A Surprising Discovery: Pure Sulfur Found On Mars

Unexpected news came from the Red Planet on May 30. As the Curiosity rover traveled through the Gediz Vallis Channel during a typical day of operations, it inadvertently drove over a group of rocks, breaking some of them. This unintentional maneuver revealed something never seen before or expected on Mars: yellow crystals of pure sulfur.

“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 .”

— Curiosity’s project scientist, Ashwin Vasavada of NASA’s Jet Propulsion Laboratory in Southern California

*Yellow sulfur crystals revealed by the Curiosity Rover. Credits: NASA/JPL-Caltech/MSSS*

The Current Location of Curiosity

The Curiosity rover is currently off-roading in the Gediz Vallis Channel, a groove thought to have been formed by flows of liquid water billions of years ago. This channel is located at the base of Mount Sharp, inside Gale Crater. The rover arrived in the crater in August 2012 and has been exploring it ever since.

*View of the Gale Crater,154 kilometers in diameter, at the center the Mount Sharp 5000 mt high. Credits: NASA/JPL*

The mountain is characterized by a series of distinct terrain layers deposited over millions of years of Martian history, exposed after a massive impact that excavated Gale Crater more than 3 billion years ago. Each layer of the mountain represents a different period of Martian history, providing a glimpse into the past that shows the environmental conditions when each layer was deposited.

Illustration of the route driven by NASA's Curiosity rover since landing in 2012. Credits: NASA — *Illustration of the route driven by NASA’s Curiosity rover since landing in 2012. Credits: NASA*

Since 2014, Curiosity’s mission in this area has been to confirm whether the channel was carved by debris flows or an ancient river, as opposed to wind, and more generally to develop a better understanding of how this landscape changed billions of years ago and to determine if there was a time when Mars had conditions that could sustain life. But this time, by pure chance, Curiosity found something that could change a lot of theories.

The Discovery

Since October 2023, the rover has been exploring a sulfate-rich region of Mars. Analysis of the terrain in this region has revealed sulfur-based minerals, in which sulfur combines with other elements to form compounds known as sulfates.

But on May 30, the Curiosity rover accidentally drove over a small rock, breaking it. When scientists examined the rock with the rover’s cameras, they saw unusual yellow crystals in the fractured rock. However, these crystals were too small and fragile for the rover to handle effectively.

Subsequently Curiosity drilled into another nearby rock. It then confirmed that these crystals were composed of pure sulfur. This is the first time that pure sulfur, or elemental sulfur, has been discovered on Mars. Scientists had speculated about the existence of elemental sulfur on the planet, but its presence in surface rocks was unexpected.

*Some samples of pulverized rock captured by Curiosity with its drill. Credits: NASA/JPL-Caltech/MSSS*

Sulfur is usually associated with the smell of rotten eggs, but elemental sulfur is odorless. Furthermore, it only forms under certain conditions, which, according to theories about the history of this location, have never existed.

The discovery could revolutionize our understanding of Martian geology and hydrothermal processes, as well as influence future exploration and sampling missions.

For now, NASA is not advancing any theory for the presence of sulfur, but said that all the new recent discoveries continue to tell a more complex story than the team’s early expectations. For now, we can only wait for future updates.