STABILITY OF CO2 ATMOSPHERES ON DESICCATED M DWARF EXOPLANETS

We investigate the chemical stability of CO_2-dominated atmospheres of desiccated M dwarf terrestrial exoplanets using a one-dimensional photochemical model. Around Sun-like stars, CO_2 photolysis by Far-UV (FUV) radiation is balanced by recombination reactions that depend on water abundance. Planets orbiting M dwarf stars experience more FUV radiation, and could be depleted in water due to M dwarfs' prolonged, high-luminosity pre-main sequences. We show that, for water-depleted M dwarf terrestrial planets, a catalytic cycle relying on H_2O_2 photolysis can maintain a CO_2 atmosphere. However, this cycle breaks down for atmospheric hydrogen mixing ratios <1 ppm, resulting in ~40% of the atmospheric CO_2 being converted to CO and O_2 on a timescale of 1 Myr. The increased O_2 abundance leads to high O_3 concentrations, the photolysis of which forms another CO_2-regenerating catalytic cycle. For atmospheres with <0.1 ppm hydrogen, CO_2 is produced directly from the recombination of CO and O. These catalytic cycles place an upper limit of ~50% on the amount of CO_2 that can be destroyed via photolysis, which is enough to generate Earth-like abundances of (abiotic) O_2 and O_3. The conditions that lead to such high oxygen levels could be widespread on planets in the habitable zones of M dwarfs. Discrimination between biological and abiotic O_2 and O_3 in this case can perhaps be accomplished by noting the lack of water features in the reflectance and emission spectra of these planets, which necessitates observations at wavelengths longer than 0.95 μm.

[1]  Gautam Vasisht,et al.  Observations of Transiting Exoplanets with the James Webb Space Telescope (JWST) , 2014, 1411.1754.

[2]  Sushil K. Atreya,et al.  Stability of the Martian atmosphere: Is heterogeneous catalysis essential? , 1993 .

[3]  Christopher T. Reinhard,et al.  Low Mid-Proterozoic atmospheric oxygen levels and the delayed rise of animals , 2014, Science.

[4]  Y. Abe,et al.  Emergence of two types of terrestrial planet on solidification of magma ocean , 2013, Nature.

[5]  Tyler D. Robinson,et al.  ABIOTIC OZONE AND OXYGEN IN ATMOSPHERES SIMILAR TO PREBIOTIC EARTH , 2014, 1407.2622.

[6]  T. Encrenaz,et al.  Heterogeneous chemistry in the atmosphere of Mars , 2008, Nature.

[7]  Yuk L. Yung,et al.  Vertical transport and photochemistry in the terrestrial mesosphere and lower thermosphere (50–120 km) , 1981 .

[8]  Tyler D. Robinson,et al.  DETECTING OCEANS ON EXTRASOLAR PLANETS USING THE GLINT EFFECT , 2010, 1008.3864.

[9]  Raymond G. Roble,et al.  How will changes in carbon dioxide and methane modify the mean structure of the mesosphere and thermosphere , 1989 .

[10]  Guy Brasseur,et al.  Aeronomy of the Middle Atmosphere: Chemistry and Physics of the Stratosphere and Mesosphere , 1984 .

[11]  B. Mcbride,et al.  Thermodynamic Functions of Several Triatomic Molecules in the Ideal Gas State , 1961 .

[12]  Franck Selsis,et al.  Signature of life on exoplanets: Can Darwin produce false positive detections? , 2002 .

[13]  J. London,et al.  Ozone Photochemistry and Radiative Heating of the Middle Atmosphere , 1974 .

[14]  Sara Seager,et al.  PHOTOCHEMISTRY IN TERRESTRIAL EXOPLANET ATMOSPHERES. I. PHOTOCHEMISTRY MODEL AND BENCHMARK CASES , 2012, 1210.6885.

[15]  David C. Catling,et al.  Photochemical instability of the ancient Martian atmosphere , 2008 .

[16]  Michael B. McElroy,et al.  Stability of the Martian Atmosphere , 1972, Science.

[17]  Howard Isaacson,et al.  An Earth-Sized Planet in the Habitable Zone of a Cool Star , 2014, Science.

[18]  D. Hunten The Escape of Light Gases from Planetary Atmospheres , 1973 .

[19]  D. Hunten,et al.  An estimate of the present-day deep-mantle degassing rate from data on the atmosphere of Venus , 1970 .

[20]  Manuel López-Puertas,et al.  Non-Lte Radiative Transfer in the Atmosphere , 2001 .

[21]  Drake Deming,et al.  Earth as an extrasolar planet: Earth model validation using EPOXI earth observations. , 2011, Astrobiology.

[22]  J. Blamont,et al.  Stability of the Martian atmosphere: Possible role of heterogeneous chemistry , 1990 .

[23]  K. Covey,et al.  Spectroscopic Properties of Cool Stars in the SDSS , 2004 .

[24]  V. L. Orkin,et al.  Scientific Assessment of Ozone Depletion: 2010 , 2003 .

[25]  D. Crisp,et al.  Ground‐based near‐infrared observations of the Venus nightside: The thermal structure and water abundance near the surface , 1996 .

[26]  J. Drake,et al.  THE INTERACTION OF VENUS-LIKE, M-DWARF PLANETS WITH THE STELLAR WIND OF THEIR HOST STAR , 2015, 1504.06326.

[27]  Victoria Meadows,et al.  Biosignatures from Earth-like planets around M dwarfs. , 2005, Astrobiology.

[28]  Stanley P. Sander,et al.  NASA Data Evaluation: Chemical Kinetics and Photochemical Data for Use in Atmospheric Studies , 2014 .

[29]  P. Wine,et al.  Temperature‐dependent absorption cross sections for hydrogen peroxide vapor , 1988 .

[30]  B. Hapke,et al.  Mineralogy of Martian atmospheric dust inferred from thermal infrared spectra of aerosols , 2005 .

[31]  H. Lichtenegger,et al.  Coronal mass ejection (CME) activity of low mass M stars as an important factor for the habitability of terrestrial exoplanets. II. CME-induced ion pick up of Earth-like exoplanets in close-in habitable zones. , 2007, Astrobiology.

[32]  U. Gunten,et al.  Chemistry of Ozone in Water and Wastewater Treatment , 2012 .

[33]  F. Selsis,et al.  Potential biosignatures in super-Earth atmospheres II. Photochemical responses. , 2013, Astrobiology.

[34]  Jay A. Stein,et al.  An investigation of the effect of temperature on the Schumann‐Runge absorption continuum of oxygen, 1580–1950 A , 1966 .

[35]  J. Brinkmann,et al.  Spectroscopic Properties of Cool Stars in the Sloan Digital Sky Survey: An Analysis of Magnetic Activity and a Search for Subdwarfs , 2004, astro-ph/0403486.

[36]  Kevin France,et al.  High stellar FUV/NUV ratio and oxygen contents in the atmospheres of potentially habitable planets , 2013, 1310.2590.

[37]  D. Sasselov,et al.  THE ATMOSPHERIC SIGNATURES OF SUPER-EARTHS: HOW TO DISTINGUISH BETWEEN HYDROGEN-RICH AND HYDROGEN-POOR ATMOSPHERES , 2008, 0808.1902.

[38]  Andrew S. Ackerman,et al.  Precipitating Condensation Clouds in Substellar Atmospheres , 2001, astro-ph/0103423.

[39]  R. Luger,et al.  Extreme water loss and abiotic O2 buildup on planets throughout the habitable zones of M dwarfs. , 2014, Astrobiology.

[40]  J. Lean,et al.  The effect of temperature on thermospheric molecular oxygen absorption in the Schumann‐Runge Continuum , 1981 .

[41]  Kevin France,et al.  THE ULTRAVIOLET RADIATION ENVIRONMENT AROUND M DWARF EXOPLANET HOST STARS , 2012, 1212.4833.

[42]  M. Johnson,et al.  Carbon dioxide photolysis from 150 to 210 nm: Singlet and triplet channel dynamics, UV-spectrum, and isotope effects , 2013, Proceedings of the National Academy of Sciences.

[43]  David Harry Grinspoon,et al.  Implications of the high D/H ratio for the sources of water in Venus' atmosphere , 1993, Nature.

[44]  J. Kasting,et al.  CO2 condensation and the climate of early Mars. , 1991, Icarus.

[45]  B. Lindner Ozone on Mars: The effects of clouds and airborne dust , 1988 .

[46]  James F. Kasting,et al.  Bolide impacts and the oxidation state of carbon in the Earth's early atmosphere , 2005, Origins of life and evolution of the biosphere.

[47]  A. Anbar,et al.  A photochemical model of the martian atmosphere. , 1994, Icarus.

[48]  Edward W. Schwieterman,et al.  DETECTION OF OCEAN GLINT AND OZONE ABSORPTION USING LCROSS EARTH OBSERVATIONS , 2014, 1405.4557.

[49]  V. L. Orkin,et al.  Chemical Kinetics and Photochemical Data for Use in Atmospheric Studies: Evaluation Number 18 , 2015 .

[50]  W. Demore,et al.  Photochemistry of Planetary Atmospheres , 1998 .