Ice World Beyond Earth—Brief Introduction to Planetary Cryosphere postprint

Abstract: In the present paper, we briefly introduce the planetary cryosphere of solar planets and exoplanets. Planets and satellites in the solar system have very different surface temperatures. Therefore, they have very different cryosphere. Mercury and the Moon likely have water ice in the permanent dark areas of craters in polar regions. Venus is too hot to have a cryosphere. Mars has permanent polar ice caps that include both water ice and carbon-dioxide dry ice. Beyond the snowline of the solar system, there are many dwarf planets and satellites that are mainly consisted of water ice. With extremely low temperatures, water ice becomes even harder than the rocks on Earth and is actually the shell layer of these satellites and dwarf planets. In addition to water ice, other gases over Earth, such as CO2, CH4, N2, CO, and so on, are condensed to solid states under conditions of extremely low temperatures. They form different cryosphere from water ice. Therefore, planetary cryosphere is very different from that on Earth, and they have plenty divergences. Studies on planetary cryosphere would largely broaden our understanding on Earth’s cryosphere and benefit our understanding of the formation of the solar system, origin of water on Earth, evolution of life and climate environment on Earth, and extra-solar life detection in future.