Bull's-Eye on Mars Revealed

A striking bull's-eye on Mars ? evidence of a massive Martian impact ? has been beamed to Earth from the high-powered camera onboard a powerful NASA spacecraft orbiting the red planet.

The photo of the unusual-looking crater was taken by the High Resolution Imaging Science Experiment (HiRISE) ?on the Mars Reconnaissance Orbiter. [Mars bull's-eye crater photo]

Scientists are now trying to determine what could have caused the central pit within the Mars impact crater. In other words, was it the product of unusual subsurface layering, or was it created by a fortuitous second impact?

"Impacts into layers of alternately strong and weak material ? for example, ice rich versus non-ice-rich ? produce terracing such as that seen between the inner pit and the outer rim," ?wrote Sarah Milkovich, a member of the HiRISE science team at the University of Arizona, in a statement.

Previously, scientists have examined terraced craters in order to estimate the thickness of lava flows on the moon and elsewhere, she explained.

"Uneven sublimation and periglacial erosion of exposed ice-rich material in the interior of the crater may explain why the small central pit is slightly offset from center relative to the terrace and rim of the larger crater," Milkovich wrote.

The pit in the center of the main feature could also be explained by a later impact that struck inside and slightly off-center, she added.?

"It has a raised rim, which is characteristic of impact craters and is difficult to explain with a layered target," Milkovich explained. "While no ejecta from this later impact can be seen, the ejecta could have been removed by extensive periglacial modification. Additionally, the floor fill around the inner crater resembles impact ejects elsewhere at this latitude, and some of the 'landslides' to the East could be flow-back of ejecta off the walls of the larger crater."

NASA released the photo recently, though the Mars Reconnaissance Orbiter actually snapped the bull's-eye crater on July 9, at 46.6 degrees latitude (centered) and 194.9 degrees longitude (East) on the Martian surface.

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