Thursday, July 18, 2013

M Dwarves Might Have Water Trapped Terrestrial Worlds

Water Trapped Worlds


1. Kristen Menou (a)


a. Department of Astronomy, Columbia University, 550 West 120th Street, New York, NY 10027


Although tidally-locked habitable planets orbiting nearby M-dwarf stars are among the best astronomical targets to search for extrasolar life, they may also be de cient in volatiles and water. Climate models for this class of planets show atmospheric transport of water from the dayside to the nightside, where it is precipitated as snow and trapped as ice. Since ice only slowly ows back to the dayside upon accumulation, the resulting hydrological cycle can trap a large amount of water in the form of nightside ice. Using ice sheet dynamical and thermodynamical constraints, I illustrate how planets with less than about a quarter the Earth's oceans could trap most of their surface water on the nightside. This would leave their dayside, where habitable conditions are met, potentially dry. The amount and distribution of residual liquid water on the dayside depend on a variety of geophysical factors, including the e ciency of rock weathering at regulating atmospheric CO2 as dayside ocean basins dry-up. Water-trapped worlds with dry daysides may o er similar advantages as land planets for habitability, by contrast with worlds where more abundant water freely flows around the globe.

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