The Curiosity rover made an accidental discovery on Mars – and uncovered a mineral never before found in its pure form on the Red Planet.

As the rover rolled over the planet's rocky surface on May 30, its wheels crushed a section of rock, revealing crystals of elemental sulfur, an unexpected and rare find, according to a NASA news release.

The find was "completely unexpected," said Abigail Fraeman, the Curiosity mission's deputy project scientist. "It's probably one of the most unusual things that we found the entire 12-year mission."

Although scientists have come across many different types of sulfur on Mars, the discovery marks the first time they found pure sulfur.

"Usually, it's coupled with oxygen and other elements that make it into a salt or something similar, but here, what we found was just chunks of pure sulfur," Fraeman said.

Elemental sulfur is bright yellow and has no odor. It forms in only a narrow combination of conditions – scientists didn't expect to locate such a large amount on Mars.

"It's telling us something new about the history of Mars and what sorts of potentially habitable environments it's sustained in the past," Fraeman said.

Scientists nicknamed the 5-inch sample of yellow sulfur crystals "Convict Lake" after a lake in California's Sierra Nevada mountains, according to NASA.

Curiosity snapped photos of the piece of sulfur using its Mastcam, a camera mounted on its head at around human eye level, with a color quality similar to that of two digital cameras, the news release said. The rover later detected the mineral using its Alpha Particle X-ray Spectrometer, attached to the end of its robotic arm.

Curiosity found the sample as it traversed the Gediz Vallis channel, which runs down Mount Sharp, according to Fraeman. The discovery came after scientists directed Curiosity towards a brightly colored field of rocks, she said.

Curiosity has been climbing the 3-mile-high peak for a decade, the news release said. The area is rich in sulfates, a sulfur-based salt left behind when water dried up billions of years ago.

NASA scientists say the channel is one of the main reasons they sent Curiosity to Mars. They believe it was carved out by streams of water mixed with debris, as evidenced by the rounded rocks found in the channel that were likely shaped by the flow of water, like river stones. Some rocks also have white halo markings, which also indicates water.

Fraeman said it will take more time to figure out what the discovery could mean about the kind of environment that once existed in the area.

"Right now, we're kind of analyzing all of the data we collected and trying to figure out what observations we can make that can either support or cross off some of these environments," she said.

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Curiosity searches for evidence of life on Mars

The discovery came on the 4,208th Martian day of Curiosity's mission, NASA said. The rover landed on the planet's surface nearly 12 years ago with the objective of investigating whether Mars was ever habitable.

And it succeeded – early in the mission, Curiosity uncovered chemical and mineral evidence that the planet's environment was previously habitable for small life forms known as microbes.

"We've certainly found with Curiosity that Mars was not only once habitable, but it was habitable for an extended period of time," Fraeman said.

In 2018, Curiosity found organic molecules in a crater that scientists believe was once a shallow lake. The molecules, similar to the molecular building blocks of Earth's oil and gas, showed that the crater was habitable 3.5 billion years ago, around the same time that life developed on Earth under similar conditions.

The $2.5 billion rover is packed with a wide range of tools, including 17 cameras, and 10 science instruments, including spectrometers, radiation detectors, and sensors to probe the Martian atmosphere and environment.

Fraeman said Curiosity has held up surprisingly well – all of its instruments are working as well as the day it landed. Still, the terrain is filled with surprises.

"On Mars, something catastrophic could happen any day," she said. "We always treat every day as if it's precious."

Cybele Mayes-Osterman is a breaking news reporter for USA Today. Reach her on email at [email protected]. Follow her on X @CybeleMO.