“AllRoadsLeadtoTPF/Darwin”

SaraSeagerMIT

BiosignaturesandtheSearchforHabitableWorlds

WhyAstrobiology

 Theexoplanetatmosphereistheonlywaytoinferwhetherornotaplanetishabitableorlikelyinhabited

 Theplanetaryatmosphereisourwindowintotemperatures,habitabilityindicators,andbiosignaturegases

BiosignaturesandHabitablePlanets

Overview Review Introduction: Earth’s Biosignatures The Thermodynamics of Biosignatures The Search for Habitable Worlds

KnownPlanets1995

Based on data compiled by J. Schneider

KnownPlanets1996

Based on data compiled by J. Schneider

KnownPlanets2000

Based on data compiled by J. Schneider

KnownPlanets2005

Based on data compiled by J. Schneider

KnownPlanets2010

Based on data compiled by J. Schneider

Planets 2000

Planets 2005

Planets June 14 2010

Planet Candidates June 15 2010

KeplerPlanetCandidatesannouncedJune15,2010

AtmosphereInterpretaRon

H2OandCH4intransmissionfromHSTSwainetal.(2008)SeealsoGrillmairetal.2008.

IdenficaRonofatomsandmolecules

Day‐nighttemperaturegradients

Possiblevariability

Advancesinretrievaltechniques

SeeSeagerandDemingARAA2010

OverviewPoints

 MonumentalexoplanetachievementsweremadedespitewidespreadskepRcism

 Thehugepromiseforthefutureisbasedontheachievementsofthepastdecade+

Keepthisinmindfortherestofthetalk

BiosignaturesandHabitablePlanets

Introduction: Earth’s Biosignatures The Thermodynamics of Biosignatures The Search for Habitable Worlds

Earth,Venus,Mars

1DmodelsfromVikkiMeadowsVirtualPlanetaryLaboratory

Earth,Venus,Mars

1DmodelsfromVikkiMeadowsVirtualPlanetaryLaboratory

Earth’sSpectrum

Turnbulletal.2007

PearlandChristensen1997

S. Seager

InsRtuteforAdvancedStudy,Princeton,July2002

VegetaRonasaSurfaceBiomarker

S. Seager

S. Seager

VegetaRonasaSurfaceBiomarker

TheVegetaRonBiosignature

•  ChlorophyllcausesstrongabsorpRonatwavelengthsshorterthan0.7µm

•  Lightscaceringinairgapsbetweenwater‐filledplantcellscausesstrongredreflectance

•  Plantsabsorbenergyatshortwavelengthsforphotosynthesis;reflectandtransmitradiaRonatlongwavelengthsforthermalbalance

Seageretal.2005DatafromClark1993

EarthBiosignatureSummary•  O2/O3:thesmokinggun•  N2O:biologicalbutweaksignature

•  H2O:evidenceforliquidwater

•  CH4:biological/abiological

•  (VegetaRonrededge)

But,wearestuckinaworldofterracentricbiosignatures.

BiosignaturesandHabitablePlanets

Introduction: Earth’s Biosignatures The Thermodynamics of Biosignatures The Search for Habitable Worlds

NothingwouldbemoretragicintheAmericanexploraRonofspacethantoencounteralienlifeandfailtorecognizeitNRCreport2007

ConstraintsforLifeintheUniverse

AllLife

Liquidwater

Carbon‐based

ChemicalPotenRalEnergy

biologist

chemist

physicist

CH2O→CO2

Fuels

Redo

xPo

tenR

al(V

)

Oxidants

H2→H+ H+→H2

CO2→CH2O

NH4+→N2

N2→NH4+

CH4→CO2 CO2→CH4

H2S→SO42‐

SO42‐→H2S

O2→H2OH2O→O2

N2→NO3‐

NO3‐→N2

Nottoscale

ElectronTower

AkerLane,NatureMay2006

CH2O→CO2

Fuels

Red

oxPoten

Ral(V)

Oxidants

H2→H+ H+→H2

CO2→CH2O

NH4+→N2

N2→NH4+

CH4→CO2 CO2→CH4

H2S→SO42‐

SO42‐→H2S

O2→H2OH2O→O2

N2→NO3‐

NO3‐→N2

Nottoscale

CH2O→CO2

Fuels

Redo

xPo

tenR

al(V

)

Oxidants

H2→H+ H+→H2

CO2→CH2O

NH4+→N2

N2→NH4+

CH4→CO2 CO2→CH4

H2S→SO42‐

SO42‐→H2S

O2→H2OH2O→O2

N2→NO3‐

NO3‐→N2

Nottoscale

ElectronTower

AkerLane,NatureMay2006

BiosignatureThermodynamics

•  MetabolicreacRonsareredoxreacRons•  TheGibbsfreeenergyisusedtodeterminetheenergyyieldofareacRon

•  Recall:theGibbsfreeenergyisanenergypotenRal

•  TheenergypotenRalcanbeconvertedintovoltsviatheNernstequaRon.

See“BiologicalThermodynamics”byD.T.Haynie.

O2,H2,CO2,N2,N2O,NO,NO2,H2S,CH4,SO2,H2O,NH3

AllEarth‐basedmetabolicbyproducts

Gaseousmetabolicbyproducts

Unique

Generatedbygeologyor

photochemistry

Nothighlysolubleinocean

Notrapidlyassimilated

SeagerandSchrenk,“AnAstrophysicalViewofEarth‐BasedMetabolismsubmicedtoAstrobiology,.

SupportedbyFQXI

H2,CO2,H2S,CH4,SO2

O2,O3,N2O

Differentatmospheres/stellarUVcouldhavedifferentbiosignatures.

RadiaRvetransfer

AtmosphericComposiRon

Chemicalequilibrium/disequilibrium

Photochemistry

Atmosphericescape

AtmosphericcirculaRon

ConnecRonwithobservaRons

Clouds

Biosignatures

BiosignatureFramework • Foraspectralfeaturetobesignificant,whatistherequiredbiosignatureflux?

• ThisisnotonlyaradiaRvetransferproblem,butalsorelatedtophotochemistrysourcesandsinks,andputaRvechemistryoftheplanetcrustandatmosphere

• Realitycheck:converttobiomassbyequaRontheGibbsfreeenergy(yield)tomaintenanceenergyoftheorganism

Seageretal.inprep.FigurefromDeWit

BiosignatureSummary

•  Lifeusesandexploitschemicalenergygradients

•  ReacRonsthatareenergeRcallyfavorablebutkineRcallyinhibited

•  ThereisaquanRtaRvepathforwardforredoxbiosignaturefluxesinthecontextofatmosphericradiaRvetransferandchemistrymodels–givesachancetofindnewbiosignatures.

BiosignaturesandHabitablePlanets

Introduction: Earth’s Biosignatures The Thermodynamics of Biosignatures The Search for Habitable Worlds

RequirestechnologyinvestmentsAndnewspace‐basedfaciliRes

Prong1:TranrsiRngplanetswithafocusonMdwarfs

Prong2:directimagingofF,G,Kdwarfs

Two‐ProngedStrategy

Fast‐trackground‐based,andexisRngspaceassets

TransitSurveyTelescopes

TESSconcept6to9lensesonthesameplaqorm

CNES/Corot30cmmirrorPolarorbit

NASA/Kepler1mapertureEarth‐trailingorbit

ExoplanetSatconceptAtripleCubeSatconstellaRonofnanosats

PlatosciencepayloadUnderstudybyESO

Allroadsleadto…TerrestrialPlanetFinder/Darwin

DirectImaging

Marois,MacIntosh,Doyonetal.2008

A5V40pcPlanetsat:24,38,and60AUPlanet‐starcontrast104or105

Direct Imaging Telescope

Diffractedlightproblem

Direct Imaging Telescope

DiffractedlightsoluRons

…requireanearperfecttelescope

Cash2006

Cash2006

Ledby RemiSoummerandWebCashRecentSPIEpaper R.A.Brown,I.Jordan,A.Roberge,T.Glassman,A.Lo,S.Seager,L.Pueyoandothers

Technicalissues 70mocculterat70,000km StaRonkeeping ‐notopRmizedatvisible‐interesRngfeaturesnearamicron undersamplingofPSFatvisible‐limitstohighS/N limitedRme‐9%ofJWSTRme,limitssearchtoabout30stars

Principleofastarshadeonaseparatespacecraktoblockthelightfromthestar,whileallowingthelightfromanexoplanettopasstheedgeoftheocculterunimpeded.NorthrupGrumman

SeetheNASA‐sponsoredstudiesTHEIA(ledbyDavidSpergel),NWOledbyWebsterCash.SeeCash2006

SimulaRonsfora12‐dayobservingRmeforasuperEarthorbiRngasun‐likestarat10pc.

R=1000binneddowntoR=200

R.Soummeretal.SPIEinprep.ModelsbyS.Seager

SearchforHabitableWorldsSummary

•  TransitsordirectimagingwillprovideavaluablehandfulofpotenRallyhabitableplanets

•  VastresourcesintermsoftelescopeRmefortransitsandtechnologydevelopmentforspace‐baseddirectimagingareneeded

•  Anear‐termTerrestrialPlanetFinderpossibilityistheocculter+theJWST

A`

SummaryBiosignaturegoal:understandpossible

metabolicbyproductsandtheirlifeRmesonnon‐Earth‐likeexoplanets NWO

TransiRngexoplanets:findthemviaground‐basedorspacebasedtransitsearches.

MeasurespectraoftransiRngsuperEarthsorbiRngMstarsusingtheJamesWebbSpaceTelescope

DirectimagingfromspacetofindandcharacterizetrueEarthanalogs.Theexternalocculterispromisingtechnologytoblockoutstarlightofasun‐likestartoalevelof10billionatvisiblewavelengths

seagerexoplanets.mit.edu

KeplerDataBriceDemory (EAPSpostdoc)JoshCarter (Physicspostdoc)K.Berry (PhysicsUROP)K.Singh (PhysicsUROP)

ExoplanetAtmospheresandInteriorsB.Benneke (Aero/Astrogradstudent)M.Braunstein(EAPSgradstudent)R.Hu (EAPSgradstudent)M.Nikku (EAPSpostdoc)A.‐M.Piso (PhysicsUROP)L.Rogers (Physicsgradstudent)J.DeWit SupAeromastersintern

ExoplanetSatJ.Villasenor (Kavli)G.Farmer (EAPSgradstudent)C.Pong (Aero/Astrogradstudent)M.Smith (Aero/Astrogradstudent)M.Knapp (Aero/AstroUROP)B.Stavely (Aero/AstroUROP)

ThankyoutomystudentsandpostdocsSupportedbyMIT,NASA,andFQXI