NASA’s longest-serving Mars rover has returned pictures of a mysterious rock formation similar to those found on Earth’s mountains – a discovery scientists believe could point to the presence of water on the Red Planet.

The space agency’s Opportunity rover celebrated its 5,000th Martian day on the surface of the planet by beaming back images of a series of corrugated “rock stripes” on the slopes of an area known as Perseverance Valley.

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“Perseverance Valley is a special place, like having a new mission again after all these years,” said Ray Arvidson, the deputy principal investigator from Washington University in the US. “We already knew it was unlike any place any Mars rover has seen before, even if we don’t yet know how it formed, and now we’re seeing surfaces that look like stone stripes. It’s mysterious.”

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The stripes are reminiscent of a similar feature found on Earth when there is repeated freeze and thaw cycles of wet soil. However, the Opportunity team have not ruled out other factors for the Mars formations, including wind, materials shifting downhill or other natural processes. In a statement about the find, NASA also released a comparative image of rock stripes from the volcanic cone on Mauna Kea in Hawaii.

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Opportunity landed on Mars in January 2004 for what was expected to be a 90 Martian-day mission. It is currently investigating Perseverance Valley which descends the slope of the western rim of 22km-wide Endeavour Crater.

The search for water on the Red Planet has progressed in recent times. New research released last month suggests that Mars has ice sheets more than 100 meters (328ft) beneath the surface, offering a potential water source for future explorers.

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