37th DPS Meeting, 4-9 September 2005
Session 31 Extrasolar Planets
Poster, Tuesday, September 6, 2005, 6:00-7:15pm, Music Recital Room

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[31.06] Constraints on the Mass of Planets with Water of Nebular Origin

M. Ikoma, H. Genda (Tokyo Tech)

Detection of many extrasolar planets has stimulated us to make a systematic study of planet formation. Theoretical studies on the accretion and dynamical evolution of planets have constrained the masses and periods of planets in extrasolar systems. From an astrobiological point of view, special attention has been paid to probabilities of the existence of planets in the habitable zone where a planet can keep liquid water above its surface. Few studies have, however, discussed how likely a planet acquires a sufficient amount of water. Although there are several sources of water on terrestrial planets, we focus on an idea that water is produced on a planet by oxidation of a hydrogen-rich atmosphere, the nebular gas being attracted gravitationally by the planet. The process of water production could work if a planet captures a sufficient amount of hydrogen, has a molten surface (i.e., magma oceans), and contains some oxide. Our extensive investigation of properties of the hydrogen-rich atmosphere shows the former two conditions are fulfilled on an Earth-size planet for a wide range of parameters. Moreover, some oxide such as FeO is common material in planets, as long as the C/O ratio of extrasolar systems is less than unity. Therefore, sufficient water on an Earth-sized rocky planet is a natural consequence of planet formation. The range of masses of those potentially-habitable planets is also constrained.

This research was supported by the 21st Century COE Program ``How to build habitable planets", Tokyo Institute of Technology, sponsored by the Ministry of Education, Culture, Sports, Technology and Science (MEXT), Japan.

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Bulletin of the American Astronomical Society, 37 #3
© 2004. The American Astronomical Soceity.