The evidence for abundant liquid water on early Mars despite the faint young Sun is a long-standing problem in planetary research. Here we present new ab initio spectroscopic and line-by-line climate calculations of the warming potential of reduced atmospheres on early Mars. We show that the strength of both CO2-H2 and CO2-CH4 collision-induced absorption (CIA) has previously been significantly underestimated. Contrary to previous expectations, methane could have acted as a powerful greenhouse gas on early Mars due to CO2-CH4 CIA in the critical 250-500 cm^-1 spectral window region. In atmospheres of 0.5 bar CO2 or more, percent levels of H2 or CH4 raise annual mean surface temperatures by tens of degrees, with temperatures reaching 273 K for pressures of 1.25-2~bar and 2-10% of H2 and CH4. Methane and hydrogen produced following aqueous alteration of Mars' crust could have combined with volcanically outgassed CO2 to form transient atmospheres of this composition 4.5-3.5 Ga. Our results also suggest that inhabited exoplanets could retain surface liquid water at significant distances from their host stars.
@article{arxiv.1610.09697,
title = {Transient reducing greenhouse warming on early Mars},
author = {Robin Wordsworth and Yulia Kalugina and Sergei Lokshtanov and Andrei Vigasin and Bethany Ehlmann and James Head and Cecilia Sanders and Huize Wang},
journal= {arXiv preprint arXiv:1610.09697},
year = {2017}
}
Comments
published in GRL Jan 2017, this is final preprint version