Four days after scientists announced that rocks examined by the rover Opportunity in Meridiani Planum were once soaked with water, Opportunity’s twin Spirit made some headline news of its own. In a press conference this morning at the Jet Propulsion laboratory in Pasadena, Dr. Ray Arvidson, Deputy Principal Investigator for the rovers, announced that Spirit had discovered the telltale signs that some amount water had once been present in Gusev Crater as well.
Spirit made its discovery while studying a 60-centimeter (23 inch) high volcanic rock nicknamed “Humphrey,” in a region that scientists refer to as the “middle ground”. Spirit first drilled into Humphrey with its rock abrasion tool (RAT), creating a circular depression in the rock where the external layer had been removed. The rover then examined the area closely with its microscopic imager.
What the rover saw, and transmitted back to Earth, was a series of fractures in the rock, filled with minerals. Geologists are familiar with similar formations on Earth, where it is considered a sure sign of water deposits. Unlike Opportunity’s discovery in Meridiani Planum, which points to large amounts of water soaking the rocks, Spirit’s discovery suggest the presence of minute amounts of water. Most likely, according to Arvidson, the water was mixed in with the Martian magma that created Humphrey billions of years ago. As the magma cooled and formed the rock, the water separated from it, creating the cracks and mineral deposits.
The discoveries of Opportunity and Spirit over the past week point to very different geological histories at the respective landing sites of the two rover. Nevertheless, the discovery of signs of water by both rovers, on opposite sides of the planet, suggests that water had an important and active role in shaping the Martian landscape at some point in the past.