Planetary Evolution From High Orbit
New gullies that did not exist three years ago have appeared on
a Martian sand dune.That's just one of the surprising discoveries
that have resulted from the extended life of NASA's Mars Global
Surveyor, which this month began its ninth year in orbit around
Mars. Boulders tumbling down a Martian slope left tracks that
weren't there two years ago. New impact craters formed since the
1970s suggest changes to age-estimating models. And for three Mars
summers in a row, deposits of frozen carbon dioxide near Mars'
south pole have shrunk from the previous year's size, suggesting a
climate change in progress.
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