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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.
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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.
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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).
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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.
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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.
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