Rover's Accidental Discovery: Amazing Pure Sulfur yellowish-green Crystals on Mars

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NASA’s Curiosity rover has uncovered an extraordinary geological feature on Mars: rocks composed of pure sulfur. This surprising discovery, which occurred when the rover happened to drive over a rock and crack it open, has captivated scientists and shed new light on the Martian environment.

 

 

The unexpected find of yellowish-green crystals, never before seen on the red planet, was described by Ashwin Vasavada, Curiosity project scientist at NASA’s Jet Propulsion Laboratory in Pasadena, California, as the "strangest" and "most unexpected" of the mission. "I have to say, there’s a lot of luck involved here. Not every rock has something interesting inside," Vasavada remarked, underscoring the fortuitous nature of the discovery.

 

 

The Curiosity team had been eager to investigate the Gediz Vallis channel, a winding groove on Mount Sharp that appears to have been created three billion years ago by a combination of flowing water and debris. This channel is carved into the 3-mile-tall Mount Sharp, which Curiosity has been scaling since 2014. Visible in the distance were white stones, prompting mission scientists to seek a closer look.

 

 

The rover drivers at JPL, who send instructions to Curiosity, executed a 90-degree turn to position the rover’s cameras for a detailed mosaic of the surrounding landscape. On the morning of May 30, Vasavada and his team examined Curiosity’s mosaic and noticed a crushed rock amidst the rover’s wheel tracks. A closer inspection of the rock revealed the "mind-blowing" find of pure sulfur crystals.

 

 

Curiosity’s mission has always been to determine whether Mars once hosted habitable environments, and some of its previous discoveries, such as lakes that lasted millions of years and the presence of organic materials, have played into this goal. The presence of pure sulfur, however, adds a new layer of complexity to the planet’s geological history. "No one had pure sulfur on their bingo card," Vasavada quipped, highlighting the unexpected nature of the discovery.

 

 

Sulfur rocks on Earth typically have a "beautiful, translucent and crystalline texture," but weathering on Mars has essentially sandblasted the exterior of these rocks to blend in with the planet’s predominant shades of orange. The team was doubly stunned when they used Curiosity’s instruments to analyze the rock and received data indicating it was pure sulfur. "My jaw dropped when I saw the image of the sulfur," said Briony Horgan, a co-investigator on the Perseverance rover mission and professor of planetary science at Purdue University in West Lafayette, Indiana. She noted, "Pure elemental sulfur is a very weird finding because on Earth we mostly find it in places like hydrothermal vents. Think Yellowstone! So it’s a big mystery to me as to how this rock formed in Mt. Sharp."

 

This discovery is reminiscent of a significant finding by NASA’s Spirit rover, which in 2008, while dragging a broken wheel, revealed bright white soil that turned out to be nearly pure silica. The presence of silica suggested the past existence of hot springs or steam vents on Mars, environments that could have been conducive to microbial life if it ever existed on the planet. The silica discovery remains one of Spirit’s most important findings, and Vasavada noted that it inspired the team to "look behind" the Curiosity rover, leading to the sulfur discovery. "I feel very lucky, but also we all feel cautious that the next one may not be only a close call, so we’re trying to make the most of it, and we have this landing site that’s been so wonderful," he said.

 

While approaching the Gediz Vallis channel, Curiosity sent back images of an unusual sight: a flat area about half the size of a football field, scattered with bright white hand-sized rocks. Initially, the team thought these "strange rocks" were part of the debris from the channel, possibly transported by water from higher up the mountain. However, upon closer inspection and the fortuitous crushing of the sulfur rock, the team now believes the flat, uniform field of rocks formed in their current location.

 

The team was eager to take a sample of the rocks for further study, but Curiosity could not drill into the rocks because they were too small and brittle. Instead, the team analyzed nearby bedrock to determine the processes that formed the sulfur rocks. Pure sulfur on Earth only forms under certain conditions, such as volcanic processes or in hot or cold springs, and depending on the process, different minerals are created alongside the sulfur.

 

On June 18, the team sampled a large rock from the channel, nicknamed "Mammoth Lakes." An analysis of the rock’s dust, carried out by instruments within the rover’s belly, revealed a larger variety of minerals than ever seen before during the mission. "The running joke for us was we almost saw every mineral we’ve ever seen in the whole mission but all in this rock," Vasavada said. "It’s almost an abundance of riches."

 

Since landing on Mars on August 5, 2012, the Curiosity rover has ascended 2,600 feet up the base of Mount Sharp from the floor of Gale Crater. The mountain is a central peak of the crater, which is a vast, dry ancient lake bed. Each layer of Mount Sharp tells a different story about Mars’ history, including periods when the planet was wet and when it became drier. Curiosity has been systematically investigating different features of the mountain, such as the Gediz Vallis channel, which was formed well after the mountain because it carves through different layers of Mount Sharp. After water and debris carved a trail, they left behind a 2-mile ridge of boulders and sediment below the channel. Although Curiosity arrived at the channel in March and is likely to stay for another month or two, it has been steadily climbing next to the debris trail for a while.

 

Scientists have wondered whether floodwaters or landslides caused the debris, and Curiosity’s investigations have shown that both violent water flows and landslides likely played a part. Some of the rocks are rounded like river rocks, suggesting they were carried by water, but others are more angular, meaning they were likely delivered by dry avalanches. Then, water soaked into the debris, and chemical reactions created "halo" shapes that can be seen on some of the rocks that Curiosity has studied. "This was not a quiet period on Mars," said Becky Williams, a scientist with the Planetary Science Institute in Tucson, Arizona, and the deputy principal investigator of Curiosity’s Mast Camera, in a statement. "There was an exciting amount of activity here. We’re looking at multiple flows down the channel, including energetic floods and boulder-rich flows."

 

Scientists are eager to uncover more details, including how much water was present to help carve the channel in the first place. Gediz Vallis channel has long been of interest to scientists, including Vasavada, who recalls looking at orbital images of the feature well before Curiosity landed on Mars. "It’s always been something that’s just been really intriguing," he said. "I remember when the rover kind of rolled over the final hill before we got to the channel, and you could all of a sudden see the landscape and the curved channel. Now, we’re actually here, seeing it with our own eyes, so to speak."

 

There is no definitive explanation yet for how the sulfur was formed, but the team continues to analyze the data collected by Curiosity to determine how and when each mineral formed. "Maybe this rock slab has experienced multiple different kinds of environments," Vasavada said, "and they’re sort of overprinting each other, and now we have to unravel that." As Curiosity continues to explore the channel, looking for more surprises, the rover will eventually head west to drive along the mountain rather than straight up, to seek out more intriguing geological features.

 

Despite 12 years of wear and tear, including some "close calls" such as wheel issues and mechanical problems, Curiosity remains in great health, according to Vasavada. "I feel very lucky, but also we all feel cautious that the next one may not be only a close call, so we’re trying to make the most of it, and we have this landing site that’s been so wonderful," he said. "I’m glad we chose something that was 12 years’ worth of science."

 

Credit: CNN | NYP 2024-07-22

 

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