Biology
Scientific paper
Dec 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011agufm.p43c1697w&link_type=abstract
American Geophysical Union, Fall Meeting 2011, abstract #P43C-1697
Biology
[5220] Planetary Sciences: Astrobiology / Hydrothermal Systems And Weathering On Other Planets, [5416] Planetary Sciences: Solid Surface Planets / Glaciation, [6035] Planetary Sciences: Comets And Small Bodies / Orbital And Rotational Dynamics, [6296] Planetary Sciences: Solar System Objects / Extra-Solar Planets
Scientific paper
Water-rich terrestrial planets like the Earth are expected to be found in the extrasolar planetary systems in the near future. To discuss habitability of such planets, we have to investigate characteristic features of climate system of the water-rich terrestrial planets. One of the key factors which controls climate is 'obliquity', that is, the inclination of planet's axis. The climate of the Earth is stable partly because the Earth's obliquity is stabilized by the Moon, although it is not the case, in general, for other planets. Considering a large influence of obliquity on the solar energy distribution on the planetary surface, obliquity variations could induce large climate change on the planets. The climate of extraterrestrial planets with high obliquities was investigated by Williams and Kasting (1997). There are however few studies which systematically investigate the effects of obliquity change on the climate of the planets with carbonate-silicate geochemical cycle. In this study, we systematically investigate the climate of the water-rich terrestrial planets with a negative feedback mechanism of carbonate-silicate geochemical cycle under various obliquities and semi-major axes. We found that, while the "permanent ice-cap mode" (partially ice-covered throughout the year) and the "seasonal ice-cap mode" (partially ice-covered seasonally) exist stably at low obliquities, the ranges of semi-major axis for these climate modes shrink and finally disappear with an increase of obliquity. This is because latitudinal gradient of annual mean insolation becomes smaller with an increase of obliquity, resulting in meridional heat transport to be insufficient. We also found that the "ice-free mode" (no ice cap throughout the year) is paradoxically stable at outer part of habitable zone because of a decrease of meridional temperature gradient under very dense CO2 atmospheric condition. The "cyclic snowball mode" (a cycle of ice-covered state and ice-free state for a geological time scale) cannot appear at the CO2 degassing rate of present Earth, but appear widely at a 1/2 of the present degassing rate. When carbonate-silicate geochemical cycle is taken into account, the ranges of semi-major axis for all the climate modes expand at any obliquities, compared with the cases without carbon cycle, indicating that the carbon cycle strongly stabilizes the climate for the planets with any obliquities inside the habitable zone. Partial pressure of CO2 does not strongly depend on obliquity.
Kadoya S.
Tajika Eiichi
Watanabe Yu
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