NASA’s Curiosity rover has made an unexpected and fascinating discovery on Mars by cracking open a seemingly ordinary rock and revealing something never before seen on the red planet: pure elemental sulfur.
In May 2024, while traversing the Gediz Vallis Channel, the 899-kilogram rover accidentally rolled over and split a fragile rock, exposing bright yellow crystals of brimstone. Although sulfates—compounds of sulfur mixed with other minerals—are relatively common on Mars, this marks the first time sulfur has been found in its pure, elemental form on the Martian surface.
Even more intriguing, Curiosity’s cameras revealed that the area is strewn with other rocks resembling the one that broke open, suggesting that pure sulfur could be more widespread in this region than previously thought.
“Finding a field of stones made of pure sulfur is like finding an oasis in the desert,” said Ashwin Vasavada, Curiosity’s project scientist at NASA’s Jet Propulsion Laboratory, in July 2024. “It shouldn’t be there, so now we have to explain it. Discovering strange and unexpected things is what makes planetary exploration so exciting.”
On Earth, sulfur is vital for life and plays a key role in forming amino acids and proteins, though it’s typically found in sulfate form. Sulfates on Mars have helped scientists understand the planet’s water history and surface weathering. However, pure sulfur requires a very specific set of geological conditions to form—conditions not previously believed to exist in this part of Mars.
The unexpected finding has raised fresh questions about the geological and possibly volcanic history of the Gediz Vallis Channel. It also underscores how little we still know about the planet’s past and the processes shaping its surface.
Curiosity’s chance encounter with the sulfurous rock also highlights the limitations of remote exploration. Without the rover’s accidental detour and the pressure of its weight cracking the rock, this discovery may have remained hidden for much longer.
While there’s still no evidence of life on Mars, discoveries like this continue to uncover chemical ingredients that are important for life and help researchers piece together the planet’s history.
Curiosity continues its mission to explore Mars, showing how even unplanned moments can lead to groundbreaking discoveries.