no shortage of frozen water at mars’s poles

Both of Mars’s polar ice caps consist mostly of frozen water, report Shane Byrne and Andrew Ingersoll of the California Institute of Technology in last week’s Science. It was long thought that the southern ice cap was made almost entirely of frozen carbon dioxide, or dry ice, unlike its northern cap, which was made almost entirely of frozen water and had only a thin crust of dry ice. But recent thermal and high-resolution images made by NASA’s Mars Odyssey and Mars Global Surveyor spacecrafts show that the southern polar cap is too warm to be made entirely of dry ice, which evaporates at a higher temperature than the freezing point of water. According to the new study, both ice caps are fairly similar except that the south pole’s dry ice crust is slightly thicker than the north’s. The new mystery is, where is all the carbon dioxide? If Mars was ever warm and wet — and its landscape of flood and riverlike channels make it seem probable — it would require large amounts of carbon dioxide to provide a greenhouse effect so that liquid water could have existed.

This news brief appeared in the Random Data column of the Boston Globe’s Health/Science section on 2/18/2003.
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