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Formation of habitable planets: Where does the water come from?

Event Details

Event Dates: 

Monday, February 25, 2013 - 9:00am

Speaker Name(s): 

Linda Elkins-Tanton

Speaker Affiliation(s): 

Carnegie Institution of Washington
Seminar Type/Subject

Event Details & Abstract: 

Planets obtain atmospheres, oceans, and interior volatiles during accretion. Accretion, however, changes character dramatically over the first hundred million years or so, changing from dust accretion, to relatively low-energy impacts of planetesimals, to high- energy impacts of embryos that produce magma oceans, finally tailing off of the size of impactors. The physics of each of these stages influences the quantity, composition, and phase of volatiles being delivered to the growing terrestrial planet, and therefore influences the quantity, composition, and final disposition of the volatiles in the planet.I will present a framework for thinking about these processes, with particular emphasis on the effects of early, interior magma oceans on planetesimals heated by aluminum 26, and on the effects of later surface magma oceans produced by impacts of embryos. A very small initial water content (less than a half mass percent) in the bulk magma ocean composition of the accreting Earth can produce a dense steam atmosphere, while a small change in chemistry can produce a carbon-based atmosphere, such as that on Venus. The low initial volatile contents required to degas a massive initial atmosphere that will collapse upon cooling into an ocean indicate that rocky super-Earth exoplanets may be expected to commonly produce water oceans within tens to hundreds of millions of years of their last major accretionary impact.