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The Curiosity rover has made the most unusual discovery yet on Mars: rocks made of pure sulfur. And it all started when the 1-ton rover ran over a rock and split it open, revealing yellowish-green crystals never seen before on the red planet.
“I think it’s the strangest discovery of the entire mission and the most unexpected,” said Ashwin Vasavada, Curiosity project scientist at NASA’s Jet Propulsion Laboratory in Pasadena, California. “I must say there is a lot of luck involved here. Not every stone has something interesting inside.”
The Curiosity team was eager to have the rover investigate the Gediz Vallis channel, a winding groove that appears to have been created 3 billion years ago by a mix of flowing water and debris. The canal is carved through part of Mount Sharp, 5 kilometers high. The rover has been climbing the mountain since 2014.
White rocks were visible in the distance and mission scientists wanted to get a closer look. JPL rover drivers, who send instructions to Curiosity, made a 90-degree turn to place the robotic explorer in the correct position so its cameras captured a mosaic of the surrounding landscape.
On the morning of May 30, Vasavada and his team looked at Curiosity’s mosaic and saw a rock crushed between the rover’s wheel tracks. A closer image of the rock made the “mind-blowing” discovery clear, he said.
Some of Curiosity’s discoveries, such as lakes that lasted millions of years and the presence of organic materialscontributed to the ultimate goal of the rover’s mission: trying to determine whether Mars hosted habitable environments.
Now, scientists are on a mission to discover what the presence of pure sulfur on Mars means and what it says about the history of the red planet.
An impressive find
Curiosity had already discovered sulfates on Mars, or sulfur-containing salts that form when water evaporates. The team saw evidence of bright white calcium sulfate, also known as gypsum, within fissures on the Martian surface that are essentially hard water deposits left by ancient groundwater flows.
“Nobody had pure sulfur on their bingo card,” Vasavada said.
Sulfur rocks typically have what Vasavada describes as a “beautiful, translucent, crystalline texture,” but weathering on Mars has essentially destroyed the outer portion of the rocks to blend in with the rest of the planet, which largely consists of shades of sulfur. orange.
Team members were surprised twice — once when they saw the “beautiful texture and color inside” the rock and then when they used Curiosity’s instruments to analyze the rock and received data indicating it was pure sulfur, Vasavada said.
Previously, while exploring Mars, NASA’s Spirit rover broke down one of its wheels and had to drag it while using the other five to go backwards. Wheel drag revealed a bright white soil, which turned out to be almost pure silica. The presence of silica suggests that hot springs or steam vents may have existed on Mars, which could have created favorable conditions for microbial life, had it existed on the planet.
The discovery of silica is still one of the most important discoveries of the Spirit rover, which operated on Mars from 2004 to 2011. And Vasavada says it’s what inspired the team to “look back” at the Curiosity rover — otherwise they wouldn’t have seen the crushed sulfur.
“My jaw dropped when I saw the sulfur image,” said Briony Horgan, co-investigator on the Perseverance rover mission and professor of planetary sciences at Purdue University in West Lafayette, Indiana. “Pure elemental sulfur is a very strange discovery because on Earth we mainly find it in places like hydrothermal vents. Think Yellowstone! Therefore, it is a great mystery to me how this rock formed on Mt.
A field of ‘strange rocks’
As it approached the Gediz Vallis channel, Curiosity sent back photos of an unusual sight: a flat area, about half the size of a football field, littered with glowing white rocks the size of a hand.
At first, the team thought the “strange rocks” were part of the canal’s debris, perhaps a layer that water had transported from higher up the mountain, Vasavada said.
But after closer inspection, including the fortuitous crushing of the sulfur rock, the team now thinks the flat, uniform field of rocks formed where they were found, he said.
The team was eager to collect a sample of the rocks to study, but Curiosity was unable to drill into the rocks because they were too small and brittle. To determine what process formed the sulfur rocks, the team considered nearby bedrock.
Pure sulfur only forms under certain conditions on Earth, such as volcanic processes or in hot or cold springs. Depending on the process, different minerals are created at the same time as the sulfur.
On June 18, the team sampled a large canal rock nicknamed “Mammoth Lakes.” An analysis of the rock’s dust, performed by instruments inside the rover’s belly, revealed a greater variety of minerals than ever seen before during the mission, Vasavada said.
“The running joke for us is that we saw almost every mineral we’ve ever seen on the entire mission, but all in this rock,” he said. “It’s almost an abundance of riches.”
Layers of Martian history
Since landing on Mars on August 5, 2012, the Curiosity rover has climbed 2,600 feet (800 meters) to the base of Mount Sharp from the bottom 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 the history of Mars, including periods when the planet was wet and when it became drier.
Lately, Curiosity has been systematically investigating different features of the mountain, such as the Gediz Vallis channel. The channel was formed well past the mountain because it cuts through different layers of Mount Sharp, Vasavada said.
After water and debris carved a trail, they left behind a 2-mile-long ridge of rocks and sediment beneath the canal. Although Curiosity arrived at the canal in March and will likely stay for another month or two, it has been steadily climbing near the debris trail for some time.
Scientists have questioned whether floods or landslides caused the debris, and Curiosity’s investigations have shown that both violent water flows and landslides likely played a role. Some of the rocks are rounded like river stones, suggesting they were carried away by water, but others are more angular, meaning they were probably brought in by dry avalanches.
Then, water penetrated the debris and chemical reactions created “halo” shapes that can be seen in some of the rocks Curiosity studied.
“This has not been a quiet time on Mars,” Becky Williams, a scientist at the Planetary Science Institute in Tucson, Arizona, and deputy principal investigator for Curiosity’s Mast Camera, said in a statement. “There has been an exciting amount of activity here.
We are observing multiple flows in the channel, including energetic floods and rock-rich flows.”
Scientists are eager to discover more details, including how much water was present to help open the canal.
The Gediz Vallis channel has long been of interest to scientists, including Vasavada, who remembers seeing orbital images of the feature long before Curiosity landed on Mars.
“It was always something that was really intriguing,” he said. “I remember when the rover went over the final hill before we got to the canal, and suddenly you could see the landscape and the curved canal. Now, we are actually here, seeing it with our own eyes, so to speak.”
Curiosity’s ongoing journey
There is no definitive proof of how the sulfur was formed, but the team continues to analyze data collected by Curiosity to determine how and when each mineral formed.
“Maybe this rock slab has experienced several different types of environments,” Vasavada said, “and they are overlapping, and now we have to untangle that.”
Curiosity continues to explore the canal for more surprises, and after moving on, the rover will head west to drive along the mountain, rather than straight up, in search of more intriguing geological features.
Despite 12 years of wear and tear, including some “accidents” such as wheel problems and mechanical problems, Curiosity remains in excellent health, Vasavada said.
“I feel very lucky, but we also all feel cautious that the next one might not just be a close call, so we’re trying to make the most of it, and we have this landing spot that’s been so wonderful,” he said. . “I’m glad we chose something that was worth 12 years of science.”
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