NASA's Mars Global Surveyor and Mars Odyssey missions have provided evidence of a recent ice age on Mars. In contrast to Earth's ice ages, a martian ice age waxes when the poles warm up and water vapor is transported toward lower latitudes. Martian ice ages wane when the poles cool and lock water into polar icecaps. The "pacemakers" of ice ages on Mars appear to be much more extreme than the comparable drivers of climate change on Earth. Variations in the planet's orbit and tilt produce remarkable changes in the distribution of water ice from polar regions down to latitudes equivalent to Houston or Egypt. Researchers, using NASA spacecraft data and analogies to Earth's Antarctic Dry Valleys, report their findings in the Thursday, Dec. 18 edition of the journal Nature. "Of all the solar system planets, Mars has the climate most like that of Earth. Both are sensitive to small changes in orbital parameters," said planetary scientist Dr. James Head of Brown University, Providence, R.I., lead author of the study. "Now we're seeing that Mars, like Earth, is in a period between ice ages."

Discoveries on Mars, since 1999, of relatively recent water- carved gullies, glacier-like flows, regional buried ice and possible snow packs created excitement among scientists who study Earth and other planets. Information from the Mars Global Surveyor and Odyssey missions provided more evidence of an icy recent past.

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