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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
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