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It's the pits on Mars

NASA / JPL / Univ. of Ariz.
 Sunlight is reflected off the wall of a Martian pit.

Fresh imagery from NASA's Mars Reconnaissance Orbiter shows that the strange holes detected in earlier pictures of the Red Planet's surface are most likely vertical pits rather than openings to underground cave networks, as some had previously speculated.

Here's the latest from the imaging team for the MRO's high-resolution camera, or HiRISE, posted today on its Web site:

"Dark pits on some of the Martian volcanoes have been speculated to be entrances into caves. A previous HiRISE image, looking essentially straight down, saw only darkness in this pit.

"This time the pit was imaged from the west. Since the picture was taken at about 2:30 p.m. local (Mars) time, the sun was also shining from the west. We can now see the eastern wall of the pit catching the sunlight.

"This confirms that this pit is essentially a vertical shaft cut through the lava flows on the flank of the volcano. Such pits form on similar volcanoes in Hawaii and are called 'pit craters.' They generally do not connect to long open caverns but are the result of deep underground collapse. From the shadow of the rim cast onto the wall of the pit we can calculate that the pit is at least 78 meters (255 feet) deep. The pit is 150 by 157 meters (492 by 515 feet) across."