A rock on Mars recently revealed an unexpected treasure after Curiosity accidentally cracked through its seemingly ordinary exterior.

When the rover, weighing 899 kilograms (1,982 pounds), rolled over the rock, it broke open to reveal yellow crystals of elemental sulfur, or brimstone. While sulfates are relatively common on Mars, this is the first discovery of sulfur in its pure elemental form on the planet.

What’s more intriguing is that the Gediz Vallis Channel, where Curiosity encountered the rock, is scattered with rocks that resemble the sulfur-containing rock before it was fortuitously crushed. This suggests that elemental sulfur might be more common in this area than previously thought.

“Finding a field of stones made of pure sulfur is like finding an oasis in the desert,” said Ashwin Vasavada, Curiosity project scientist at NASA’s Jet Propulsion Laboratory. “It shouldn’t be there, so now we have to explain it. Discovering strange and unexpected things is what makes planetary exploration so exciting.

Sulfates are salts formed when sulfur, typically in compound form, combines with other minerals in water. When the water evaporates, the minerals mix and dry out, leaving behind sulfates.

These sulfate minerals provide valuable information about Mars, such as its water history and weathering processes over time.

Pure sulfur, however, only forms under a very specific set of conditions, which are not known to have occurred in the region of Mars where Curiosity made its discovery.

Admittedly, there are many aspects of Mars’ geological history that remain unknown, but the discovery of large amounts of pure sulfur on the Martian surface suggests there are significant gaps in our understanding.

Understanding sulfur is crucial as it is an essential element for all life, typically absorbed as sulfates and used to synthesize two of the essential amino acids required for protein production.

While the presence of sulfates on Mars has been known for some time, this discovery doesn’t provide new insights in that regard. We have yet to find any signs of life on Mars, but we continue to encounter elements that would be useful to living organisms, such as certain chemicals, water, and evidence of past habitable conditions.

Our ability to study Mars is somewhat limited from Earth. Curiosity’s instruments could analyze and identify the sulfurous rocks in the Gediz Vallis Channel, but if the rover hadn’t happened to crack one open, it might have taken much longer to make this discovery.

The next step is to determine how this sulfur came to be on Mars, given our current understanding of the planet. This will require further work, potentially involving detailed modeling of Mars’s geological evolution.

Meanwhile, Curiosity will keep gathering data. The Gediz Vallis channel, an area steeped in Martian history, is an ancient waterway with rocks bearing the marks of a river that flowed over them billions of years ago.

Curiosity has drilled into one of these rocks, collecting a powdered sample from its interior for chemical analysis. The rover is now moving deeper along the channel, eager to uncover what other surprises may lie just around the next bend.