Protostars and Planets VI, Heidelberg, July 15-20, 2013
THE STRUCTURES OF SURFACE H2O LAYERS OF ICE-COVERED PLANETS WITH HIGH-PRESSURE ICE
Ueta, Shoji (Earth and Planetary Sciences, Tokyo Institute of Technology)
Sasaki, Takanori (Earth and Planetary Sciences, Tokyo Institute of Technology)
Many extrasolar (bound) terrestrial planets and free-floating (unbound) planets have been discovered. The existence of bound and unbound terrestrial planets which have liquid water is an important question, especially in terms of habitability. Even for a globally ice-covered planet, geothermal heat flow from the planetary interior is thought to melt the interior ice so that an internal ocean covered with an ice shell can exist. In this paper, we discuss the conditions for terrestrial planets to have an internal ocean on the timescale of planetary evolution in terms of the planetary mass, distance from the central star, water abundance, and abundance of radiogenic heat sources. In addition, we investigate the structures of surface H2O layers of ice-covered planets with considering effects of ice under high pressure (high-pressure ice). At 1AU, 1 Earthfs mass planet with 0.6-25 times H2O mass of the Earth could have an internal ocean. However, high-pressure ice layers could appear between the internal ocean and the rock-part on the planet with an H2O mass > 25 times Earthfs H2O mass. The planetary mass and water abundance on the surface strongly constrain the conditions for an extrasolar terrestrial planet to have an internal ocean and not to hold high-pressure ice under the internal ocean. The appearance of the structure with high-pressure ice layers might affect the habitability of the planet.
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