2011/04/29 by Raymond T. Pierrehumbert, Raymond Pierrehumbert, Eric Gaidos · 11 citations
Chemistry · Physics and Astronomy · #Anoxygenic photosynthesis #Astro and Planetary Science #Astrobiology #Astronomy #Astrophysics #Astrophysics and Star Formation Studies #Atmosphere (unit) #Chemistry #Circumstellar habitable zone #Exoplanet #Kepler-69c #Meteorology #Photosynthesis #Phototroph #Physics #Planet #Stars #Stellar, planetary, and galactic studies #Terrestrial planet #astro-ph.EP
paper · pdf · doi:10.1088/2041-8205/734/1/l13
Accepted to Astrophysical Journal Letters
arxiv created 2011/04/29 · openalex publication_date 2011/05/19 · arxiv updated 2015/05/28 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/05
We show that collision-induced absorption allows molecular hydrogen to act as an incondensible greenhouse gas and that bars or tens of bars of primordial H 2 –He mixtures can maintain surface temperatures above the freezing point of water well beyond the "classical" habitable zone defined for CO 2 greenhouse atmospheres. Using a one-dimensional radiative–convective model, we find that 40 bars of pure H 2 on a three Earth-mass planet can maintain a surface temperature of 280 K out to 1.5 AU from an early-type M dwarf star and 10 AU from a G-type star. Neglecting the effects of clouds and of gaseous absorbers besides H 2 , the flux at the surface would be sufficient for photosynthesis by cyanobacteria (in the G star case) or anoxygenic phototrophs (in the M star case). We argue that primordial atmospheres of one to several hundred bars of H 2 –He are possible and use a model of hydrogen escape to show that such atmospheres are likely to persist further than 1.5 AU from M stars, and 2 AU from G stars, assuming these planets have protecting magnetic fields. We predict that the microlensing planet OGLE-05-390Lb could have retained an H 2 –He atmosphere and be habitable at ∼2.6 AU from its host M star.