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Biomarkers in terrestrial planet atmospheres

Super-Earths & Life

a fascinating cross-disciplinary puzzle

Lisa KalteneggerMPIA/Harvard UniversityIAUS276, Oct 15, 2010

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The Pale Blue Dot

Voyager image, 4 billion km away

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a dot of light = astronomyWe will never know how to study by any means the chemical composition of starsAuguste Comte (1835)

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RV & Transits: density

Torres 2008

Fortney, 2007Sasselov 2007

Zeng & Sasselov (in press)

5NEXT STEP NOW

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Signs Of Life On An Earth-like Planet

Vegetation ?

Plantproduct

Surface features e.g.Plantlife

Bacteria

ob

serv

ed

WaterOxygen Carbon

dioxide

Methane

Nitrousoxide

Ozone

Needed for life

Primordial; & bacteria product

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Visible spectrum of Earth

Observed Earthshine, reflected from dark side of moon.Ref.: Kaltenegger et al 2007, ApJ 574, 2007

see also e.g.: Montanez-Rodrigez 2005, 07, Arnold 2002, 06, 09; Turnbull 06

Rayleigh

Ozone O3

Chlorophyll ?

Oxygen O2

Water H2O

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Earth IR-emission

Kaltenegger, Traub, Jucks 2007 (ApJ)

TES data; Christensen 2004

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Thermal structure rocky Exo-P atmosphere• well mixed, dry transparent atmosphere

∂T/∂z = -g/cp convection Earth : -9.8 K/km, Mars -5 K/km, Venus -10 K/km, Titan 1.3 K/km

REALITY: atmosphere absorbs & reemits in thermal IR

Radiative equilibrium profile & convection

mid-atmosphere: UV (λ < 360 nm) O3: A) stratosphere

high-atmosphere: 10-2 - 10-4 Pa: EUV (λ < 200 nm) photolyse any molecules, heats low density gas : B) thermosphere

Temperature

Alti

tude

~10-4 -Pa

EUV

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TitanEarth

Giants

Titan

Earth

13Selsis 2007 (model Tinetti)

Features: 1) observables & 2) unique ?

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Transit Geometryz

T( z, )

h is the effective height of an opaque

atmosphere:

h() = ∫ (1-T) dz

SoR() = R0 + h()

h ≈ T/(g )

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Explore Planets - EGP

Atmosphere by transits... HD189733b (Tinetti07, Swain08)Earth (Palle 09, Kaltenegger 09)

2007 +

16Kaltenegger & Traub ApJ 2009Palle et al. Nature 2009Data: ATMOS B. Irion 2002

Earth Primary Transit: collect transmitted starlight

SNR = N1/2(tot) * 2Rp h / Rs2

2002/2014+ ?

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Earth: ATMOS-3:Transmission validation in far-IR

ATMOS-3 transmission of sunlight through Earth’s atmosphere, measured with a fast FTS on Shuttle

yellow = model

Fit is close, but line wings are not perfect, perhaps owing to line-mixing effects in strong bands.

Note low transmission below 10 km.

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JWST Best Earths: Closest Stars/Transit

Kaltenegger & Traub ApJ 2009

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Line of Evidence

FIND

INTERIOR

ATMOSPHERE

LIFE ?

SPECTRAL FINGERPRINT

WHAT KIND

FORMATION

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MODEL

STAR: FluxPLANET:

CompositionWater delivery OutgassingTectonicGeoch. CycleMagnetosphere

= ATMOSPHERES

SPECTRAL Fingerprint

DATA

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Gravity, size, composition LK

• Photochem• (based on Kasting 1986)

• Extended Photochemistry (based on Pavlov 2000)

• Radiative Transfer • (based on SAO98, Traub & Stier 1979)

LK

LK

LK

Planet interior,outgassing RF,WH

biota, host stars, geo.cycles SR,LK

Clouds, Hazes, Escape

Kaltenegger et al 2007, 2009, 2009b ApJ

Exo-P = Rocky ExoPlanets CodeL. Kaltenegger

Detectable features

Different evolution state / age / mass / etc.

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Biomarkers & spectra change over time IMPORTANT: e.g: Surface temp change, cloud! coverage

Kaltenegger et al ApJ 2007

25Kaltenegger et al 2007 ApJmid IR (5-20m): Res = 25

26Kaltenegger et al 2007 ApJ

VIS (0.4-1.2 m): Res = 150

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Habitable Zone – water liquid on surface of Earth-analog

Selsis et al 2007, Kaltenegger et al 2008, Seager et al 2008, Miller-Ricci et al 2008,...

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Climate Stabilization : Carbonate – Silicate Cycle Walker et al. 1981

Ts ↓ water cycle ↓ weathering ↓

Ts ↑ Greenhouse effect ↑ PCO2 ↑

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Pinatubo – explosive exo-volcanos ? Res = 150, SNR calc. for JWST (pure photon noise, template input for instruments)

Kaltenegger & Sasselov (ApJ 09), Kaltenegger & Henning (ApJ 2010)

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Goldilocks ZoneGl 581c... HOT, Gl581d COLD

Selsis et al 2007, Kaltenegger et al 2010, von Paris et al 2010, Seager et al 2008, Miller-Ricci et al 2008,...

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Test case: Gl 581d

Kaltenegger, Segura & Mohanty 2010 (ApJ)

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Test case: Gl 581d

Kaltenegger, Segura & Mohanty 2009 (ApJ)

Gl 581d spectra& star/planet contrast ratioKaltenegger, Mohanty & Segura ApJ 2010

Spectra (0.1 - 100 m): Resolution 15033

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Gl 581d Transit Spectrain planetary radius Kaltenegger, Mohanty & Segura ApJ 2010Spectra (0.4 - 40 m): Resolution 150

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Wade Henning, Harvard, EPS

Roger Fu, Harvard, EPS

Sarah Rugheimer, Harvard, Astroph.

Leah Kilvert, Un. Victoria, Astroph.

Exo-P = current students

OPEN (AAS job registry):2 Postdoc & 1 PhD posMPIA Heidelberg

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Science Case: ELT,GMT,TMT, JWST(SPITZER, SPICA, SMALL SPACE MISSIONS (e.g TESS))

Are there other worlds like ours? Epicurius (c. 300 B.C)

2300 years and counting.... Let‘s find out

Not just FIND... (POS VIEW )

Characterize rocky exoplanets- composition 0 – 20 years- habitability 5 – 20 years- stage of evolution 5 – 30 years- geochemical cycles 5 – 20 years- HR Diagram of planets 5 – 20 years

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WHY ?

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Summary• First potentially Habitable Super-Earth found

• JWST, ELT/GMT/TMT & new small missions• Models: - instrument design, data analysis

- explore the underlying physics• Earth: a rosetta stone for exoplanets

CreditNAI, Harvard Origins of Life

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Super Earth around M star HZGl 581d: Earth Atmosphere, 2.63 bar, 1.8x Earth gravity

Tidally locked planet (rapidely rotating planet comparison line (shown in grey))Scenario 1: high heat transport from day (60%) to night side (40%)

CO2

O3

CH4

H2OCO2

Kaltenegger, Segura, Mohanty ApJ sub (ApJ)