NASA’s Mars Rover Opportunity surprises scientists with observations of “rock stripes”. They resemble stone stripes on some mountain slopes on Earth.

NASA launched Opportunity to Mars in 2003 for what was supposed to be a 90-Martian-day mission. However, the rover has outlived and outperformed expectations and continues to bring us fascinating discoveries.

The Opportunity team calls the latest discovery of the possible rock stripes “surprising.” They compare the ground texture seen in recent images with very distinctive stone stripes on some mountain slopes on Earth that result from repeated cycles of freezing and thawing of wet soil. But it might also be due to the wind, downhill transport, other processes or a combination.

The alternating strips make the Martian stripes with more and less gravel on them. They look a lot like a series of rivulets. NASA also shared a photo of a section of the Mauna Kea volcano to show how the collections of stripes from different planets resemble each other.

This image shows stone stripes on the side of a volcanic cone on Mauna Kea, Hawaii. The stripes are made of small rock fragments and they are aligned downhill as freeze-thaw cycles have lifted them up and out of the finer-grained regolith, and moved them to the sides, forming stone stripes.
Credits: Washington University in St. Louis/NASA

Formation of Stripes

Usually, the repeated freeze and thaw cycles of wet soil cause the stripes on Earth, according to NASA. However, wind, materials shifting downhill or other natural processes may also shape the Mars formations.

“One possible explanation of these stripes is that they are relics from a time of greater obliquity when snow packs on the rim seasonally melted enough to moisten the soil, and then freeze-thaw cycles organized the small rocks into stripes,” Arvidson said. “Gravitational downhill movement may be diffusing them so they don’t look as crisp as when they were fresh.”

Arvidson calls the stripes mysterious and exciting. NASA researchers aren’t sure yet exactly how the stripes might have formed. Opportunity team member Robert Sullivan says scientists are “entertaining multiple hypotheses and gathering more data to figure it out.”

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Thumbnail image: This late-afternoon view from the front Hazard-Avoidance Camera on NASA’s Mars Exploration Rover Opportunity shows a pattern of rock stripes on the ground, a surprise to scientists on the rover team. The rover took the image in January 2018 as it neared Sol 5000. Credits: NASA/JPL-Caltech