Images taken by the Mars Global Surveyor, now orbiting the Red Planet, suggest that most areas with geological features known as patterned ground appear at high latitudes, the same regions where large quantities of ice may lie just under the planet's surface.
At hundreds of Martian sites, the landscape is covered with mosaics of polygons, each of which measures between 30 and 200 meters across. Some areas of patterned ground are heavily cratered or eroded, which probably indicates their great age. Most large areas of more-intact patterned ground are located at latitudes above 55°, says William C. Feldman of the Los Alamos (N.M.) National Laboratory. That pattern hints that climate played a role in the features' formation, Feldman and his colleagues contend in the Aug. 25 Journal of Geophysical Research (Planets).
On Earth, patterned ground is formed by cycles of freezing and thawing in water-soaked soil or by the repeated expansion and contraction of subter