NANTES, FRANCE—Despite basking in the sun's fiery glow, tiny Mercury, the innermost planet in our solar system, is probably home to extensive ice fields. Twenty years ago, radar observations from Earth revealed small, highly reflective areas close to Mercury's poles, suggesting the presence of ice. Now, NASA's MESSENGER spacecraft, which has orbited Mercury since March, has confirmed that these radar-bright patches neatly coincide with deep crater floors near the poles that never receive any sunlight at all. This new color-coded photo mosaic of Mercury's south polar region, presented here today at a joint meeting of the European Planetary Science Congress and the Division for Planetary Sciences of the American Astronomical Society, shows these "freezer" areas as dark blotches. According to MESSENGER instrument scientist Nancy Chabot of the Johns Hopkins University's Applied Physics Laboratory in Laurel, Maryland, a full one-fifth of the region within 200 kilometers of Mercury's south pole is in permanent shadow. "It's all consistent with there being water ice," she says.
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