On May 30, NASA’s Curiosity Mars rover, currently exploring Gale Crater on the red planet, drove over a small rock on the Martian surface. The rock cracked open while driving over the rock, revealing its interior composition.
Scientists on Curiosity’s team were stunned to find yellow sulfur crystals within the rock — the first time these crystals have been spotted on Mars. What’s more, the rock these crystals were found in is made of elemental, or pure, sulfur, unlike the more common sulfur-based minerals Curiosity has previously detected.
Since October 2023, Curiosity has been investigating a region of Gale Crater rich with sulfates, a kind of salt that forms as water evaporates and contains sulfur. Scientists aren’t yet sure if there is a connection between the pure sulfur found in the rock and the sulfur-based rocks that have been found in the past.
Sulfur can only form in a very narrow set of conditions. Curiosity’s scientists haven’t associated the region the rover is exploring with these conditions, which is why the team was shocked by sulfur crystals within the rock. This also isn’t the only rock in this region like this — the team has since identified an entire field of similar rocks in the area around the rover.
The rock Curiosity drove over and subsequently discovered sulfur crystals within. (Credit: NASA/JPL-Caltech/MSSS)
“Finding a field of stones made of pure sulfur is like finding an oasis in the desert. It shouldn’t be there, so now we have to explain it. Discovering strange and unexpected things is what makes planetary exploration so exciting,” said Ashwin Vasavada, a Curiosity project scientist at NASA’s Jet Propulsion Laboratory (JPL) in California.
In September 2014, Curiosity began climbing Mount Sharp (also referred to as “Aeolis Mons”), a large 5.5 km tall mountain in the center of Gale Crater. Along its trek up, Curiosity has explored several different regions of the mountain. Its latest stop was at the Gediz Vallis channel — a large groove in the side of Mount Sharp that winds down to the base of the mountain. Each layer of Mount Sharp that Curiosity encounters on its climb represents a different part of Mars’ history.
Gediz Vallis is one of the main reasons Curiosity’s science team selected Gale Crater as the rover’s landing location before its launch in 2011. The team believes that the channel was carved out by large and long flows of liquid water and debris. In addition to the channel’s geographical nature, the 3.2 km-long ridge of boulders and sediment that extends down the mountain is evidence for these water flows.
When Curiosity arrived at the channel, the team’s main goal was to develop an understanding of how the landscape was carved billions of years ago. Since then, Curiosity has studied whether ancient floods or landslides formed the ridge that rises from the channel’s floor. Curiosity’s findings suggest that both floods and landslides played a role in some way, as some of the sediment and rock piles in the ridge appear to be left by violent flows of water. Other piles appear to be the result of landslides.
Panoramic image of the Gediz Vallis channel, taken by Curiosity. (Credit: NASA/JPL-Caltech/MSSS)
To reach these conclusions, the team commands Curiosity to investigate various rocks found within the debris piles, as the shapes and appearance of these rocks help determine their past and origin. For example, rounded stones that look similar to river rocks were likely carried by water flows, whereas angular rocks were likely deposited by dry avalanches.
Once all of these rocks settled into their mounds within the ridge, water soaked into all of the material. This water then caused chemical reactions that likely created the sulfur-based and pure sulfur rocks that Curiosity is now discovering.
“This was not a quiet period on Mars. There was an exciting amount of activity here. We’re looking at multiple flows down the channel, including energetic floods and boulder-rich flows,” said Planetary Science Institute scientist Becky Williams, who also serves as the deputy principal investigator of Curiosity’s Mastcam instrument.
The team’s initial expectations for their findings in the channel were much less complex than expected. The more Curiosity explores, the more complex the region becomes, and the team was eager to drill into of one of the rocks in the channel to better understand its composition and history.
On June 18, they got their chance as Curiosity drilled into a large sulfur rock named “Mammoth Lakes” using its drill at the end of its two-meter-long robotic arm. Most sulfur rocks are too small and brittle to be drilled into and sampled, but Mammoth Lakes was an exception. Even with Mammoth Lakes’ large size, though, the team had to search for a part of the rock that would allow for safe drilling and sampling. What’s more, the team had to find a safe spot for Curiosity to park while it drilled, as the surrounding surface was loose and sloping.
After drilling into Mammoth Lakes — the 41st time the rover had performed drilling during its mission — the rover poured the now-powdered rock into a set of instruments inside of the rover. Those instruments have since investigated the rock, and teams are now analyzing the data from those instruments to learn more about the rock and its internal composition.
After successfully drilling into Mammoth Lakes, Curiosity drove away and is currently exploring other areas of the channel to learn more about its history and what it means for Martian history.
(Lead image: Curiosity takes a selfie at the Murray Buttes region of Mount Sharp. Credit: NASA/JPL-Caltech)
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