Mars Opportunity rover has found a weird rock on the red planet that looks like a "jelly doughnut", a discovery that has left scientists baffled.

In a comparison of recent photographs captured by the rover’s panoramic camera, or Pancam, on the 3528th sol or Martian day, of the mission, only bare bedrock can be seen.

However, an image taken 12 days later shows an additional rock about the size of a doughnut, said scientists at NASA’s Jet Propulsion Laboratory in California.

"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," Lead Mars Exploration rover scientist Steve Squyres said.

"And it appeared, just plain appeared at that spot — and we haven’t ever driven over that spot," Squyres said.

The rock, named 'Pinnacle Island', could have come from a meteor or been flicked out by a wheel, 'mirror.co.uk' reported.

"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," Squyres said.

The team will now examine the rock to study its elemental composition.

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