NASA’s Mars rover Opportunity was exploring an uncharted Martian valley last month when it encountered a shockingly familiar sight: Streams of rocks and gravel stretched down the hillside of Perseverance Valley — a roughly 600-foot (183 meters) drop down the inner slope of a crater — in seemingly organized rows.

The patterns closely resemble so-called “rock stripes” seen on certain mountains on Earth, NASA said in a statement. These formations usually result when wet soil freezes and thaws repeatedly over many years, NASA said. Perseverance Valley is thought to have been carved hundreds of thousands of years ago by a combination of water, ice and wind — already making the spot unusual by Martian standards, NASA wrote. The presence of these newly discovered stripes further adds to the region’s mystery, researchers said. [The 7 Most Mars-Like Places on Earth]

“Perseverance Valley is a special place,” Opportunity Deputy Principal Investigator Ray Arvidson of Washington University in St. Louis said in the statement. “We already knew it was unlike any place any Mars rover has seen before, even if we don’t yet know how it formed, and now we’re seeing surfaces that look like stone stripes. It’s mysterious. It’s exciting. I think the set of observations we’ll get will enable us to understand it.”

In particular, the rock stripes of Perseverance Valley closely resemble stripes seen inside the cone of Hawaii’s Mauna Kea volcano, according to NASA. There, stripes form when fine-grain soil freezes overnight and expands, pushing up larger chunks of rock on either side. After the soil thaws in the morning, wind and gravity gradually move these larger stones downslope from the moist, fine-grain segments of soil…….more here