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In curious Mars image, NASA asks 'Is that an impact crater?'

Mars is littered with impact craters, but a circular shape seen near the South Pole raises some questions.

Is this an impact crater or something else?

NASA/JPL-Caltech/Univ. of Arizona

"Is that an impact crater?" That's the headline for a NASA image released on Tuesday from the Mars Reconnaissance Orbiter, which is currently traipsing above the Red Planet. It's a fun question. It's also a scientifically interesting one.

The image shows a landscape that looks like the skin of a lizard. There's a circular feature that stands out in a field of roundish raised bumps. Most impact craters, usually caused by meteorites, are fairly easy to spot on Mars. This one is tricky, however. The circular feature is found in Mars' South Pole region.

"Craters in icy terrain are modified by processes that flatten and change them in such a manner that it is hard to say for sure if it had an impact origin," NASA notes.

We don't have a definitive answer to NASA's question. The space agency only concludes that it "might be an impact structure." That gives us some entertaining leeway for wild, unfounded speculation: Maybe it's a UFO landing pattern. Perhaps it's the entrance to an alien base. More likely it's an interesting quirk in the polar landscape or it's NASA's first guess: an impact crater.