NASA's Curiosity rover, which will be sent to Mars in 2022, made a new discovery when it broke off while passing over a rock. Inside were some yellowish-green crystals, which had never been found before on the red planet. According to NASAIt is pure sulfur.

“I think it was the strangest and most unexpected discovery of the entire mission,” said Ashwin Vasavada, a scientist at NASA's Jet Propulsion Laboratory in California. CNN International“I have to say there is a lot of luck involved here,” he added. “Not all rocks have something interesting in them.”

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The discovery was made on May 30, seven months after Curiosity began exploring a region of Mars rich in sulfates, a type of salt that contains sulfur and forms when water evaporates, according to NASA’s website. While previous discoveries have been of sulfur-based minerals, this one “is made of elemental, or pure, sulfur,” according to the agency. “It is unclear what relationship, if any, this elemental sulfur has to other sulfur-based minerals in the region,” the post reads.

“Finding a field of rocks made of pure sulfur is like finding an oasis in the desert,” added scientist Ashwin Vasavada. “It shouldn’t be there, so now we have to explain it. Finding strange and unexpected things is what makes planetary exploration so exciting.”