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Cave entrance on the flank of Arsia Mons (detail)

Cave entrance on the flank of Arsia Mons (detail)
Cave entrance on the flank of Arsia Mons (detail) At its highest resolution of 25 centimeters per pixel, the HiRISE camera can see the detailed shape of the slightly scalloped edge of a hole on the flank of Mars' Arsia Mons (left), but no amount of image enhancement (right) can bring out any further details inside the hole. That means that the walls of the cave are overhanging -- the cave is larger below the ground than the entrance we can see at the surface -- and that it is very deep. Mars' dusty atmosphere produces enough scattered light that "skylight" would illuminate the floor of a shallow cavern well enough for HiRISE to detect it. NASA / JPL-Caltech / U. Arizona