Mysterious blemish ... the “Athabascan enigma”, an unusual circular mound in the middle of a Mars lava field, has NASA scientists scratching their heads. Source: NASA Source: Supplied

The weird circular blemish, some 2km in diameter, recently appeared in an image beamed back from NASA’s Mars Reconnaissance Orbiter.

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It leaps out at the camera in an area otherwise unusually smooth for the Red planet.

And that in itself could be a clue.

Pock-marked Mars ... The unusual circular feature sits starkly in a smooth lava flow in the Mars region of Athabasca. Source: NASA Source: Supplied

“It looks like a circular island surrounded by a “sea” of smooth-looking lava flows,” a NASA statement on the Athabascan ‘enigma’ reads.

It’s just speculation at the moment: It will no doubt occupy geologists for some time to model the possible cases.

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But NASA has an early idea as to what it could be.

“Perhaps lava has intruded underneath this mound and pushed it up from beneath,” the NASA statement reads.

Eye in the sky ... The Mars Reconnaissance Orbiter (MRO) has been beaming back high resolution images of the surface of Mars since 2006. Source: NASA Source: AFP

“It looks as if material is missing from the mound, so it is also possible that there was a significant amount of ice in the mound that was driven out by the heat of the lava.”

Just how lava boiling up from beneath the surface can create such a shape is yet to be determined.

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And it appears not to be the only one

“There are an array of features like this in the region that continue to puzzle scientists,” NASA says.

The image, and others like it, are undergoing intense scrutiny.

The truth is out there …

NASA's MAVEN orbiter has arrived at Mars after a 10-month voyage.