When NASA's next rover, now dubbed Curiosity, arrives at Mars on 6 August, its prime target will be the base of Mount Sharp, the 5-kilometer-high mound of sediments in the middle of Gale crater. Mars researchers have no idea how those sediments got there. But a pair of geologists is now suggesting that at least the top third of Mount Sharp is volcanic ash that fell out of the sky surprisingly early in Mars's history. The so-called Medusae Fossae Formation (left) covers a third of the martian equatorial region, some patches of it being near Gale crater. Orbital imaging suggests it is ash from massive eruptions. It bears a striking resemblance to layered deposits high up Mount Sharp (right), the researchers note online today in Science. By counting accumulated impact craters, the team has also found that the two deposits were laid down at about the same time, 3.8 billion years ago. If they are indeed one in the same deposit, Curiosity could probe beneath the thin coating of dust that obscures all of the deposit and confirm its true nature. That's assuming the rover survives long enough to range far up the mysterious mound.
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