NASA's Mars Reconnaissance Orbiter took this photo of a cave skylight on the southeastern flank of Pavonis Mons, a large volcano in Mars' Tharsis Region. The pit is about 180 meters wide.
NASA is mapping out a strategy to return bits of rock and soil from the Martian surface to Earth, but the most intriguing Red Planet samples lie in underground caverns, some scientists say.
The space agency's next steps at Mars are geared toward mounting a sample-return mission, which is widely viewed as the best way to look for signs of Red Planet life. Such signs are perhaps more likely to be found in material pulled from the subsurface, so some researchers hope NASA's first Martian sample-return effort won't be its last.
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