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Project Progress

Steve Desch and postdoc Melissa Morris (ASU) presented and analyzed an idea that ²⁶Al may control volatile delivery to solar and extrasolar terrestrial planets, especially water. That’s because ²⁶Al severely heats asteroids and may have caused their devolatilization. If so, having earths as dry as our Earth would be rare, because Earth could have gotten most of its water from asteroids. However, ²⁶Al should be rare in other solar systems, so “earths” in those other solar systems would have accreted much more water. Steve Desch synthesized evidence from impact modeling and chlorine geochemistry on Earth and argued that the planet is even drier than when it formed, due to the moon-forming impact. Therefore, other extrasolar “earths” may be much wetter than our Earth. In a related effort, Ariel Anbar and Desch began to develop the idea that on planets with much more water than the Earth (e.g., > 50 oceans’ worth; super-Earths), the base of the ocean would be water Ice VI or Ice VII and would cut off chemical communication with the mantle, with unfortunate consequences for habitability.

Elemental mass balance calculations have been performed to evaluate amounts of water in extrasolar planetary systems based on composition of parent stars detected with spectroscopy methods. It is shown that water-bearing solid extrasolar planets (including super-Earths) should have host stars with low carbon/oxygen and metals/oxygen ratios. The work was performed by Zolotov. Elemental mass balance calculations have been used to evaluate composition of C-H-O-N volatiles condensed around stars with known composition. The developed algorithm has been tested on solar system materials though evaluation of bulk composition of comets. Results show a promising match with independent observations of solar system materials (e.g., interplanetary dust particles). It follows that the same algorithm could be used for other stars with known composition. This work was performed by Graduate Student Lev Spivak-Birndorf, working with Zolotov. The results have been reported at the Meteoritical Society meeting in 2010.