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A martian rock with the appearance of a jelly doughnut has left scientists completely baffled.

The origin and makeup of the object have defied explanation since it was discovered by the Opportunity rover.

Experts said they were “completely confused” by the rock after it appeared on outcrop which had been empty just days earlier.

Lead Mars Exploration rover scientist Steve Squyres said the Red Planet “keeps throwing new things at us”.

The images, taken no more than a couple of weeks ago, are monitored by the Jet Propulsion Laboratory in California.

(Image: PA)

Mr Squyres said: “We saw this rock just sitting here. It looks white around the edge in the middle and there’s a low spot in the centre that’s dark red – it looks like a jelly doughnut.

“And it appeared, just plain appeared at that spot – and we haven’t ever driven over that spot.”

The rock, which is being tested by the rover, could have come from a meteor or been flicked out by a wheel.

Mr Squyres said: “It’s like nothing we’ve ever seen before.

“It’s very high in sulphur, it’s very high in magnesium, it’s got twice as much manganese as we’ve ever seen in anything on Mars.

“I don’t know what any of this means. We’re completely confused.”

The rover has spent more than a month photographing the same region of Mars due to bad weather.

Mr Squyres was speaking at an event held by the laboratory to mark the 10th anniversary of the arrival of Opportunity and Spirit - which has lost contact with Earth - on the surface of Mars.