Observing the Atmospheres of Known Temperate Earth-sized Planets with JWST

Nine transiting Earth-sized planets have recently been discovered around nearby late M dwarfs, including the TRAPPIST-1 planets and two planets discovered by the MEarth survey, GJ 1132b and LHS 1140b. These planets are the smallest known planets that may have atmospheres amenable to detection with JWST. We present model thermal emission and transmission spectra for each planet, varying composition and surface pressure of the atmosphere. We base elemental compositions on those of Earth, Titan, and Venus and calculate the molecular compositions assuming chemical equilibrium, which can strongly depend on temperature. Both thermal emission and transmission spectra are sensitive to the atmospheric composition; thermal emission spectra are sensitive to surface pressure and temperature. We predict the observability of each planet's atmosphere with JWST. GJ 1132b and TRAPPIST-1b are excellent targets for emission spectroscopy with JWST/MIRI, requiring fewer than 10 eclipse observations. Emission photometry for TRAPPIST-1c requires 5-15 eclipses; LHS 1140b and TRAPPIST-1d, TRAPPIST-1e, and TRAPPIST-1f, which could possibly have surface liquid water, may be accessible with photometry. Seven of the nine planets are strong candidates for transmission spectroscopy measurements with JWST, though the number of transits required depends strongly on the planets' actual masses. Using the measured masses, fewer than 20 transits are required for a 5 sigma detection of spectral features for GJ 1132b and six of the TRAPPIST-1 planets. Dedicated campaigns to measure the atmospheres of these nine planets will allow us, for the first time, to probe formation and evolution processes of terrestrial planetary atmospheres beyond our solar system.

[1]  J. Kasting,et al.  Habitable zones around main sequence stars. , 1993, Icarus.

[2]  Yuk L. Yung,et al.  High-temperature Photochemistry in the Atmosphere of HD 189733b , 2010 .

[3]  David Charbonneau,et al.  Design Considerations for a Ground-Based Transit Search for Habitable Planets Orbiting M Dwarfs , 2007, 0709.2879.

[4]  M. Marley,et al.  Line and Mean Opacities for Ultracool Dwarfs and Extrasolar Planets , 2007, 0706.2374.

[5]  M. R. Haas,et al.  TERRESTRIAL PLANET OCCURRENCE RATES FOR THE KEPLER GK DWARF SAMPLE , 2015, 1506.04175.

[6]  Dimitar Sasselov,et al.  PREDICTIONS OF THE ATMOSPHERIC COMPOSITION OF GJ 1132b , 2016, 1607.03906.

[7]  G. Marcy,et al.  THE MASS–RADIUS RELATION FOR 65 EXOPLANETS SMALLER THAN 4 EARTH RADII , 2013, 1312.0936.

[8]  C. Goldblatt.  Habitability of waterworlds: runaway greenhouses, atmospheric expansion, and multiple climate states of pure water atmospheres. , 2015, Astrobiology.

[9]  Joseph E. Rodriguez,et al.  A temperate rocky super-Earth transiting a nearby cool star , 2017, Nature.

[10]  P. Hauschildt,et al.  MODEL ATMOSPHERES OF VERY LOW MASS STARS AND BROWN DWARFS , 1997 .

[11]  D. Catling,et al.  Common 0.1 bar tropopause in thick atmospheres set by pressure-dependent infrared transparency , 2013, 1312.6859.

[12]  Drake Deming,et al.  REPEATABILITY AND ACCURACY OF EXOPLANET ECLIPSE DEPTHS MEASURED WITH POST-CRYOGENIC SPITZER , 2016, 1601.05101.

[13]  Jean-Baptiste Madeleine,et al.  GLIESE 581D IS THE FIRST DISCOVERED TERRESTRIAL-MASS EXOPLANET IN THE HABITABLE ZONE , 2011, 1105.1031.

[14]  D. Saumon,et al.  The Evolution of L and T Dwarfs in Color-Magnitude Diagrams , 2008, 0808.2611.

[15]  Sanford Gordon,et al.  Computer program for calculation of complex chemical equilibrium compositions , 1972 .

[16]  D. Charbonneau,et al.  THE OCCURRENCE OF POTENTIALLY HABITABLE PLANETS ORBITING M DWARFS ESTIMATED FROM THE FULL KEPLER DATASET AND AN EMPIRICAL MEASUREMENT OF THE DETECTION SENSITIVITY , 2015, 1501.01623.

[17]  Mark S. Marley,et al.  Synthetic Spectra and Colors of Young Giant Planet Atmospheres: Effects of Initial Conditions and Atmospheric Metallicity , 2008, 0805.1066.

[18]  Joanna K. Barstow,et al.  Habitable worlds with JWST: transit spectroscopy of the TRAPPIST-1 system? , 2016, 1605.07352.

[19]  G. Marcy,et al.  Prevalence of Earth-size Planets Orbiting Sun-like Stars , 2015, 1510.03902.

[20]  C. Dong,et al.  Atmospheric escape from the TRAPPIST-1 planets and implications for habitability , 2017, Proceedings of the National Academy of Sciences.

[21]  Updated Masses for the TRAPPIST-1 Planets , 2017, 1704.04290.

[22]  G. Piccioni,et al.  Sensitivity of net thermal flux to the abundance of trace gases in the lower atmosphere of Venus , 2016 .

[23]  F. Forget,et al.  Modeling climate diversity, tidal dynamics and the fate of volatiles on TRAPPIST-1 planets , 2017, 1707.06927.

[24]  Claudia Emde,et al.  New secondary-scattering correction in DISORT with increased efficiency for forward scattering , 2011 .

[25]  Aomawa L. Shields,et al.  The Habitability of Planets Orbiting M-dwarf Stars , 2016, 1610.05765.

[26]  C. McKay,et al.  The thermal structure of Titan's atmosphere. , 1989, Icarus.

[27]  T. Alberti,et al.  Comparative Climates of the Trappist-1 Planetary System: Results from a Simple Climate-vegetation Model , 2017, 1706.06005.

[28]  D. Hunten,et al.  The abundances of constituents of Titan's atmosphere from the GCMS instrument on the Huygens probe , 2005, Nature.

[29]  R. Freedman,et al.  Reliable infrared line lists for 13 CO2 isotopologues up to E′=18,000 cm−1 and 1500 K, with line shape parameters , 2014 .

[30]  D. Ehrenreich,et al.  Strong XUV irradiation of the Earth-sized exoplanets orbiting the ultracool dwarf TRAPPIST-1 , 2016, 1605.01564.

[32]  A. Borysow,et al.  Far infrared CIA spectra of N2-CH4 pairs for modeling of Titan's atmosphere , 1993 .

[33]  F. Fressin,et al.  CHARACTERISTICS OF KEPLER PLANETARY CANDIDATES BASED ON THE FIRST DATA SET , 2010, 1006.2799.

[34]  C. Clarke,et al.  Chemical enrichment of giant planets and discs due to pebble drift , 2017, 1705.03305.

[35]  Laurence S. Rothman,et al.  New section of the HITRAN database: Collision-induced absorption (CIA) , 2012 .

[36]  Kyle L. Luther,et al.  CHARACTERIZING TRANSITING EXOPLANET ATMOSPHERES WITH JWST , 2015, 1511.05528.

[37]  Edward W. Schwieterman,et al.  The Habitability of Proxima Centauri b: Environmental States and Observational Discriminants , 2016, Astrobiology.

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

[39]  Laura Kreidberg,et al.  PROSPECTS FOR CHARACTERIZING THE ATMOSPHERE OF PROXIMA CENTAURI b , 2016, 1608.07345.

[40]  B. Fegley,et al.  ATMOSPHERIC CHEMISTRY IN GIANT PLANETS, BROWN DWARFS, AND LOW-MASS DWARF STARS. III. IRON, MAGNESIUM, AND SILICON , 2010, 1001.3639.

[41]  Sergei N. Yurchenko,et al.  ExoMol line lists IV: The rotation-vibration spectrum of methane up to 1500 K , 2014, 1401.4852.

[42]  R. Yelle,et al.  Origin of oxygen species in Titan's atmosphere , 2008 .

[43]  Edwin A. Bergin,et al.  THE EFFECTS OF SNOWLINES ON C/O IN PLANETARY ATMOSPHERES , 2011, 1110.5567.

[44]  É. Bolmont,et al.  Water loss from terrestrial planets orbiting ultracool dwarfs: implications for the planets of TRAPPIST-1 , 2016, 1605.00616.

[45]  S. Hörst,et al.  Titan's atmosphere and climate , 2017 .

[46]  Mark Clampin,et al.  Transiting Exoplanet Survey Satellite (TESS) , 2014, Astronomical Telescopes and Instrumentation.

[47]  G. T. Fraser,et al.  Infrared Spectrum of the Continuum and Dimer Absorption in the Vicinity of the O2 Vibrational Fundamental in O2/CO2 Mixtures , 2004 .

[48]  Robin Wordsworth,et al.  ABIOTIC OXYGEN-DOMINATED ATMOSPHERES ON TERRESTRIAL HABITABLE ZONE PLANETS , 2014, 1403.2713.

[49]  David R. Alexander,et al.  The NEXTGEN Model Atmosphere Grid. II. Spherically Symmetric Model Atmospheres for Giant Stars with Effective Temperatures between 3000 and 6800 K , 1999, astro-ph/9907194.

[50]  David Crisp,et al.  The deep atmosphere of Venus revealed by high-resolution nightside spectra , 1990, Nature.

[51]  Khadeejah A. Zamudio,et al.  PLANETARY CANDIDATES OBSERVED BY KEPLER. VII. THE FIRST FULLY UNIFORM CATALOG BASED ON THE ENTIRE 48-MONTH DATA SET (Q1–Q17 DR24) , 2015, 1512.06149.

[52]  Drake Deming,et al.  Clouds in the atmosphere of the super-Earth exoplanet GJ 1214b , 2013, Nature.

[53]  S. Tashkun,et al.  Semi-empirical 12C16O2 IR line lists for simulations up to 1500 K and 20,000 cm−1 , 2013 .

[54]  A. Pál,et al.  Frequent Flaring in the TRAPPIST-1 System—Unsuited for Life? , 2017, 1703.10130.

[55]  A. Ingersoll.  The Runaway Greenhouse: A History of Water on Venus , 1969 .

[56]  Xavier Bonfils,et al.  A rocky planet transiting a nearby low-mass star , 2015, Nature.

[57]  Dimitar Sasselov,et al.  MASS–RADIUS RELATION FOR ROCKY PLANETS BASED ON PREM , 2015, 1512.08827.

[58]  Klaus Pontoppidan,et al.  PandExo: A Community Tool for Transiting Exoplanet Science with JWST & HST , 2017, 1702.01820.

[59]  Jonathan Fortney,et al.  Metal Enrichment Leads to Low Atmospheric C/O Ratios in Transiting Giant Exoplanets , 2016, 1611.08616.

[60]  M. D. Smith,et al.  The Modern Near-Surface Martian Climate: A Review of In-situ Meteorological Data from Viking to Curiosity , 2017 .

[61]  David P. Fleming,et al.  The Pale Green Dot: A Method to Characterize Proxima Centauri b Using Exo-Aurorae , 2016, 1609.09075.

[62]  Nikku Madhusudhan,et al.  NO THERMAL INVERSION AND A SOLAR WATER ABUNDANCE FOR THE HOT JUPITER HD 209458B FROM HST/WFC3 SPECTROSCOPY , 2016, 1605.08810.

[63]  P. Magain,et al.  Temperate Earth-sized planets transiting a nearby ultracool dwarf star , 2016, Nature.

[64]  Eric T. Wolf,et al.  Assessing the Habitability of the TRAPPIST-1 System Using a 3D Climate Model , 2017, 1703.05815.

[65]  Drake Deming,et al.  Spectral Resolution-linked Bias in Transit Spectroscopy of Extrasolar Planets , 2017, 1705.00625.

[66]  M. Marley,et al.  GASEOUS MEAN OPACITIES FOR GIANT PLANET AND ULTRACOOL DWARF ATMOSPHERES OVER A RANGE OF METALLICITIES AND TEMPERATURES , 2014, 1409.0026.

[67]  F. Mullally,et al.  The K2 Mission: Characterization and Early Results , 2014, 1402.5163.

[68]  Could we identify hot ocean-planets with CoRoT, Kepler and Doppler velocimetry? , 2007, astro-ph/0701608.

[69]  Ryan C. Terrien,et al.  HABITABLE ZONES AROUND MAIN-SEQUENCE STARS: NEW ESTIMATES , 2013, 1301.6674.

[70]  V. Eymet,et al.  Infrared collision-induced and far-line absorption in dense CO2 atmospheres , 2010 .

[71]  M. Line,et al.  A SYSTEMATIC RETRIEVAL ANALYSIS OF SECONDARY ECLIPSE SPECTRA. III. DIAGNOSING CHEMICAL DISEQUILIBRIUM IN PLANETARY ATMOSPHERES , 2013, 1309.6679.

[72]  T. Robinson.  A Theory of Exoplanet Transits with Light Scattering , 2017, 1701.05564.

[73]  Nikole K. Lewis,et al.  DISEQUILIBRIUM CARBON, OXYGEN, AND NITROGEN CHEMISTRY IN THE ATMOSPHERES OF HD 189733b AND HD 209458b , 2011, 1102.0063.

[74]  C. S. Fernandes,et al.  Seven temperate terrestrial planets around the nearby ultracool dwarf star TRAPPIST-1 , 2017, Nature.

[75]  James W. Head,et al.  The surface of Venus , 2003 .

[76]  T. Guillot,et al.  Atmospheric, Evolutionary, and Spectral Models of the Brown Dwarf Gliese 229 B , 1996, Science.

[77]  J. P. Dubois,et al.  A warm layer in Venus' cryosphere and high-altitude measurements of HF, HCl, H2O and HDO , 2007, Nature.

[78]  A. Borysow,et al.  Roto-Translational Collision-Induced Absorption of CO2for the Atmosphere of Venus at Frequencies from 0 to 250 cm−1, at Temperatures from 200 to 800 K , 1997 .

[79]  E. Dlugokencky,et al.  Global atmospheric methane: budget, changes and dangers , 2011, Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences.

[80]  K. Stamnes,et al.  Numerically stable algorithm for discrete-ordinate-method radiative transfer in multiple scattering and emitting layered media. , 1988, Applied optics.

[81]  G. Vasisht,et al.  THERMOCHEMICAL AND PHOTOCHEMICAL KINETICS IN COOLER HYDROGEN-DOMINATED EXTRASOLAR PLANETS: A METHANE-POOR GJ436b? , 2011, 1104.3183.

[82]  Kerri Cahoy,et al.  THERMAL EMISSION AND REFLECTED LIGHT SPECTRA OF SUPER EARTHS WITH FLAT TRANSMISSION SPECTRA , 2015, 1511.01492.