Impact Delivery of Reduced Greenhouse Gases on Early Mars
Abstract
Reducing greenhouse gases are the latest trend in finding solutions to the early Mars climate dilemma. In thick CO2 atmospheres with modest concentrations of H2 and/or CH4, collision induced absorptions can reduce the outgoing long wave radiation enough to provide a significant greenhouse effect. To raise surface temperatures significantly by this process, surface pressures must be at least 500 mb and H2 and/or CH4 concentrations must be at or above the several percent level. Volcanism, serpentinization, and impacts are possible sources for reduced gases. Here we investigate the delivery of such gases by impact degassing from comets and asteroids. We use a time-marching stochastic impactor model that reproduces the observed crater size frequency distribution of Noachian surfaces. Following each impact, reduced gases are added to the atmosphere from a production function based on gas equilibrium calculations for several classes of meteorites and comets at typical post-impact temperatures. Escape and photochemistry then remove the reduced greenhouse gases continuously in time throughout each simulation. We then conduct an ensemble of simulations with this simple model varying the surface pressure, impact history, reduced gas production and escape functions, and mix of impactor types, to determine if this could be a potentially important part of the early Mars story. Our goal is to determine the duration of impact events that elevate reduced gas concentrations to significant levels and the total time of such events throughout the Noachian. Our initial simulations indicate that large impactors can raise H2 concentrations above the 10% level - a level high enough for a very strong greenhouse effect in a 1 bar CO2 atmosphere - for millions of years, and that the total time spent at or above that level can be in the 10's of millions of years range. These are interesting results that we plan to explore more thoroughly for the meeting.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2017
- Bibcode:
- 2017AGUFM.P33C2897H
- Keywords:
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- 5405 Atmospheres;
- PLANETARY SCIENCES: SOLID SURFACE PLANETS;
- 5415 Erosion and weathering;
- PLANETARY SCIENCES: SOLID SURFACE PLANETS;
- 5416 Glaciation;
- PLANETARY SCIENCES: SOLID SURFACE PLANETS;
- 5419 Hydrology and fluvial processes;
- PLANETARY SCIENCES: SOLID SURFACE PLANETS