On Jan. 8, NASA’s rover, Opportunity, discovered a mysterious white rock that appeared next to the rover on Mars 13 days after the rover took a photograph on a Dec. 26.

Ten years ago, Opportunity landed on Mars’ Meridiani Planum crater for signs of past water, said Reuters. NASA’s other rover, Curiosity, had landed on Mars in 2012 to look for habitable environments on the other side of Mars.

While Opportunity was exploring, it took a picture of this rock which has yet to be classified.

So far, scientists have said that it’s the size of a doughnut, with white coloring on the outside and red on the inside. Space.com quotes Steve Squyres, the rover’s lead scientist at Cornell University in Ithaca, N.Y., in attempting to explain the rock’s origin.

“It looks like a jelly donut,” said Squyres. “And it appeared, it just plain appeared, at that spot and we haven’t driven over that spot.”

According to Reuters, scientists have guessed that Opportunity probably flipped the rock over during its excavations. Or perhaps it was dislodged during a meteorite landing. In the meantime, scientists have named it “Pinnacle Island.”

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