The High Resolution Imaging Experiment (HiRISE) has confirmed that a dark pit seen on Mars in an earlier HiRISE image really is a vertical shaft that cuts through lava flow on the flank of the Arsia Mons volcano. Such pits form on similar volcanoes in Hawaii and are called "pit craters."
More: LPL - HiRISE access images, news, and and instrument information
Two months after sky-darkening dust from severe storms nearly killed NASA's Mars exploration rovers, the solar powered robots are awake and ready to continue their mission. Opportunity's planned descent into the giant Victoria Crater was delayed, but now the rover is preparing to drive into the 800-meter-diameter crater (half-mile-diameter) as early as Sept. 11. Victoria Crater contains an exposed layer of bright rocks that may preserve evidence of interaction between the Martian atmosphere and surface from millions of years ago, when the atmosphere might have been different from today's. Victoria is the biggest crater Opportunity has visited.
Spirit, Opportunity's rover twin, also survived the global dust storms. The rovers are 43 months into missions originally planned to last three months. On Sept. 5, Spirit climbed onto its long-term destination called Home Plate, a plateau of layered bedrock bearing clues to an explosive mixture of lava and water.