TRAPPIST-1 Press Release

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FrequentlyAskedQuestionsforInformalLearningEnvironments

Foradditionalinformation,besuretocheckouttheNASAExoplanetExplorationFAQandGlossary.

• NASAExoplanetExplorationFAQ-https://exoplanets.nasa.gov/faq/• NASAExoplanetExplorationGlossary-https://exoplanets.nasa.gov/glossary/

TRAPPIST-1FAQ1. Whatmakesthisdiscoveryspecial?Therearemanyreasonswhythisdiscoveryistrulyspecial.ThediscoveryofsevenEarth-sizedplanetsinthesamestarsystemhasprofoundimplicationsforoursearchforhabitableworldsoutsideofoursolarsystem.Ontopofthat,thisisthefirsttimethatpeoplehavediscoveredastarsystemwithmorethanoneplanetinthehabitablezonethatwecanexaminewithtransitspectroscopy.Transitspectroscopyisthemeasurementofaplanet’satmospherewhileittransitsitshoststarviastudyinghowthelightfromthehoststarbehavesasitpassesthroughtheplanet’satmosphere.Bybreakingupthislightintoitsconstituentcolorsviaaspectrograph,wecanlearnaboutthechemicalcompositionoftheplanet’satmosphere.Additionally,thereasonablylowactivitylevelofthecentralstarmeanstheyaremorelikelytobeabletosupportlife.Finally,thesystemisreallyclose,only39light-yearsaway.Thatmakesiteasierforustolearnmorewithourcurrentobservatories–Spitzer,Hubble,Kepler,andground-basedtelescopes–andpossiblylearntheanswerstomoreburningquestionswiththesoon-to-comeJamesWebbSpaceTelescope.2. WhyisthisplanetarysystemcalledtheTRAPPISTsystem?TheTRAPPISTsystemisnamedaftertheTRAnsitingPlanetsandPlanetesImalsSmallTelescope(TRAPPIST)robotictelescopes.TherobotictelescopesarelocatedinChileandMorocco,buttheyareledbyastrophysicistsinBelgium.Becausethesetelescopesdiscoveredthefirstexoplanetsinthesystemin2016,thesystemwasnamedTRAPPIST-1.Thenumber1referstothefactthatthisisthefirstsystemnamedafterthesetelescopes.Theprogramname(TRAPPIST)isanodtothemonasticorderintheBelgiumregion,knownbymanyforbrewingTrappistbeers.

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3. HowdidwefigureoutthereweremoreplanetsintheTRAPPIST-1system?

WeoriginallyfoundplanetsintheTRAPPIST-1systembylookingatvariationsinlightcomingfromthestar.Thelightgetsdimmerandformsawigglepatternwhenplanetstransit,orpass,betweenthestarandtheEarth.Thepatternchangesdependingonhowmanyplanetsthereare,howfasttheyorbit,andotherfactors.NASA’sSpitzerSpaceTelescopewasabletoobservethesystemformultipletransitsatahigherprecisionthantheTRAPPISTtelescopecould.Sowhenthewigglepattern—whichwasactuallyatleastsevenplanetswigglingontopofeachother—isobservedlongenoughathigh-enoughprecision,wecandisentanglethesignaturesoftheindividualplanets.OfcoursetherecouldbeevenMOREplanetshiddenbeyondourdetectionlimit:theirorbitsmaybetoolong,theymaybetoosmalltobedetected,ortheymaybeexactlyinresonancewithoneoftheexistingplanetswefound.4. WhywasSpitzerlookingatasystemwealreadyknewabout?TheSpitzerSpaceTelescopewaslookingattheTRAPPIST-1systembecauseitcouldget*very*accuratemasses,densities,andotherpropertiesthatareimpossiblefromeventhemoststableground-basedobservatory.TheEarth'satmospherelimitsourultimateabilitytodetecttheseproperties.Italsolimitsourabilitytodetectthegasesthatmightbepresentaroundanexoplanet(notably,water.)Furthermore,Spitzerisaninfraredtelescope,sotherearespecificpropertiesitcandeterminethatcannotcurrentlybeobservedelsewhere,evenbyNASA’sHubbleSpaceTelescope.Onceweknewtherewereplanets,therewasalottobegainedbydoingadeeperstudywithSpitzertolearnmoreaboutthem.Thisdiscoverystartedwithaground-basedfacility-TRAPPIST–thatlookedatalargenumberofstars,searchingforexoplanets.Thenwepointedspace-basedfacilitieslikeSpitzerandHubbleontheTRAPPISTsystembecausetheTRAPPISTtelescopefoundsomethinginteresting.Lotsofastronomerscompeteforalimitedamountoftimetostudyobjectswithspacetelescopes.Sospacetelescopesgenerallydonotstareatastarforlongperiodsoftimelookingforexoplanetsunlessanothertelescopehasproduceddataindicatingtheymightbethere.Wecan’tlookateverythingwithSpitzer/Hubble,butoncewehaveapromisingtarget,thecaseforusingSpitzerorHubbletoobserveasystembecomesstronger.SpitzerjusthappenedtofindadditionalplanetsintheTRAPPISTsystemwhileitwasobservingtheknownexoplanetsoriginallyspottedbytheTRAPPISTtelescope.

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GeneralExoplanetFAQ1. Howareexoplanetsnamed?Exoplanetsarenamedaftertheirparentstar,andgivenlowercaselettersbasedonwhentheyarediscoveredandontheirdistancefromtheirhoststar.Forexample,TRAPPIST-1AistheTRAPPIST-1star.TRAPPIST-1bandTRAPPIST-1cwerethefirstplanetsdiscoveredaroundthisstar,with1bbeingtheclosesttothestarand1cbeingthenextclosest.Thethirdplanetoriginallythoughttobepartofthesystemturnedouttoactuallybethreedifferentplanets.Sincethiswascaughtearly,thenewplanetswerenamed1d,1e,1f,1g,and1h,goingfromclosesttofarthest.IfwediscoveredaneighthplanetorbitingTRAPPIST-1Afiveyearsfromnow,itwouldbecalledTRAPPIST-1i,regardlessofitslocation.2. Whatisanexoplanet?Thetermexoplanetoriginallycomesfromextra-solarplanet,whichjustmeansaplanetorbitingastarotherthanourSun.Otherstarsarereallyfaraway.Astar’sbrightnessmakesitincrediblydifficulttodetectanearbyorbitingbody.Giventheseobservationaldifficulties,exoplanetswerenotdetecteduntilquiterecently(theearly1990’s).Astronomersneededtocreateseveralingenioustechniquestofindandstudythem.Nowtherearethousandsofconfirmedexoplanets,thousandsmorethatarecandidateexoplanetsawaitingconfirmationwithmoredata,andfuturemissionsdevotedtofindingandcharacterizingthem.3. HowmanyEarth-sizeplanetshavewefoundsofar?Atthetimeofthisdiscovery,therewereapproximately340confirmedterrestrialplanetsknown.TheseareplanetsthatarearoundthesamesizeastheEarth(source:NASA’sExoplanetArchive).Thisnumbercomprisesabout10percentofallconfirmedexoplanets.Theothertypesofexoplanetsareicegiants(likeNeptuneandUranus),gasgiants(likeJupiterandSaturn),andsuper-Earths(planetsthatfallbetweenNeptune/UranusandEarthinsize,ofwhichtherearenocounterpartsinoursolarsystem).

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4. Whatisthehabitablezone?

Habitablemeanssuitableforlife.TheoneconstantforlifeonEarthistheexistenceofliquidwater.So,thesimplestanswertothisquestionisthehabitablezoneistheregionaroundastarwhereliquidwatercanexist.Ifanexoplanetistooclose,itwillbetoohotandwaterwillevaporate.Ifanexoplanetistoofar,itwillbetoocoldandwaterwillfreeze.Giventhatstarscomeinarangeofsizesandtemperatures,thehabitablezonewillchangedependingonthetypeofstararoundwhichanexoplanetorbits.AnothercommondefinitionforhabitablezoneiswheretheaveragetemperaturefallsinbetweentheaverageonthesurfaceofVenusandMars,NOTaccountingforatmosphericeffectslikeVenus'srunawaygreenhouse.Wedonotyetknowmuchabouttheatmospheresofmostofthediscoveredexoplanets,andhabitabilityisacomplicatedconceptbecauseanatmospheregreatlyimpactswhetherornottheexoplanetistoohot,toocold,orjustrightforliquidwatertoexist.Includingatmosphericeffectsaretrulycriticalforactuallyunderstandingwhetherornotanexoplanetishabitableandwillbecriticalinfuturestudiesofhabitability.Ofcourse,beinginahabitablezonedoesnotguaranteehabitability(e.g.,theMoon).Beingoutofthehabitablezonedoesnotnecessarilymeantheplanetormoonisnothabitable(e.g.,Europa,amoonofJupiterthatcouldhaveliquidwater).Butthehabitablezoneisapowerfulindicatorofwhereliquidwatermightmosteasilybefound.Hence,theideaofahabitablezoneisaguideforastronomerssearchingforplacesinouruniversewherelifemightexist.5. HowmanyEarth-sizeplanetshavewefoundinahabitablezone?Atthetimeofthisdiscovery,thereweresixexoplanetslabeledas“potentialEarths,”basedontheirsizeandlocationwithintheirsystems’habitablezone.Thenewdiscoveriesbringthetotaluptonine.6. Whydowelookforexoplanets?OneofNASA’sbiggoalsinthestudyoftheuniverseistoaddressthequestion,“AreweAlone?,”bysearchingforlifeonplanetsaroundotherstars.Thisquestion,ponderedbyhumansforcenturies,isjustnowbeginningtobedirectlyaddressed,thankstonewtechnologiesintelescopesandnewstrategiesinsearchingforexoplanets.Beforewecandirectlyanswertheprimaryquestion,wefirsthavetofindtheexoplanetsandbegintocharacterizetheirproperties.Forexample,aretheyEarth-sized,inthehabitablezone,andhabitableasdefinedbythematerialintheiratmospheres?Thesearethequestionswearejustnowbeingabletoanswer.

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7. WhatdowemeanbyEarth-likeexoplanets?“Earth-like”iscommonlyusedtorefertoexoplanetsthatareaboutthesamesizeasEarthANDresideinthehabitablezone.Aswelearnmoreaboutexoplanets,weareabletousenewdatatoreducethenumberofexoplanetsthatmaytrulybeEarth-like.IntheTRAPPISTsystem,wehavegoodinformationonthemassesandsizesoftheexoplanets.Thisinformationcanprovideameasurementofthebulkdensitiesoftheexoplanets.Thebulkdensity(mass/volume)cantellusiftheexoplanetiscomposedofrock,metal,water,orgas.Ultimately,totrulytellifanexoplanetisEarth-like,weneedtoknowifitcansupportlifeasweknowit.Todothat,weneedtotakedetailedspectraoftheiratmospherestodiscoverwhattheatmospheresaremadeof.Ifwefindexoplanetatmosphereswithamountsofcarbondioxide,oxygen,nitrogen,andwatersimilartotheEarth’satmosphere,wehaveaverygoodcandidateforanotherhabitableworldsimilartoEarth.Itwillmostlikelytakelargertelescopestodefinitivelyfindlife.Ifastronomerscandetermineamoleculeoracombinationofmoleculesthatareonlyknowntocomefrombiologicalsources,andweobservethosemoleculesviatransitspectroscopy,wemaybeabletofindconcreteevidenceoflifeonexoplanets.