Warming early Mars with CO2 and H2

Abstract

The presence of valleys on ancient terrains of Mars suggest that liquid water flowed on the martian surface 3.8 billion years ago or before. The above-freezing temperatures required to explain valley formation could have been transient, in response to frequent large meteorite impacts on early Mars, or they could have been caused by long-lived greenhouse warming. Climate models that consider only the greenhouse gases carbon dioxide and water vapor have been unable to recreate warm surface conditions, given the lower solar luminosity at that time. Here we use a one-dimensional climate model to demonstrate that an atmosphere containing 1.3-4 bar of CO2 and water vapor, along with 5 to 20 percent H2, could have raised the mean surface temperature of early Mars above the freezing point of water. Vigorous volcanic outgassing from a highly reduced early martian mantle is expected to provide sufficient atmospheric H2 and CO2, the latter from the photochemical oxidation of outgassed CH4 and CO, to form a CO2-H2 greenhouse. Such a dense early martian atmosphere is consistent with independent estimates of surface pressure based on cratering data.Comment: 48 pages, 12 figures, and 4 tables. The official Nature Geoscience version is found here: http://www.nature.com/ngeo/journal/v7/n1/full/ngeo2000.htm

Carbon monoxide as a metabolic energy source for extremely halophilic microbes: Implications for microbial activity in Mars regolith

“…If extremely halophilic CO oxidizers exist on contemporary Mars, they could use multiple electron acceptors, including molecular oxygen. Any such microbes might represent relicts from earlier periods in Mars' history when atmospheric CO concentrations could have been much higher than at present (69,70). The plausibility of microbial CO oxidation on Mars also suggests that extremely halophilic CO oxidizers as well as other CO-oxidizing microbes might be exploited in efforts to manipulate Mars' atmosphere and to establish multifunctional microbial communities in the regolith or in engineered environments.…”

Paleohydrology of Eberswalde crater, Mars

“…This discrepancy between empirical and theoretical results has motivated investigations of higher-thanexpected solar luminosity, obliquity variations, more effective greenhouse gases, carbon dioxide clouds, albedo differences, and release of volatiles by impacts or volcanism as possible ways of warming the planet (e.g., Baker et al, 1991;Whitmire et al, 1995;Sagan and Chyba, 1997;Segura et al, 2002;Colaprete and Toon, 2003;Segura et al, 2008Segura et al, , 2012Mischna et al, 2013;Ramirez et al, 2014). Other investigators have examined ways to erode valleys under cold conditions, including ice flow, stream flow under an ice cover, or generation of meltwater by surface (impact ejecta) or subsurface (geothermal) heat sources (e.g., Wallace and Sagan, 1979;Carr, 1983;Brakenridge et al, 1985;Wilhelms and Baldwin, 1989;Brakenridge, 1990;Gulick and Baker, 1990;Carr, 1995;Goldspiel and Squyres, 2000;Harrison and Grimm, 2002;Carr and Head, 2003;Mangold et al, 2012a).…”

The physics of Martian weather and climate: a review

“…Suggested species have included NH 3 , SO 2 , CH 4 , H 2 S, H 2 O, organic hazes and even molecular H 2 itself (e.g. see Johnson et al 2008, Mischna et al 2013, Ramirez et al 2013, Sagan and Mullen 1972. Sulphur compounds have received quite a lot of attention (see Johnson et al 2008, Mischna et al 2013, for more discussion), since they can provide opacity in regions of the infrared spectrum that complements that due to CO 2 and H 2 O.…”