Aug. 30, 2011 - On the slopes of the vast Martian shield volcano Pavonis Mons, a rather odd-looking crater resides. Originally spotted by NASA's Mars Reconnaissance Orbiter (MRO) Context Camera (CTX) earlier this year, mission managers decided to zoom in on the suspect feature using the awesome power of the MRO's High Resolution Imaging Science Experiment (HiRISE) camera. Indeed, as HiRISE has confirmed, this is one very odd-looking crater.
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From a distance, the crater appeared to have a black spot in its center, looking almost like the bulls eye on a dartboard. But on closer scrutiny the spot turned out to be the collapsed roof of an underground cavern. Similar features have been seen on Mars and the moon before and are commonly referred to as "skylights." However, this skylight is unique in that it formed at the base of a larger crater.
This Pavonis Mons skylight is approximately 35 meters (115 feet) in diameter, and by using the shadow on the cavern's floor as a guide, HiRISE scientists have estimated that the feature is around 20 meters (65 feet) deep, according to the mission's website.