These yellow crystals were uncovered after NASA’s Curiosity rover happened to pass over a rock and broke it off on May 30. Using a tool on the rover’s arm, scientists later determined the crystals were elemental sulfur — the first time this type of sulfur has been found on the Red Planet. Credit: NASA/JPL-Caltech/MSSS
Among many recent findings, the rover found rocks made of pure sulfur — the first of their kind on the Red Planet.
NASAcuriousity Mars A spacecraft recently discovered yellow sulfur crystals in a rock on Mars, revealing pure sulfur in a region known for sulfate salts. The unexpected discovery was made while exploring the Geddes Vallis channel on Mount Sharp, which has been linked to ancient water flows and the possibility of microbial life. The discovery raises new questions about the geological history and conditions of Mars.
Unprecedented discovery on Mars
Scientists were stunned on May 30 when a rock NASA’s Curiosity rover passed over on Mars cracked open to reveal something never before seen on the Red Planet: yellow sulfur crystals.
Since October 2023, the rover has been exploring a region of Mars rich in sulfates, a type of salt that contains sulfur and forms as water evaporates. But while previous discoveries were of sulfur-based minerals — in other words, a mixture of sulfur and other materials — the rock Curiosity recently excavated is made of elemental, or pure, sulfur. It’s not clear what, if any, relationship elemental sulfur has with the other sulfur-based minerals in the region.
While people associate sulfur with the smell of rotten eggs (a product of hydrogen sulfide gas), elemental sulfur is odorless. The sulfur forms in a narrow range of conditions that scientists have not linked to the history of this site. Curiosity found a lot of it—a whole field of shiny rocks that looked similar to the ones the rover crushed.
NASA’s Curiosity rover took this close-up of a rock nicknamed “Ice Lake” on June 8, 2024, the mission’s 4209th sol, or solar day. Nine days earlier, the rover crushed a similar-looking rock, revealing a crystalline texture — and elemental sulfur — inside. Image credit: NASA/JPL-Caltech/Mars Science and Social Science Center
“Finding a field of rocks made of pure sulfur is like finding an oasis in the desert,” said Ashwin Vasavada, Curiosity’s project scientist from NASA’s Jet Propulsion Laboratory in Southern California. “It shouldn’t be there, so now we have to explain it. Finding strange and unexpected things is what makes planetary exploration so exciting.”
It’s one of several discoveries Curiosity made while off-roading inside Geddes Vallis, a canyon that runs down a 3-mile-high (5-kilometer-high) section of Mount Sharp (see image below), on whose base the rover is perched. Ascending since 2014Each layer of the mountain represents a different period in Mars’ history. Curiosity’s mission is to study when and where the planet’s ancient terrain could have provided the nutrients needed for microbial life, if it ever formed on Mars.
Mount Sharp rises about 3.4 miles (5.5 kilometers) above the floor of Gale Crater. This oblique view of Mount Sharp was obtained from a combination of elevation and imaging data from three Mars orbiters. The view looks southeast. Gale Crater is 96 miles (154 kilometers) in diameter. Credit: NASA/JPL-Caltech/ESA/DLR/Freie Universität Berlin/Space and Social Science Service
Floods and avalanches
The Geddes Vallis Canal, which was spotted from space years before Curiosity launched, was one of the main reasons the science team visited this part of Mars. Scientists believe the canal was carved by flows of liquid water and debris that left a trail of rocks and sediments running two miles down the mountainside below the canal. The goal was to better understand how this landscape has changed over billions of years, and while recent evidence has helped, there’s still much to learn from the dramatic landscape.
Since Curiosity arrived in the canal earlier this year, scientists have been studying whether ancient floodwaters or landslides created the large piles of debris rising from the canal floor here. The latest evidence from Curiosity suggests both played a role: Some of the piles were likely left behind by violent flows of water and debris, while others appear to be the result of localized landslides.
Take a tour of this 360-degree video to explore the Geddes Vallis Channel, the site where NASA’s Curiosity rover discovered sulfur crystals and drilled rock sample number 41. The images that make up this mosaic were captured by the rover’s MastCam in June. Credit: NASA/Jet Propulsion Laboratory-Caltech/MSSS
These conclusions are based on the rocks in the debris piles: while the stones carried by water flows become rounded like river rocks, some debris piles are filled with more angular rocks that may have been deposited by dry avalanches.
Eventually, water seeped into all the material that settled here. Chemical reactions caused by the water bleached white “halo” patterns in some of the rocks. Erosion by wind and sand exposed these halo patterns over time.
“This has not been a quiet period on Mars,” said Becky Williams, a scientist at the Planetary Science Institute in Tucson, Arizona, and deputy principal investigator for Curiosity’s MastCam. “There has been an exciting amount of activity here. We’re looking at multiple flows down the channel, including active floods and rock-rich flows.”
NASA’s Curiosity rover captured this image of the Geddes Vallis Channel on March 31. The area was likely formed by massive flooding of water and debris that deposited rocks into hills within the channel.
Copyright: NASA/JPL-Caltech/Space Science and Social Sciences Program
hole in 41
All this evidence of water continues to tell a more complex story than the team had initially anticipated, and they were eager to take a sample of rock from the channel to learn more. On June 18, they got the chance.
While the sulfur rocks were too small and fragile to be sampled with a drill, a large rock dubbed “Mammoth Lakes” was spotted nearby. Rover engineers had to find a section of rock that would allow for safe drilling and a place to park the vehicles on the sloping surface.
After Curiosity drilled Hole 41 with the powerful drill at the end of its 2-meter-long robotic arm, the six-wheeled rover transferred crushed rock to tools inside its belly for further analysis so scientists could determine what the rocks were made of.
Since then, Curiosity has moved away from Mammoth Lakes and is now on its way to see what other surprises await discovery inside the canal.
About NASA’s Curiosity Rover
NASA’s Curiosity rover, officially known as the Mars Science Laboratory (MSL), is a car-sized robotic rover that landed on Gale Crater on Mars on August 6, 2012. Its primary mission is to investigate the climate and geology of Mars, specifically to determine whether the planet has ever had conditions suitable for microbial life. Equipped with a suite of scientific instruments, Curiosity can take panoramic images, analyze mineral compositions, monitor environmental conditions, and drill into Martian rocks to collect samples.
Since landing, Curiosity has made important discoveries, including evidence of ancient water flows that suggest Mars may have once supported life. Managed by NASA’s Jet Propulsion Laboratory, the rover incorporates advanced technology from previous Mars missions, enhancing its mobility and ability to withstand the harsh Martian environment. Curiosity continues to send valuable data back to Earth, greatly expanding our understanding of the Red Planet.