The Curiosity rover on Mars has photographed strange "stick-like figures" on a rock.
The images were shared on the NASA's website and the rover's Twitter page.
"Each is about a quarter-inch long. Maybe they're crystals?" the Twitter post read. "Or they could be minerals that filled spaces where crystals dissolved away. Stay tuned!"
Curiosity first visited the site earlier in December, but was directed back there on New Year's Eve to check out what NASA called "some very peculiar targets that warranted some additional interrogation".
That's where Curiosity snapped images of the strange markings, each only a few millimetres long but remarkably different to their surroundings.
Followers of the rover on Twitter had the usual out-of-this-world suggestions, including space dinosaur fossils, sandworms and angel turds.
Monty Python comedian Eric Idle pitched in to suggest they were tyre tracks.
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Curiosity, the size of a car, was only expected to survey Mars for two years after it arrived on the red planet in 2012. It's so far lasted five-and-a-half years.