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Watching Seasons Pass on Mars
Just as migrating birds herald the changing seasons on Earth, sand dunes show seasonal change on the fourth rock from the Sun. From a distance, crescent-shaped dunes near the north pole of Mars can even resemble birds in flight.
The dunes are part of a sea of sand that scientists call an "erg." Summer is the time of year when their winter coat of ice evaporates and exposes the reddish-brown material underneath. Like birds flying in front of the moon on Earth, meter-thick waves of frost on Mars vanish and reappear depending on the season.
Thermal Emission Imaging System, 2001 Mars Odyssey
Credit: NASA/JPL-Caltech/Arizona State University
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