TY - JOUR
T1 - Testing the early Mars H2-CO2 greenhouse hypothesis with a 1-D photochemical model
AU - Batalha, Natasha
AU - Domagal-Goldman, Shawn D.
AU - Ramirez, Ramses
AU - Kasting, James F.
N1 - Funding Information:
This material is based upon work supported by the National Science Foundation under Grant No. DGE1255832 to N. Batalha. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation. JFK acknowledges support from NASA’s Exobiology and Astrobiology programs . R.R. acknowledges support from the Simon’s Foundation (SCOL 290357, L.K.) and the Carl Sagan Institute .
Publisher Copyright:
© 2015 Elsevier Inc.
PY - 2015/9/5
Y1 - 2015/9/5
N2 - A recent study by Ramirez et al. (Ramirez, R.M. et al. [2014]. Nat. Geosci. 7(1), 59-63. (accessed 16.09.14)) demonstrated that an atmosphere with 1.3-4bar of CO2 and H2O, in addition to 5-20% H2, could have raised the mean annual and global surface temperature of early Mars above the freezing point of water. Such warm temperatures appear necessary to generate the rainfall (or snowfall) amounts required to carve the ancient martian valleys. Here, we use our best estimates for early martian outgassing rates, along with a 1-D photochemical model, to assess the conversion efficiency of CO, CH4, and H2S to CO2, SO2, and H2. Our outgassing estimates assume that Mars was actively recycling volatiles between its crust and interior, as Earth does today. H2 production from serpentinization and deposition of banded iron-formations is also considered. Under these assumptions, maintaining an H2 concentration of ~1-2% by volume is achievable, but reaching 5% H2 requires additional H2 sources or a slowing of the hydrogen escape rate below the diffusion limit. If the early martian atmosphere was indeed H2-rich, we might be able to see evidence of this in the rock record. The hypothesis proposed here is consistent with new data from the Curiosity Rover, which show evidence for a long-lived lake in Gale Crater near Mt. Sharp. It is also consistent with measured oxygen fugacities of martian meteorites, which show evidence for progressive mantle oxidation over time.
AB - A recent study by Ramirez et al. (Ramirez, R.M. et al. [2014]. Nat. Geosci. 7(1), 59-63. (accessed 16.09.14)) demonstrated that an atmosphere with 1.3-4bar of CO2 and H2O, in addition to 5-20% H2, could have raised the mean annual and global surface temperature of early Mars above the freezing point of water. Such warm temperatures appear necessary to generate the rainfall (or snowfall) amounts required to carve the ancient martian valleys. Here, we use our best estimates for early martian outgassing rates, along with a 1-D photochemical model, to assess the conversion efficiency of CO, CH4, and H2S to CO2, SO2, and H2. Our outgassing estimates assume that Mars was actively recycling volatiles between its crust and interior, as Earth does today. H2 production from serpentinization and deposition of banded iron-formations is also considered. Under these assumptions, maintaining an H2 concentration of ~1-2% by volume is achievable, but reaching 5% H2 requires additional H2 sources or a slowing of the hydrogen escape rate below the diffusion limit. If the early martian atmosphere was indeed H2-rich, we might be able to see evidence of this in the rock record. The hypothesis proposed here is consistent with new data from the Curiosity Rover, which show evidence for a long-lived lake in Gale Crater near Mt. Sharp. It is also consistent with measured oxygen fugacities of martian meteorites, which show evidence for progressive mantle oxidation over time.
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U2 - 10.1016/j.icarus.2015.06.016
DO - 10.1016/j.icarus.2015.06.016
M3 - Article
AN - SCOPUS:84935521518
SN - 0019-1035
VL - 258
SP - 337
EP - 349
JO - Icarus
JF - Icarus
ER -