NASA’s Opportunity rover still finding surprises on Mars
NASA’s Opportunity Mars rover continues to make surprising discoveries during its fourteenth year exploring the red Planet. Most recently, the rover has observed evidence of possible “rock strips.” In recent images from the rover, the texture of the ground looks like a smudged version of distinctive stone strips on some mountain slopes on Earth that are the result of reoccurring cycles of freezing and thawing of wet soil.
Opportunity landed on Mars on Jan. 25, 2004. The rover’s prime mission was planned to last 90 Martian days, or “sols.” Saturday, Feb. 16, 2018 was the rover’s 5,000th day on Mars.
Opportunity is currently exploring “Perseverance Valley,” a shallow channel in the rim of Endeavour Crater. The rover has driven more than 28 miles (45 kilometers) from its current location, about one-third of the way down Perseverance Valley.
“Perseverance Valley is a special place, like having a new mission again after all these years,” said Opportunity’s Deputy Principal Investigator Ray Arvidson via an agency-issued release. “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.”
On some slopes within Perseverance Valley, soil and gravel particles seem to have been organized into corrugations, or narrow rows, parallel to the slope that alternated between rows with more gravel and rows with less.
The valley’s origin is still unknown. Researchers with the rover’s team are analyzing various types of evidence that suggests actions if water, ice or wind. The scientists are also considering a range of possible explanations for the strips and are unsure whether this texture results from relatively recent processes on Mars or occurred much earlier in the planet’s history.
Other clues have suggested to researchers that, one the scale of hundreds of thousands of years, Mars goes through cycles when the tilt or obliquity of its axis increases so much that some of the water frozen at the poles sublimates into the atmosphere and then becomes snow or frost which accumulates closer to the equator.
“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.”
Perseverance Valley contains rocks which were carved by sand blowing uphill from the crater floor. Wind may also play an important role in sorting larger particles into rows which parallel the slope.
“Debris from relatively fresh impact craters is scattered over the surface of the area, complicating assessment of effects of wind,” said Opportunity’s science-team member Robert Sullivan of Cornell University, Ithaca, New York. “I don’t know what these stripes are, and I don’t think anyone else knows for sure what they are, so we’re entertaining multiple hypotheses and gathering more data to figure it out.”
Jim Sharkey is a lab assistant, writer and general science enthusiast who grew up in Enid, Oklahoma, the hometown of Skylab and Shuttle astronaut Owen K. Garriott. As a young Star Trek fan he participated in the letter-writing campaign which resulted in the space shuttle prototype being named Enterprise. While his academic studies have ranged from psychology and archaeology to biology, he has never lost his passion for space exploration. Jim began blogging about science, science fiction and futurism in 2004. Jim resides in the San Francisco Bay area and has attended NASA Socials for the Mars Science Laboratory Curiosity rover landing and the NASA LADEE lunar orbiter launch.