The High Resolution Imaging Science 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“.
The HiRISE camera, orbiting the red planet on NASA’s Mars Reconnaissance Orbiter, is the most powerful camera ever to orbit another planet. It is operated at the University of Arizona in Tucson. HiRISE Principal Investigator Alfred McEwen of the UA’s Lunar and Planetary Laboratory and his team released the new image of the dark pit on Arsia Mons and several other stunning images yesterday on the HiRISE Website. New HiRISE images are released on the site every Wednesday.
Candidate Cavern Entrance Northeast of Arsia Mons

New View of Dark Pit on Arsia Mons

Pit Crater