Today's Mars photo is of a 'skylight,' or an opening to an underground cavern, located in a crater on the Pavonis Mons volcano. The opening is 35 meters (115 feet) in diameter. These types of underground caverns often form in volcanic regions where lava flows solidify near the surface, but continue flowing underneath (the resulting structure is commonly referred to as a lava tube). When the lava ceases flowing the caverns are left empty. In this particular instance the cavern has been determined to be approximately 20 meters (65 feet) deep.
|Image taken by the HiRISE camera on the Mars Reconnaissance Orbiter (Click Image for More Details)|