Year: 2011
Type: article
Abstract: 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.
Authors: Raymond Pierrehumbert, Eric Gaidos
Institutions: University of Chicago, University of Hawaiʻi at Mānoa
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
SDG: Climate action
Open Access status: bronze
OpenAlex ID: W2096512653