Biomarkers in Super Earth Atmospheres: Photochemical Responses

John Lee Grenfell Zentrum für Astronomie und Astrophysik, Technische Universität (TU) Berlin

1,2Rauer, H.,1Gebauer, S., 2v, Paris, P.,2Cabrera, J.,1Godolt, M.,1Palczynski, K. 3Belu, A.,3Selsis, F.,3 Hedelt, P. (1) TU-Berlin, (2) German Space Agency (DLR-PF) Berlin, (3) Uni. Bordeaux

Grenfell et al. II. Chemical Responses (in preparation)

Grenfell et al. II. Chemical Responses (in preparation)

-Earthlike biomass

-one bar surface pressure

-vary gravity (1g, 3g)

-vary M-star class (M0 to M7)

Overview of Talk

Motivation

Ozone as an atmospheric biomarker

Models and tools

Super-Earth scenarios

Results

Conclusions

Motivation

Understand and predict atmospheric spectra of Super-Earth planets in the HZ of M-stars

Source: 2D Model SOCRATES

Alti

tude

(km

) Atmospheric Biomarkers: Earth's Ozone Layer

Ozone (O3) produced from oxygen

which itself comes mainly from biology ...so ozone is a biomarker (life-indicator).Ozone is easier to detect spectrally than oxygen.

„Good“ Ozone

O2+UV-->O+O NEED UVB

O+O2+M-->O

3+M

„Bad“ Ozone – smog

~9ppm

“Bad” (Smog) Ozone formed:CO+2O

2-->O

3+CO

2

“Good” Ozone formed:O2 +hv--> 2O

O2+O+M-->O

3+M

30km

10km

~9x10-6 by volume

Hei

ght

Ozone Concentration

Chlorine reactions destroy ozone

Nitrogen reactionsdestroy ozone

Ozone in Earth's Atmosphere

30km

70kmOZONE CONTINUOUSLY FORMED AND DESTROYED

MODELS AND TOOLS: CLIMATE-CHEMISTRY MODELGlobal Mean Column Model with coupled radiation and chemistry

(Kasting et al., 1984, Segura et al., 2003; Grenfell et al., 2007: Rauer et al. 2010 submitted)

CLIMATEground to mid-

mesosphere

StratosphereSolve Radiative

Transfer

TroposphereWet adiabatic convection

CHEMISTRYground to mid-

mesosphere

Solve Continuity Eq.

55 species220 reactions

Biomarker chemistry

Startvalues

StartValues

Temperature, water

Radiative Gases

MODELS AND TOOLS: CLIMATE-CHEMISTRY MODELGlobal Mean Column Model with coupled radiation and chemistry

(Kasting et al., 1984, Segura et al., 2003; Grenfell et al., 2007: Rauer et al. 2010 submitted)

CLIMATEground to mid-

mesosphere

StratosphereSolve Radiative

Transfer

TroposphereWet adiabatic convection

CHEMISTRYground to mid-

mesosphere

Solve Continuity Eq.

55 species220 reactions

Biomarker chemistry

Startvalues

StartValues

Temperature, water

Radiative Gases

OUTPUT TO LINE-BY-LINE

SPECTRAL EMISSION MODEL

(SQuIRRL) (Schreier and Böttg

er, 2003)

Pathway Analysis Program (PAP)

PAP

Lehmann 2004Grenfell et al. (2006)

Atmospheric model:chemical ratesand concentrationsover two timesteps

Identify and quantifychemical pathwaysfor e.g. ozone

Hence understand changes in ozone photochemistry

30km

10km

Hei

ght

Ozone Concentration

Chlorine reactionsdestroy ozone

HOW PAP WORKSCl+O

3-->ClO+O

2

ClO+O-->Cl+O2

----------------------O

3+O-->2O

2

5% O3 loss 30km

Super-Earth Scenarios

Earth (M)

Assume an Earthlike development

Rauer et al. (2010) submittedGrenfell et al. (2010) in preparation

M82400K

M03800K

M4.53400K

10M (3g)

Results: Effect of Stellar Spectrum on Temperature

M8M0

ADL

Earth

M7M6M5

RESULTS: Effect of M-Star Class on Planetary Temperature Profile

Less UV-B: less jH2O, less OH, more CH4

(and H2O) Stratospheric Heating

M4

M7M0

warmer stratosphere, sofaster Chapman sink: O+O32O2

RESULTS: Effect on Ozone of changing M-star spectrum

-higher spectral class-less UV-less ozone

Sun

M7

M0

Rauer et al. (2010) submitted

Results: Effect on Ozone of Increasing Gravity

Earth

Super-Earth (3g)

1g3g

Effect on Ozone of increasing gravity

Rauer et al. (2010) submitted

Grenfell et al. Paper II: OZONE RESPONSES Column (Production – Loss) in molecules cm-2

Earth Earthlike around M7 star

2E12 4E10 PRODUCTION O

2+hv-->O+O

O+O2+M-->O

3+M

CHAPMAN (99%)

PRODUCTION CO+2O

2-->O

3+CO

2

SMOG (~50%)

LOSS O

3+CO-->O

2+CO

2

O3 REDUCTION (~35%)

Grenfell et al. (2010) in preparation

LOSSNOx, HOx destructionCLASSIC CYCLES (~50%)

Grenfell et al. Paper II: OZONE RESPONSES Column (Production – Loss) in molecules cm-2

Earth Earthlike around M7 star

2E12 4E10 PRODUCTION O

2+hv-->O+O

O+O2+M-->O

3+M

CHAPMAN (99%)

PRODUCTION CO+2O

2-->O

3+CO

2

SMOG (~50%)

LOSS O

3+CO-->O

2+CO

2

O3 REDUCTION (~35%)

Grenfell et al. (2010) in preparation

LOSSNOx, HOx destructionCLASSIC CYCLES (~50%)

Weaker UV-B fro

m M-star

means Chapman production (needs jO 2) - f

ails

M7 Ozone produced from smog mechanism

Conclusions

Essential to couple climate and chemistry

Ozone photochemistry may be smog-dominated(whereas Chapman-dominated on Earth) for earthlikeplanets in the Habitable Zone of M-stars