Where Mars isn't red
Feb 8, 2010
In an impact crater inside a volcanic crater high on a Martian mountaintop, ancient bedrock is exposed. The high elevation and crater ramparts keep out the red dust that swirls over most of the planet. This picture of the rocks there was captured by infrared sensors in an orbiting telescope, part of a NASA probe known as HiRISE.
The rocks are more than 3 billion years old, among the oldest known on the planet. The infrared sensors detected a variety of hydrated minerals, evidence that this place was once under water, for a long time. Some of the minerals detected contain chloride, as in table salt.
There is still H2O on Mars--pictures taken early in the morning often show frost--but the Martian atmosphere is so thin nowadays that water is unstable in its liquid form.