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A large impact crater found on Mars' southern highlands, Rabe Crater's brilliant blue color is shown in this photograph first released by NASA in October 2007. "Dark dunes -- accumulations of wind blown sand -- cover part of [the] crater's floor, and contrast with the surrounding bright-colored outcrops," NASA explained. "The extreme close-up view reveals a thumbprint-like texture of smaller ridges and troughs covering the surfaces of the larger dunes. These smaller ripples are also formed and shaped by blowing wind in the thin atmosphere of Mars."

NASA suspects that this deep depression has acted as a sand trap, capturing particles that probably aren't local to the Rabe Crater, resulting in the sharp contrast between dark and light seen here.

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Image: NASA.

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