Sagan-Ward Cyclical Climate Theory
  • Theory that Mars may sometimes be far less hostile to life than at present. The theory – a kind of martian version of Milankovitch cycles – depends upon the irregularity of the Martian orbit, which can sometimes allow the temperature at the poles of Mars to be higher than now, releasing water locked up there. The terraced appearance of the martian north polar cap, redolent of repeated freezing and thawing, is indirect evidence for this theory, as is the presence of large water-cut features on the surface of Mars. But the Sagan-Ward theory may not be enough to account for these features, since there now seems to be very little water available in the Martian polar caps even where they to melt.

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