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Nasa's Perseverance rover has made plenty of discoveries since it first touched down on Mars three years ago, but its latest find has really surprised scientists.

Last week, the rover spotted a black-and-white striped rock unlike any seen before on Mars - which experts have nicknamed Freya Castle.

Researchers say the loose stone is likely to have come from elsewhere on the planet, given how different it looks to the surrounding bedrock.

They're hoping that the rover might be able to help solve the mystery of Freya Castle in the coming weeks.

The robotic explorer has been on the hunt for ancient rocks that could teach us about the early history of the Red Planet.

Last week, the team behind the rover spotted the unusual stone while Perseverance was driving across pebbly ground - so it decided to take a few pictures of it.

They nicknamed the rock ‘Freya Castle’ and discovered it measures around 20cm in length and has a distinct pattern with alternating black-and-white stripes.

Experts think that Freya Castle has a texture unlike any seen in this part of the planet before, and even perhaps all of Mars.

Scientists haven't been able to find out much about the rock yet, however they think that either igneous or metamorphic processes could have created its stripes.

Since Freya Castle is a loose stone, researchers say it's likely to have come from elsewhere on the planet, given how different it looks to the surrounding bedrock.

They think it could even have rolled downhill from a higher place!

As Perseverance is currently heading uphill, experts hope that the explorer will find more of this type of rock, so that it can discover more about the mysterious striped stone.

Rocks like Freya Castle provide valuable clues into the volcanic and metamorphic processes that shaped Mars billions of years ago.