Nebular ingassing as a source of volatiles to the Terrestrial planets

Date & time

1–2pm 23 May 2018


Jaeger 1 Seminar Room, RSES


Zachary Sharp (University of New Mexico), The Mineralogical Society of America 2018 Distinguished Lecturer

Event series


 Adele Morrison

Please note, this special school seminar is on a Wednesday.

The source of volatiles is critical for understanding Terrestrial planet formation and the conditions that lead to habitable planets. The Earth lies inside the so-called 'snow line', outside of which H2O condenses to ice and can be incorporated into growing planetary bodies. Inside the snow line, incorporation of volatile elements is more problematic. A number of ideas have been proposed to explain sourcing of volatiles. We consider the idea that ingassing of a nebular atmosphere was an important source of hydrogen and 3He to Earth. If the proto-solar nebula was still present by the time the Earth approached its present size, then a dense atmosphere would necessarily develop and ingassing would be inevitable.

 Hydrogen ingassing is a two-step process. The first stage involves the formation of a dense nebular atmosphere in the first ~10 My after the collapse of the proto-solar nebula. The atmosphere would cause heating of the planetary core to sufficient temperatures to cause complete melting. Massive ingassing of H2, H2O and He would occur. The second stage occurs after the nebula dissipates. Over time, volatiles would degas into the thin atmosphere and be lost to space by hydrodynamic escape. The degassing of H2 is an extremely effective oxidation mechanism, and explains the high present-day f(O2) of Earth’s mantle. Evidence for the low D/H ratio of nebular hydrogen is preserved in primitive picritic laves from Baffin Islands. The scenario outlined here eliminates many of the problems inherent in previous models for volatile delivery to Earth.

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