Studying Habitability in Ancient Martian Environments

This set of images shows the results from the rock abrasion tool from NASA's Mars Exploration Rover Opportunity (left) and the drill from NASA's Curiosity rover (right). Note how the rock grindings from Opportunity are brownish red, indicating the presence of hematite, a strongly oxidized iron-bearing mineral. Such minerals are less supportive of habitability and also may degrade organic compounds. The diameter of the abraded circle is 1.8 inches (4.5 centimeters).
On the right is the hole produced by Curiosity during the first drilling into a rock on Mars to collect a sample from inside the rock. In this case, the rock produced gray tailings -- not red -- suggesting the presence of iron that is less oxidized. One possibility is magnetite, which was determined to be present by Curiosity's Chemistry and Mineralogy instrument. Magnetite has less oxygen than hematite and would be more compatible with habitability and the preservation of organics, all other factors being equal.

See http://photojournal.jpl.nasa.gov/catalog/PIA16834