• DOI:10.1088/2041-8205/734/1/L13
• Corpus ID: 7404376

HYDROGEN GREENHOUSE PLANETS BEYOND THE HABITABLE ZONE

@article{Pierrehumbert2011HYDROGENGP,
  title={HYDROGEN GREENHOUSE PLANETS BEYOND THE HABITABLE ZONE},
  author={Raymond T. Pierrehumbert and Eric Gaidos},
  journal={The Astrophysical Journal},
  year={2011},
  volume={734}
}

• R. Pierrehumbert, E. Gaidos
• Published 29 April 2011
• Physics, Geology
• The Astrophysical Journal

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 H2–He mixtures can maintain surface temperatures above the freezing point of water well beyond the “classical” habitable zone defined for CO2 greenhouse atmospheres. Using a onedimensional radiative–convective model, we find that 40 bars of pure H2 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 H2, 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 H2–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 H2–He atmosphere and be habitable at ∼2.6 AU from its host M star.