nie.

'N Ander tegniek wat navorsers gebruik in die jag op eksoplanete, dit is planete wat om ander sterre wentel, is een wat fokus op planete wat verder weg is van 'n ster se verblindende glans. Wetenskaplikes, wat gespesialiseerde beeldtegnieke gebruik wat die glans van die ster blokkeer, het jong eksoplanete ontdek wat so warm is dat hulle in infrarooi lig gloei. Op hierdie manier kan sommige eksoplanete direk gesien en bestudeer word.

NASA se komende James Webb-ruimteteleskoop sal sterrekundiges help om verder in hierdie gewaagde nuwe grens te ondersoek. Webb, soos sommige teleskope op die grond, is toegerus met spesiale optiese stelsels genaamd coronagraphs, wat maskers gebruik om soveel moontlik sterlig te blokkeer om dowwe eksoplanete te bestudeer en nuwe wêrelde te ontbloot.

Twee teikens vroeg in die missie van Webb is die planetêre stelsels 51 Eridani en HR 8799. Van die enkele dosyn planete wat direk afgebeeld is, beplan sterrekundiges om Webb te gebruik om die stelsels wat die naaste aan die aarde is, met die grootste skeiding van hul planete te ontleed. sterre. Dit beteken dat hulle ver genoeg van 'n ster se glans lyk om direk waargeneem te word. Die HR 8799-stelsel lê 133 ligjaar en 51 Eridani 96 ligjaar van die aarde af.

Webb se planetêre teikens

Twee waarnemingsprogramme vroeg in die missie van Webb kombineer die spektroskopiese vermoëns van die Near Infrared Spectrograph (NIRSpec) en die beelding van die Near Infrared Camera (NIRCam) en Mid-Infrared Instrument (MIRI) om die vier reuse planete in die HR 8799-stelsel te bestudeer. In 'n derde program sal navorsers NIRCam gebruik om die reuse-planeet in 51 Eridani te ontleed.

Die vier reuse-planete in die HR 8799-stelsel is elk ongeveer 10 Jupiter-massas. Hulle wentel meer as 14 miljard kilometer van 'n ster wat effens massiewer is as die Son. Die reuse-planeet in 51 Eridani is twee keer die massa van Jupiter en wentel ongeveer 11 miljard myl van 'n sonagtige ster af. Beide planetêre stelsels het wentelbane gerig op die aarde. Hierdie oriëntasie bied sterrekundiges 'n unieke geleentheid om 'n voëlvlug bo-op die stelsels te kry, soos om na die konsentrieke ringe op 'n boogskiet te kyk.

Baie eksoplanete wat in die buitenste wentelbane van hul sterre voorkom, verskil baie van ons sonnestelselplanete. Die meeste eksoplanete wat in hierdie buitenste streek ontdek is, insluitend dié in HR 8799, is tussen 5 en 10 Jupiter-massas, wat hulle die massiefste planete tot nog toe gevind het.

These outer exoplanets are relatively young, from tens of millions to hundreds of millions of years old—much younger than our solar system’s 4.5 billion years. So they’re still glowing with heat from their formation. The images of these exoplanets are essentially baby pictures, revealing planets in their youth.

Webb will probe into the mid-infrared, a wavelength range astronomers have rarely used before to image distant worlds. This infrared “window” is difficult to observe from the ground because of thermal emission from—and absorption in—Earth’s atmosphere.

“Webb’s strong point is the uninhibited light coming through space in the mid-infrared range,” said Klaus Hodapp of the University of Hawaii in Hilo, lead investigator of the NIRSpec observations of the HR 8799 system. “Earth’s atmosphere is pretty difficult to work through. The major absorption molecules in our own atmosphere prevent us from seeing interesting features in planets.”

The mid-infrared “is the region where Webb really will make seminal contributions to understanding what are the particular molecules, what are the properties of the atmosphere that we hope to find which we don’t really get just from the shorter, near-infrared wavelengths,” said Charles Beichman of NASA’s Jet Propulsion Laboratory in Pasadena, California, lead investigator of the NIRCam and MIRI observations of the HR 8799 system. “We’ll build on what the ground-based observatories have done, but the goal is to expand on that in a way that would be impossible without Webb.”

How Do Planets Form?

One of the researchers’ main goals in both systems is to use Webb to help determine how the exoplanets formed. Were they created through a buildup of material in the disk surrounding the star, enriched in heavy elements such as carbon, just as Jupiter probably did? Or, did they form from the collapse of a hydrogen cloud, like a star, and become smaller under the relentless pull of gravity?

Atmospheric makeup can provide clues to a planet’s birth. “One of the things we’d like to understand is the ratio of the elements that have gone into the formation of these planets,” Beichman said. “In particular, carbon versus oxygen tells you quite a lot about where the gas that formed the planet comes from. Did it come from a disk that accreted a lot of the heavier elements or did it come from the interstellar medium? So it’s what we call the carbon-to-oxygen ratio that is quite indicative of formation mechanisms.”

To answer these questions, the researchers will use Webb to probe deeper into the exoplanets’ atmospheres. NIRCam, for example, will measure the atmospheric fingerprints of elements like methane. It also will look at cloud features and the temperatures of these planets. “We already have a lot of information at these near-infrared wavelengths from ground-based facilities,” said Marshall Perrin of the Space Telescope Science Institute in Baltimore, Maryland, lead investigator of NIRCam observations of 51 Eridani b. “But the data from Webb will be much more precise, much more sensitive. We’ll have a more complete set of wavelengths, including filling in gaps where you can’t get those wavelengths from the ground.”

The astronomers will also use Webb and its superb sensitivity to hunt for less-massive planets far from their star. “From ground-based observations, we know that these massive planets are relatively rare,” Perrin said. “But we also know that for the inner parts of systems, lower-mass planets are dramatically more common than larger-mass planets. So the question is, does it also hold true for these further separations out?” Beichman added, “Webb’s operation in the cold environment of space allows a search for fainter, smaller planets, impossible to detect from the ground.”

Another goal is understanding how the myriad planetary systems discovered so far were created.

“I think what we are finding is that there is a huge diversity in solar systems,” Perrin said. “You have systems where you have these hot Jupiter planets in very close orbits. You have systems where you don’t. You have systems where you have a 10-Jupiter-mass planet and ones in which you have nothing more massive than several Earths. We ultimately want to understand how the diversity of planetary system formation depends on the environment of the star, the mass of the star, all sorts of other things and eventually through these population-level studies, we hope to place our own solar system in context.”

The NIRSpec spectroscopic observations of HR 8799 and the NIRCam observations of 51 Eridani are part of the Guaranteed Time Observations programs that will be conducted shortly after Webb’s launch later this year. The NIRCam and MIRI observations of HR 8799 is a collaboration of two instrument teams and is also part of the Guaranteed Time Observations program.

The James Webb Space Telescope will be the world's premier space science observatory when it launches in 2021. Webb will solve mysteries in our solar system, look beyond to distant worlds around other stars, and probe the mysterious structures and origins of our universe and our place in it. Webb is an international program led by NASA with its partners, ESA (European Space Agency) and the Canadian Space Agency.

Donna Weaver
Space Telescope Science Institute, Baltimore, Maryland

Christine Pulliam
Space Telescope Science Institute, Baltimore, Maryland


James Webb Will Look for Signs of Life on Planets Orbiting Dead Stars

Can the galaxy’s dead stars help us in our search for life? A group of researchers from Cornell University thinks so. They say that watching exoplanets transit in front of white dwarfs can tell us a lot about those planets.

It might even reveal signs of life.

A new study presents this idea in The Astrophysical Journal Letters. The research is titled “The White Dwarf Opportunity: Robust Detections of Molecules in Earth-like Exoplanet Atmospheres with the James Webb Space Telescope.” The lead and corresponding author is Lisa Kaltenegger, associate professor of astronomy in the College of Arts and Sciences at Cornell. Kaltenegger is also the director of the Carl Sagan Institute.

“If rocky planets exist around white dwarfs, we could spot signs of life on them in the next few years,” said Kaltenegger in a press release.

One of the goals of the James Webb Space Telescope (JWST) is to characterize exoplanet atmospheres using spectroscopy. The JWST has the power to do that with very distant planets. While other facilities can do spectroscopy, the JWST has the added benefit of doing it in the infrared. In infrared light, molecules in a planet’s atmosphere have the largest number of features in their spectra, making them easier to identify.

“What if the death of the star is not the end for life?”

Lisa Kaltenegger, Lead Author, Professor, Cornell University

But this study takes the JWST and its atmosphere-observing powers in a different direction. While exoplanet research and the search for life normally focuses on planets transiting small M-dwarfs, the authors say there might be a better way. They point out that finding white dwarfs with planets transiting in front of them is a way to advance the search for life. That’s partly because detecting potential biosignatures would be easier.

The James Webb Space Telescope, with its iconic segmented mirror, sits inside a cleanroom at NASA’s Johnson Space Center in Houston. This newest study is just one more reson we can’t wait for this telescope to get to work. Credit: NASA/JSC

Detecting biosignatures around M-dwarfs is challenging. The powerful light output from the large stars makes it harder to see what’s going on in their vicinity. And M-dwars are known for the high level of sunspot and flaring activity. All that activity could impair spectroscopic searches for biomarkers. In their paper, the authors explain that “Earth-like planets around cool small M dwarfs, such as TRAPPIST-1, are promising targets for characterization with the upcoming Extremely Large Telescopes (ELTs) and JWST. However, there remain outstanding challenges in interpreting transmission spectra of M-dwarf terrestrial planets, notably contamination from unocculted starspots.”

But white dwarfs are different. They’ve run out of nuclear fuel and have shrank down to only a remnant core. They still provide enough light for spectroscopic investigation of their exoplanet atmospheres, but they don’t overwhelm the signal with their own luminosity. And since they’re no longer actively burning nuclear fuel, solitary white dwarfs don’t flare, so they don’t impair spectroscopic results. (They can flare if they’re in a binary relationship).

The authors say that by focusing on white dwarfs, the JWST should be able to identify water and carbon dioxide—both substances correlated with living processes—in as little as a couple of hours.

“When observing Earth-like planets orbiting white dwarfs, the James Webb Space Telescope can detect water and carbon dioxide within a matter of hours,” MacDonald said. “Two days of observing time with this powerful telescope would allow the discovery of biosignature gases, such as ozone and methane.”

This figure from the study shows simulated JWST detections of biomarkers in the atmosphere of an Earth-like planet orbiting a white dwarf. Image Credit: Kaltenegger et al, 2020.

A few discoveries led to this potential new method of searching for signs of life.

White dwarfs go through a lot of changes as they leave the main sequence. Their progenitor star sheds its outer layers in a series of violent convulsions that should spell doom for any planets orbiting them. In its red giant phase, the star expands to envelop any planetary bodies that are too close. This will happen to our own Sun in several billion years. The Sun will envelop and destroy Mercury, Venus, maybe even Earth.

But sometimes planets might survive the process.

After several billions years, yellow suns (like ours) become Red Giants, expanding to several hundred times their normal size. Then they’ll eventually become white dwarfs. Credit: Wendy Kenigsburg

The authors explain in their paper that “The origin and survival of close-in planets orbiting WDs have seen active theoretical study. Once a main-sequence star evolves into a WD, stable planetary systems can undergo violent dynamical instabilities, exciting planets into high-eccentricity, low-pericenter orbits. These orbits can rapidly circularize due to tidal dissipation, leading in some circumstances to the survival of planets in close-in orbits.”

When astronomers discovered planets orbiting a white dwarf, things went from theoretical to practical a very significant development.

At first, astronomers studying white dwarfs saw evidence of rocky debris near the dead stars. The debris was orbiting in debris disks, or even closer to the star, or right in the star’s atmosphere. Scientists interpreted that as evidence of planets destroyed as the star became a white dwarf.

Artist impression of a disk of material around a white dwarf star. Image credit: Gemini Observatory

In September 2019, astronomers discovered a giant planet candidate orbiting a white dwarf. This was evidence that large planets can survive their star’s transition to white dwarf. They may survive via migration. And around the same time, in November 2019, scientists discovered a planet that’s orbiting a red giant, having survived that star’s transition to its red giant phase.

Astronomers have found a white dwarf star which appears to be surrounded by a truncated disc of gas. The disc was probably created from a gas planet being torn apart by its gravity. Beeldkrediet: NASA

In December 2019, a team of astronomers discovered a Neptune-sized planet orbiting a white dwarf much smaller than itself. They couldn’t see the planet itself, just the atmosphere of the planet as the white dwarf stripped it away. The planet was likely doomed, but it proved that white dwarfs can still host exoplanets. And though this one was a gas giant, and unlikely to host any life, it shows that rocky planets may survive around white dwarfs, too.

That’s where this work comes in.

“We know now that giant planets can exist around white dwarfs, and evidence stretches back over 100 years showing rocky material polluting light from white dwarfs. There are certainly small rocks in white dwarf systems,” MacDonald said. “It’s a logical leap to imagine a rocky planet like the Earth orbiting a white dwarf.”

Artist’s rendition of a white dwarf from the surface of an orbiting exoplanet. Image Credit: Madden/Cornell University

NASA’s TESS spacecraft is the premiere planet-hunting spacecraft of the day. Part of its search involves hunting for rocky planets around white dwarfs. White dwarfs are small, and their planets should have short transition times, just like WD 1856+534, the giant planet candidate found in September 2019. That one took only about two minutes to transit, and planets with shorter transit times are more likely to be spotted.

Usually, an exoplanet is dwarfed by its star, and all that light blinds us to the sight of the planet. But with white dwarfs, that’s not the case. The authors explain in their paper that “Transiting planets orbiting smaller stars are generally easier to characterize, due to their increased planet-to-star size ratio.” The rapid repetition of transits makes it easier to identify biomarkers spectroscopically.

As the authors write in their paper, “Rocky planets in the WD habitable zone therefore represent a promising opportunity to characterize terrestrial planet atmospheres and explore the possibility of a second genesis on these worlds.”

If, or when, TESS finds rocky planets orbiting a white dwarf, Kaltenegger and her colleagues will be ready. They took established Hubble Space Telescope methods of identifying gases in exoplanet atmospheres and have combined them with modelled atmospheres of white dwarf planets from other research. So once the JWST is operational, the groundwork for understanding exoplanet atmospheres spectroscopically is already in place.

An artists’s illustration of TESS, the Transiting Exoplanet Survey Satellite. Beeldkrediet: NASA

What if we did find life on a planet orbiting a white dwarf? The implications are stunning. Since most stars in the Milky Way, including our own, will end their lives as white dwarfs, the proposition is astounding. In fact, astrophysicists think that over 97% of the stars in our galaxy will become white dwarfs. Could life have survived on planets that survived their stars’ transition? Or, even more exciting, could life have re-emerged?

“What if the death of the star is not the end for life?” she said. “Could life go on, even once our sun has died? Signs of life on planets orbiting white dwarfs would not only show the incredible tenacity of life, but perhaps also a glimpse into our future.”


CSI: Aliens--Astronomers Prep to Detect Cryptic Exoplanet Biosignals

Carl Sagan described Earth as viewed from space as a pale blue dot, and our first direct images of light-years distant planets will be just as minuscule. When new mega-telescopes capture their first pictures of exoplanets, we will at best see half pixels of grayish blur. Even so, investigators eager to learn whether any exoplanets harbor life might be able to find hints in those first fuzzy images. First, however, they will need to know what biosignatures would look like in data coming from worlds very different from our own.

Many teams are now focusing on finding answers. The latest entrant is Cornell&rsquos Institute for Pale Blue Dots, officially launching on May 9 (and also just renamed the Carl Sagan Institute). The institute has been working to create a database of "fingerprints" for life that could be discerned in the light reaching telescopes from exoplanets.

That is because much of the early information about distant planets will come in the form of an electromagnetic spectrum: the wavelengths a planet radiates, either directly or via light from its star shining through its atmosphere. This spectrum can reveal the chemicals in the exoplanet&rsquos atmosphere and, sometimes, on its surface. Earth, for example, would look green from all the photosynthesizing plants (plus blue from water, with a hint of pearly clouds) and would offer other signs of life as well. Our spectrum would reveal the presence of water vapor&mdasha strong hint that the planet is amenable to life&mdashas well as abundant oxygen and methane. That latter combination over time would indicate oxygen was being renewed somehow, because methane degrades oxygen and yet the oxygen does not disappear. Such a process would be an indication of life, which is one of the most likely sources of renewed oxygen in large quantities. Similar signatures on other planets&mdashindicative of oxygen, methane, water and maybe even the green of photosynthesizing plants&mdashwould suggest they were amenable to carbon-based life like that found on Earth.

Of course, an exoplanet's spectrum could be very different from our own, making signs of life harder to parse. If the atmosphere is full of hydrocarbons, like the surface of Saturn&rsquos largest moon Titan, it would be hard to make out anything closer to the surface through the haze. Similarly, dense cloud cover, like on Venus, would reflect light back and obscure the other gases below. Or vigorous geologic activity venting gas might obscure smaller amounts of other gases being created. And so researchers are simulating what a planet&rsquos spectrum would look like in such cases&mdashand many other scenarios, from a dust-covered dune world to one covered with water or circling a very dim star. &ldquoIn a way, it&rsquos a CSI for exoplanets,&rdquo Lisa Kaltenegger, an astronomer and head of the new institute, says about the burgeoning database of those simulations. Much like forensic investigators identify who committed a crime from signs like fingerprints and DNA, exoplanet researchers will be able to compare that database of spectra with real measurements from planets, working backward to see what kind of body generates that spectrum. Kaltenegger notes that she does not want to miss signs of life just because they occur on a planet bigger, smaller, hotter, colder, younger or older than Earth and the other planets in our solar system.

The most intricate atmospheric simulations available were built for Earth and incorporate details specific to its atmosphere and geography. Although they are good for weather forecasting and precise analysis researchers don&rsquot have enough details about other planets to build something so complicated for them. Instead, Kaltenegger&rsquos group is focusing on simpler, &ldquoone-dimensional&rdquo simulations that model the whole climate and atmosphere uniformly, as if you only had one glimpse of the whole thing. A one-dimensional model can incorporate and explore the effect of all the different types of gases, planetary structures, types of stars and life you could imagine, but treats a planet&rsquos atmosphere as one uniform mixture it is not tracking clouds moving over the surface but rather averaging all the water vapor in the air at once. And it is well suited to help astronomers understand the very first planetary images they will see, which will be a single point anyway.

As telescopes become more sophisticated, astronomers will gather more detailed information about an exoplanet&rsquos properties than can be gleaned from the best instruments we have now or are currently building. Telescopes that can image the planet directly, with reflected light from its star, will fill in missing details about rotation, geography and seasons. Such information can help to reveal what features life would need to survive on a given world. A tidally locked world, with one side always facing its sun, for instance, would have very different conditions than its averaged environment might suggest&mdashbitterly cold on one side and fiercely hot on the other&mdashand be hospitable to different types of organisms than those that might be found on a uniformly temperate planet.

And simulation, as it gets more detailed, can reveal the unexpected: When Dimitar Sasselov, an astronomer at Harvard&ndashSmithsonian Center for Astrophysics, helped model a planet covered entirely in water, he discovered a totally unknown form of &ldquowarm ice&rdquo at the bottom of that vast ocean where the pressure pushes the water at the ocean floor into a dense solid form, and waves might move continuously across the surface, never breaking. This scenario allows scientists to consider what features life would need to arise and persist under those conditions, even biology alien to anything we know now.

Simulation can also unmask signatures that seem to represent life but could be created by nonbiological processes. Victoria Meadows, principal investigator at the University of Washington's Virtual Planet Laboratory, says that trying to predict the signatures that might fool them has led to many of her group&rsquos discoveries. For instance, the lab recently released a paper on four separate ways oxygen could be generated without life being involved. Knowing those, they can work out measurements that telescopes will have to take to discount those alternate causes. They can also pinpoint which spectral fingerprints would be most telling of potential life.

These simulation tools are only the first step: to identify what form life might take and what signatures those forms might provide, astronomers are partnering across disciplines and taking unfamiliar excursions into the biology lab. For instance, Kaltenegger&rsquos group has studied the spectra of 137 microorganisms, including extremophiles that thrive in Earth's most inhospitable environs. This color catalogue provides the data that advanced telescopes would see if a planet's dominant organisms were suited for very different environments so we might recognize them from afar. Sasselov&rsquos Origins of Life Initiative brings people from all disciplines to run experiments exploring the ingredients needed to create life and the steps by which it forms. In essence, they are asking: If we looked at the early Earth through a telescope, how would we recognize the life on it? They are also pondering how&mdashand what&mdashcompletely different life-forms might arise. &ldquoThere&rsquos going to be a lot of things we haven&rsquot considered but we&rsquore trying to come up with as diverse and fascinating a world as we can,&rdquo Kaltenegger says, &ldquoto make the parameter space large, to not miss signatures if we can help it.&rdquo

The Kepler space telescope revealed just how common exoplanets are by spotting the slight dimming of starlight they cause when transiting, or passing in front, of their stars. TESS, a similar mission to look for planets closer to home, will identify options bright enough to examine in more detail. When future tools, such as the James Webb Space Telescope, coming in 2018, turn their sights to exoplanets, they&rsquoll have only a limited chance to gather the details of planetary atmospheres as their stars shine through them. Future telescopes will be able to see a dot of actual surface color. By then, however, exoplanet researchers plan to be ready. They are building a vast picture of what life can be, how it might manifest itself and how to verify that it is real&mdashto know just what to look for in that tiny smudge of color.

&ldquoWe&rsquore in a world in which familiar is not necessarily what we see out there,&rdquo Sasselov says. &ldquoThat&rsquos the big problem as well as the big opportunity.&rdquo


Astronomers will probe exoplanets with Webb telescope

This month marks the third anniversary of the discovery of a remarkable system of seven planets known as TRAPPIST-1. These rocky, Earth-size worlds orbit an ultra-cool star 39 light-years from Earth 1 light-year is approximately 5.88 trillion miles.

Three of the planets are in the “habitable zone,” meaning they are at the right orbital distance to be warm enough for liquid water to exist on their surfaces. NASA’s James Webb Space Telescope will observe those worlds after its launch in 2021, with the goal of making the first detailed, near-infrared study of the atmosphere of a habitable-zone planet.

Numerous Cornell astronomy faculty will contribute to the mission. Nikole Lewis, assistant professor of astronomy and the deputy director of the Carl Sagan Institute, is the principal investigator for one of the teams investigating the TRAPPIST-1 system.

“It’s a coordinated effort because no one team could do everything we wanted to do with the TRAPPIST-1 system,” Lewis said. “The level of cooperation has been really spectacular.”

Lewis’ team will observe one of the planets, TRAPPIST-1e, in an effort to not only detect an atmosphere, but also to determine its basic composition. They expect to be able to distinguish between an atmosphere dominated by water vapor and one composed mainly of nitrogen (like Earth) or carbon dioxide (like Mars and Venus).

TRAPPIST-1e is one of the known exoplanets having the most in common with Earth its density and the amount of radiation that it receives from its star make it a great candidate for habitability. Lewis will also lead 130 hours of guaranteed time observations focused on the detailed study of exoplanet atmospheres with Webb.

Ray Jayawardhana, the Harold Tanner Dean of Arts and Sciences and professor of astronomy, and Lisa Kaltenegger, associate professor of astronomy and director of the Carl Sagan Institute, are part of a team that will dedicate 200 hours of time on the Webb telescope to characterize exoplanets, including Trappist-1d (a hot, rocky, Venus-like planet) and Trappist-1f (a cooler, Earth-size planet).

“We look forward to ‘remote sensing’ a remarkable diversity of exoplanet atmospheres, ranging from temperate terrestrial worlds in the TRAPPIST-1 system to blazing gas giants orbiting very close to their stars,” Jayawardhana said. “The Webb telescope will give us unprecedented views, especially of the smaller planets that are tougher to probe.”

Added Kaltenegger: “The combination of the data from the three TRAPPIST planets will give us unprecedented insight into how rocky planets evolve at different distances from their host star. It is the best laboratory that we could have asked for, to get insights into how extrasolar rocky planets work.”

Jonathan Lunine, David C. Duncan Professor in the Physical Sciences and chair of astronomy, is the interdisciplinary scientist for astrobiology on the Webb mission and serves on the Science Working Group, which defines the mission’s science requirements and provides scientific oversight of the project. His hours on the telescope will be mostly used to look at “hot Jupiters” – gas giant planets that are very close to their stars – and Kuiper Belt objects.

James Lloyd, professor of astronomy, developed the Aperture Masking Interferometry mode of the telescope’s Near-Infrared Imager and Slitless Spectrograph (NIRISS) instrument, which will be used to image planetary systems and their environments.

The Webb telescope will be the world’s premier space science observatory, able to solve mysteries in our solar system, look beyond to distant worlds around other stars, and probe the enigmatic structures and origins of our universe. Webb is an international program led by NASA, with partners the European Space Agency and the Canadian Space Agency.


Of light and life

Scanning this light for atmospheric molecules could reveal all kinds of secrets about the planets in the TRAPPIST-1 system, including possibly the building blocks of life.

"By spreading out that light like a rainbow, we can look for signatures of molecules and atoms in the atmosphere, including oxygen, methane and water vapor, all potential signatures of life," says Burgasser. "JWST can also be used to measure the reflection of starlight off of the planets when they pass behind the star. This is called a 'secondary eclipse.' This would potentially allow us to study the surfaces of the planets."

Once assembled, the James Webb Space Telescope will span the size of a tennis court

While it will be a big player in exoplanet research in the coming decades, the JWST is just one of a number of tools scientists will use to search these worlds for signs of life. The Giant Magellan Telescope, for example, will feature an aperture 15 times that of JWST and will start scanning the night sky from Chile's Atacama Desert sometime in the mid-2020s. With these, plus other larger telescopes and yet-to-be developed technologies entering the fray, how much will we learn about the TRAPPIST-1 system without ever actually going there?

"Quite a lot," says Burgasser. "In addition to the atmosphere and surface measurements, we have some earlier measurements of mass, but with higher precision instruments and larger telescopes, we could improve those measurements and get a firm measure of the planets' average density, which in turn would tell us if they are mostly rocky, like Earth, or a mixture of rock and ice, like Jupiter's moon Ganymede. There is a chance one or more of these planets have moons, which may show up in more detailed transit measurements."

And as Burgasser explains, the things discovered in the TRAPPIST-1 system might be just as vital in answering key questions as the things that are not.

"We are also looking for evidence that the planets may be losing their atmospheres due to magnetic winds coming from the star, an important consideration to determine whether water is retained on their surfaces," he says. "And of course the big question is life itself, did it arise on any of these planets? Are they even hospitable to life? All of the measurements above are important ingredients to answering these truly big questions."

The video below (provided by the European Southern Observatory) offers a few early and interesting facts about these newly discovered worlds.