1 March 2012
1 March 2012
Speaker: Raymond Pierrehumbert (U. of Chicago)
Title:Atmospheric Evolution on Water-Worlds
Abstract:The classic water-loss scenario for (typically hot) planets with high water vapor content in the upper atmosphere consists of FUV-driven photolysis followed by hydrogen escape. However, this generally assumes a sink for the oxygen produced by photolysis. Typically, the oxygen sink is assumed to be due to oxidation of iron minerals in the crust. On a planet like GJ1214b without a substantial rocky surface, or any planet with a deep enough ocean or weak enough tectonic resurfacing that reaction with crustal minerals is inhibited, this sink could be inactive. I examine the likely evolution pathways if oxygen is allowed to accumulate in the atmosphere, and find that the loss of more than a few percent of the initial ocean leads to efficient re-formation of water, driving hydrogen to low concentrations and inhibiting escape. Such inhibition may be particularly important in helping Super-Earths orbiting M-stars to retain their oceans through the prolonged active stages of such stars.
I shall touch on a few additional topics concerning evolution of water-rich planets, including the importance of silicate weathering (or lack of substantial CO2 outgassing) in eliminating the cold-trap for water vapor, the implications of strong NIR heating of the upper atmosphere in the case of M-star insolation, and interpretation of transit-depth observations of GJ1214b.
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