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TRAPPIST-1 Press Release FrequentlyAskedQuestionsforInformalLearningEnvironments Foradditionalinformation,besuretocheckouttheNASAExoplanetExplorationFAQand Glossary. • NASAExoplanetExplorationFAQ-https://exoplanets.nasa.gov/faq/ • NASAExoplanetExplorationGlossary-https://exoplanets.nasa.gov/glossary/ TRAPPIST-1FAQ 1. Whatmakesthisdiscoveryspecial? Therearemanyreasonswhythisdiscoveryistrulyspecial.ThediscoveryofsevenEarth-sized planetsinthesamestarsystemhasprofoundimplicationsforoursearchforhabitableworlds outsideofoursolarsystem.Ontopofthat,thisisthefirsttimethatpeoplehavediscovereda starsystemwithmorethanoneplanetinthehabitablezonethatwecanexaminewithtransit spectroscopy.Transitspectroscopyisthemeasurementofaplanet’satmospherewhileit transitsitshoststarviastudyinghowthelightfromthehoststarbehavesasitpassesthrough theplanet’satmosphere.Bybreakingupthislightintoitsconstituentcolorsviaaspectrograph, wecanlearnaboutthechemicalcompositionoftheplanet’satmosphere. Additionally,thereasonablylowactivitylevelofthecentralstarmeanstheyaremorelikelyto beabletosupportlife.Finally,thesystemisreallyclose,only39light-yearsaway.Thatmakesit easierforustolearnmorewithourcurrentobservatories–Spitzer,Hubble,Kepler,and ground-basedtelescopes–andpossiblylearntheanswerstomoreburningquestionswiththe soon-to-comeJamesWebbSpaceTelescope. 2. WhyisthisplanetarysystemcalledtheTRAPPISTsystem? TheTRAPPISTsystemisnamedaftertheTRAnsitingPlanetsandPlanetesImalsSmallTelescope (TRAPPIST)robotictelescopes.TherobotictelescopesarelocatedinChileandMorocco,but theyareledbyastrophysicistsinBelgium.Becausethesetelescopesdiscoveredthefirst exoplanetsinthesystemin2016,thesystemwasnamedTRAPPIST-1.Thenumber1refersto thefactthatthisisthefirstsystemnamedafterthesetelescopes.Theprogramname (TRAPPIST)isanodtothemonasticorderintheBelgiumregion,knownbymanyforbrewing Trappistbeers. 1 TRAPPIST-1 Press Release 3. HowdidwefigureoutthereweremoreplanetsintheTRAPPIST-1system? WeoriginallyfoundplanetsintheTRAPPIST-1systembylookingatvariationsinlightcoming fromthestar.Thelightgetsdimmerandformsawigglepatternwhenplanetstransit,orpass, betweenthestarandtheEarth.Thepatternchangesdependingonhowmanyplanetsthere are,howfasttheyorbit,andotherfactors.NASA’sSpitzerSpaceTelescopewasabletoobserve thesystemformultipletransitsatahigherprecisionthantheTRAPPISTtelescopecould.So whenthewigglepattern—whichwasactuallyatleastsevenplanetswigglingontopofeach other—isobservedlongenoughathigh-enoughprecision,wecandisentanglethesignatures oftheindividualplanets.OfcoursetherecouldbeevenMOREplanetshiddenbeyondour detectionlimit:theirorbitsmaybetoolong,theymaybetoosmalltobedetected,ortheymay beexactlyinresonancewithoneoftheexistingplanetswefound. 4. WhywasSpitzerlookingatasystemwealreadyknewabout? TheSpitzerSpaceTelescopewaslookingattheTRAPPIST-1systembecauseitcouldget*very* accuratemasses,densities,andotherpropertiesthatareimpossiblefromeventhemoststable ground-basedobservatory.TheEarth'satmospherelimitsourultimateabilitytodetectthese properties.Italsolimitsourabilitytodetectthegasesthatmightbepresentaroundan exoplanet(notably,water.)Furthermore,Spitzerisaninfraredtelescope,sotherearespecific propertiesitcandeterminethatcannotcurrentlybeobservedelsewhere,evenbyNASA’s HubbleSpaceTelescope. Onceweknewtherewereplanets,therewasalottobegainedbydoingadeeperstudywith Spitzertolearnmoreaboutthem.Thisdiscoverystartedwithaground-basedfacility- TRAPPIST–thatlookedatalargenumberofstars,searchingforexoplanets.Thenwepointed space-basedfacilitieslikeSpitzerandHubbleontheTRAPPISTsystembecausetheTRAPPIST telescopefoundsomethinginteresting.Lotsofastronomerscompeteforalimitedamountof timetostudyobjectswithspacetelescopes.Sospacetelescopesgenerallydonotstareatastar forlongperiodsoftimelookingforexoplanetsunlessanothertelescopehasproduceddata indicatingtheymightbethere.Wecan’tlookateverythingwithSpitzer/Hubble,butoncewe haveapromisingtarget,thecaseforusingSpitzerorHubbletoobserveasystembecomes stronger.SpitzerjusthappenedtofindadditionalplanetsintheTRAPPISTsystemwhileitwas observingtheknownexoplanetsoriginallyspottedbytheTRAPPISTtelescope. 2 TRAPPIST-1 Press Release GeneralExoplanetFAQ 1. Howareexoplanetsnamed? Exoplanetsarenamedaftertheirparentstar,andgivenlowercaselettersbasedonwhenthey arediscoveredandontheirdistancefromtheirhoststar.Forexample,TRAPPIST-1Aisthe TRAPPIST-1star.TRAPPIST-1bandTRAPPIST-1cwerethefirstplanetsdiscoveredaroundthis star,with1bbeingtheclosesttothestarand1cbeingthenextclosest.Thethirdplanet originallythoughttobepartofthesystemturnedouttoactuallybethreedifferentplanets. Sincethiswascaughtearly,thenewplanetswerenamed1d,1e,1f,1g,and1h,goingfrom closesttofarthest.IfwediscoveredaneighthplanetorbitingTRAPPIST-1Afiveyearsfromnow, itwouldbecalledTRAPPIST-1i,regardlessofitslocation. 2. Whatisanexoplanet? Thetermexoplanetoriginallycomesfromextra-solarplanet,whichjustmeansaplanetorbiting astarotherthanourSun.Otherstarsarereallyfaraway.Astar’sbrightnessmakesitincredibly difficulttodetectanearbyorbitingbody.Giventheseobservationaldifficulties,exoplanets werenotdetecteduntilquiterecently(theearly1990’s).Astronomersneededtocreateseveral ingenioustechniquestofindandstudythem.Nowtherearethousandsofconfirmed exoplanets,thousandsmorethatarecandidateexoplanetsawaitingconfirmationwithmore data,andfuturemissionsdevotedtofindingandcharacterizingthem. 3. HowmanyEarth-sizeplanetshavewefoundsofar? Atthetimeofthisdiscovery,therewereapproximately340confirmedterrestrialplanets known.TheseareplanetsthatarearoundthesamesizeastheEarth(source:NASA’sExoplanet Archive).Thisnumbercomprisesabout10percentofallconfirmedexoplanets.Theothertypes ofexoplanetsareicegiants(likeNeptuneandUranus),gasgiants(likeJupiterandSaturn),and super-Earths(planetsthatfallbetweenNeptune/UranusandEarthinsize,ofwhichthereare nocounterpartsinoursolarsystem). 3 TRAPPIST-1 Press Release 4. Whatisthehabitablezone? Habitablemeanssuitableforlife.TheoneconstantforlifeonEarthistheexistenceofliquid water.So,thesimplestanswertothisquestionisthehabitablezoneistheregionaroundastar whereliquidwatercanexist.Ifanexoplanetistooclose,itwillbetoohotandwaterwill evaporate.Ifanexoplanetistoofar,itwillbetoocoldandwaterwillfreeze.Giventhatstars comeinarangeofsizesandtemperatures,thehabitablezonewillchangedependingonthe typeofstararoundwhichanexoplanetorbits. Anothercommondefinitionforhabitablezoneiswheretheaveragetemperaturefallsin betweentheaverageonthesurfaceofVenusandMars,NOTaccountingforatmospheric effectslikeVenus'srunawaygreenhouse.Wedonotyetknowmuchabouttheatmospheresof mostofthediscoveredexoplanets,andhabitabilityisacomplicatedconceptbecausean atmospheregreatlyimpactswhetherornottheexoplanetistoohot,toocold,orjustrightfor liquidwatertoexist.Includingatmosphericeffectsaretrulycriticalforactuallyunderstanding whetherornotanexoplanetishabitableandwillbecriticalinfuturestudiesofhabitability. Ofcourse,beinginahabitablezonedoesnotguaranteehabitability(e.g.,theMoon).Beingout ofthehabitablezonedoesnotnecessarilymeantheplanetormoonisnothabitable(e.g., Europa,amoonofJupiterthatcouldhaveliquidwater).Butthehabitablezoneisapowerful indicatorofwhereliquidwatermightmosteasilybefound.Hence,theideaofahabitablezone isaguideforastronomerssearchingforplacesinouruniversewherelifemightexist. 5. HowmanyEarth-sizeplanetshavewefoundinahabitablezone? Atthetimeofthisdiscovery,thereweresixexoplanetslabeledas“potentialEarths,”basedon theirsizeandlocationwithintheirsystems’habitablezone.Thenewdiscoveriesbringthetotal uptonine. 6. Whydowelookforexoplanets? OneofNASA’sbiggoalsinthestudyoftheuniverseistoaddressthequestion,“Arewe Alone?,”bysearchingforlifeonplanetsaroundotherstars.Thisquestion,ponderedbyhumans forcenturies,isjustnowbeginningtobedirectlyaddressed,thankstonewtechnologiesin telescopesandnewstrategiesinsearchingforexoplanets.Beforewecandirectlyanswerthe primaryquestion,wefirsthavetofindtheexoplanetsandbegintocharacterizetheir properties.Forexample,aretheyEarth-sized,inthehabitablezone,andhabitableasdefined bythematerialintheiratmospheres?Thesearethequestionswearejustnowbeingableto answer. 4 TRAPPIST-1 Press Release 7. WhatdowemeanbyEarth-likeexoplanets? “Earth-like”iscommonlyusedtorefertoexoplanetsthatareaboutthesamesizeasEarthAND resideinthehabitablezone. Aswelearnmoreaboutexoplanets,weareabletousenewdatatoreducethenumberof exoplanetsthatmaytrulybeEarth-like.IntheTRAPPISTsystem,wehavegoodinformationon themassesandsizesoftheexoplanets.Thisinformationcanprovideameasurementofthe bulkdensitiesoftheexoplanets.Thebulkdensity(mass/volume)cantellusiftheexoplanetis composedofrock,metal,water,orgas. Ultimately,totrulytellifanexoplanetisEarth-like,weneedtoknowifitcansupportlifeaswe knowit.Todothat,weneedtotakedetailedspectraoftheiratmospherestodiscoverwhatthe atmospheresaremadeof.Ifwefindexoplanetatmosphereswithamountsofcarbondioxide, oxygen,nitrogen,andwatersimilartotheEarth’satmosphere,wehaveaverygoodcandidate foranotherhabitableworldsimilartoEarth. Itwillmostlikelytakelargertelescopestodefinitivelyfindlife.Ifastronomerscandeterminea moleculeoracombinationofmoleculesthatareonlyknowntocomefrombiologicalsources, andweobservethosemoleculesviatransitspectroscopy,wemaybeabletofindconcrete evidenceoflifeonexoplanets. 5