NASA’s Curiosity rover makes ‘most unexpected’ discovery on Mars | CNN

Sign up for CNN’s Wonder Theory science newsletter. Explore the universe with news about fascinating discoveries, scientific breakthroughs and more.

CNN
—

The Curiosity rover has made its most unusual discovery yet on Mars: rocks made of pure sulfur. It all started when the one-ton rover accidentally drove over a rock and split it open, revealing yellowish-green crystals never before seen on the Red Planet.

“I think this is the strangest and most unexpected discovery of the entire mission,” said Ashwin Vasavada, Curiosity project scientist at NASA’s Jet Propulsion Laboratory in Pasadena, California. “I have to say there’s a lot of luck involved here. Not every rock has something interesting in it.”

The Curiosity team was eager for the rover to explore the Gediz Vallis channel, a winding groove that appears to have been created 3 billion years ago by a mixture of running water and debris. The channel is carved into part of the 3-mile-high Mount Sharp. 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 get the rover into the right position so its cameras could capture a mosaic of the surrounding landscape.

On the morning of May 30, Vasavada and his team looked at Curiosity’s mosaic and saw a crushed rock amid the rover’s wheel tracks. A closer image of the rock highlighted the “breathtaking” discovery, he said.

Some of Curiosity’s discoveries, such as lakes that lasted for millions of years and the presence of organic material, played a role in the rover’s ultimate mission goal: trying to determine whether Mars supported habitable environments.

Scientists are now on a mission to find out what the presence of pure sulfur on Mars means and what it reveals about the history of the Red Planet.

Curiosity had already discovered sulfates, sulfur-containing salts that form when water evaporates, on Mars. The team observed traces of bright white calcium sulfate, also known as gypsum, in cracks in the Martian surface that are essentially hard water deposits left by ancient groundwater flows.

“No one had pure sulfur on their bingo card,” Vasavada said.

Sulfur rocks typically have what Vasavada describes as a “beautiful translucent, crystalline texture,” but erosion on Mars has essentially sandblasted the exterior of the rocks to blend in with the rest of the planet, which is largely composed of shades of orange.

The team members were stunned 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.

While exploring Mars, NASA’s Spirit rover broke one of its wheels and had to drag it while using the other five to back up. The drag from the wheel revealed a bright white soil, which turned out to be nearly pure silica. The presence of silica suggests that hot springs or steam vents may have once existed on Mars, which could have created favorable conditions for microbial life if it existed on the planet.

The silica discovery remains 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 behind” the Curiosity rover — otherwise they wouldn’t have seen the crushed sulfur.

“I was gobsmacked when I saw the sulfur image,” said Briony Horgan, a Perseverance co-investigator and professor of planetary sciences at Purdue University in West Lafayette, Indiana. “Pure elemental sulfur is a very strange discovery because on Earth we find it mostly in places like hydrothermal vents. Think Yellowstone! So it’s a big mystery to me how this rock formed at Mount Sharp.”

As it approached the Gediz Vallis channel, Curiosity sent back images of an unusual sight: a flat area, about half the size of a football field, dotted with bright white boulders the size of a hand.

At first, the team thought the “strange rocks” were part of the canal debris, perhaps a layer that water had carried down from higher up the mountain, Vasavada said.

But after closer inspection, including the chance crushing of the sulfurous rock, the team now believes 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 them, but Curiosity couldn’t drill into the rocks because they were too small and brittle. To determine how the sulfurous rocks formed, the team studied the nearby bedrock instead.

Pure sulfur only forms on Earth under certain conditions, such as volcanic processes or in hot or cold springs. Depending on the process, different minerals are formed along with the sulfur.

On June 18, the team took a sample from a large rock in the canal dubbed “Mammoth Lakes.” An analysis of the rock dust, conducted by instruments in the rover’s belly, revealed a greater variety of minerals than ever seen during the mission, Vasavada said.

“Our greatest joy was to see almost all the minerals that we had already seen during the mission, but all in this rock,” he said. “It’s almost an abundance of riches.”

Since landing on Mars on August 5, 2012, the Curiosity rover has climbed 800 meters (2,600 feet) to the base of Mount Sharp from the floor of Gale Crater. The mountain is the central peak of the crater, which is a vast, ancient, dry 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.

Lately, Curiosity has been systematically studying different features of the mountain, such as the Gediz Vallis channel. The channel formed well after the mountain because it cuts through different layers of Mount Sharp, Vasavada said.

After the water and debris carved out a trail, they left behind a 2-mile (3.2-kilometer) ridge of rock and sediment beneath the channel. Although Curiosity arrived at the channel in March and is likely to stay there for another month or two, it has been steadily climbing alongside the debris trail for some time.

Scientists have debated whether floodwaters or landslides caused the debris, and Curiosity’s research has shown that both violent water flows and landslides likely played a role. Some of the rocks are rounded like river pebbles, suggesting they were carried by water, but others are more angular, meaning they were likely carried by dry avalanches.

Then water seeped into the debris and chemical reactions created “halo” shapes that can be seen on some of the rocks studied by Curiosity.

“This was not 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 was some exciting activity here.”
We observe multiple flows in the channel, including energetic floods and boulder-rich flows.

Scientists are eager to discover more details, including how much water was present to help dig the canal in the first place.

The Gediz Vallis channel has long been of interest to scientists, including Vasavada, who recalls observing orbital images of the probe long before Curiosity landed on Mars.

“It was always something that was really intriguing,” he said. “I remember “When the rover went over the last hill before reaching the canal, we could suddenly see the landscape and the curve of the canal. Now we are really there, we see it with our own eyes, so to speak.”

There is no definitive proof of how sulfur 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’re kind of layering on top of each other, and now we have to tease that out.”

Curiosity continues to explore the channel for new surprises, and after continuing on its path, the rover will head west to hug the mountainside, rather than going straight up, to look for more intriguing geological features.

Despite 12 years of wear and tear, including a few “near misses” such as wheel problems and mechanical issues, Curiosity remains in excellent health, Vasavada said.

“I feel very fortunate, but we all realize that the next mission may not be easy. So we try to make the most of it. We have a landing site that has proven to be so wonderful,” he said. “I’m glad we chose a site that represents 12 years of scientific research.”