Martian Permafrost

The view from a satellite circling some parts of Mars is much the same as that from a light aircraft flying over parts of Alaska. Polygonal soil and the slumping features caused by repeated freezing and thawing of the melting of ground ice are seen many places in Alaska. Two U. S. Geological Survey scientists, Michael H. Carr and Gerald G. Schaber, suggest that similar features on Mars indicate the existence of permafrost there, too.

On a hot Martian summer day, the temperature at low latitudes does rise above freezing at midday. However, the average (mean annual) temperature everywhere on Mars is well below freezing. At latitudes higher than 40 degrees on Mars (which would be about the same latitude as northern California), ice in the soil is thought to be able to exist permanently under present conditions.

Photographs of patterned (polygonal shapes) ground on Mars do look remarkably like those from Alaska. There is one major difference: the Martian polygons are up to 20 kilometers across and thus are 200 times bigger than the largest Alaskan polygons, which rarely exceed 100 meters.

These and other differences make it impossible to be absolutely certain that the patterned ground and chaotic terrain observed on Mars actually is caused by permafrost. Contraction of cooling materials such as lavas can produce similar features. Nevertheless, conditions on Mars are so favorable to the formation and retention of permafrost that it is almost certain to exist there.