Other
Scientific paper
Sep 1997
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1997icar..129..254w&link_type=abstract
Icarus, Volume 129, Issue 1, pp. 254-267.
Other
40
Scientific paper
Earth's obliquity would vary chaotically from 0 deg to 85 deg were it not for the presence of the Moon (J. Laskar, F. Joutel, and P. Robutel, 1993, Nature 361, 615-617). The Moon itself is thought to be an accident of accretion, formed by a glancing blow from a Mars-sized planetesimal. Hence, planets with similar moons and stable obliquities may be extremely rare. This has lead Laskar and colleagues to suggest that the number of Earth-like planets with high obliquities and temperate, life-supporting climates may be small. To test this proposition, we have used an energy-balance climate model to simulate Earth's climate at obliquities up to 90 deg. We show that Earth's climate would become regionally severe in such circumstances, with large seasonal cycles and accompanying temperature extremes on middle- and high-latitude continents which might be damaging to many forms of life. The response of other, hypothetical, Earth-like planets to large obliquity fluctuations depends on their land-sea distribution and on their position within the habitable zone (HZ) around their star. Planets with several modest-sized continents or equatorial super-continents are more climatically stable than those with polar super-continents. Planets farther out in the HZ are less affected by high obliquities because their atmospheres should accumulate CO_2 in response to the carbonate-silicate cycle. Dense, CO_2-rich atmospheres transport heat very effectively and therefore lim! it the magnitude of both seasonal cycles and latitudinal temperature gradients. We conclude that a significant fraction of extrasolar Earth-like planets may still be habitable, even if they are subject to large obliquity fluctuations.
Kasting James F.
Williams Darren M.
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