Something has been found on Mars that shouldn’t have been there. Now scientists know why

This discovery immediately baffled the scientists. On Mars, sulphur is usually found as part of minerals, rather than as individual crystals. Researchers now believe that the answer may lie in an event that took place millions of years ago.

The study has been published in the journal *Icarus*.

Why the discovery was so unusual

On Earth, deposits of pure sulphur are often associated with volcanoes or hot springs.

But in Gale Crater, where Curiosity is operating, there are no signs of such processes. Therefore, the presence of pure sulphur here seemed virtually inexplicable.

What’s more, near the first discovery, the rover also found other rocks containing sulphur.

Suspicion fell on an ancient asteroid

The researchers turned their attention to a small, eroded crater about 390 metres in diameter, situated higher up the slope.

They hypothesised that an asteroid had once struck this spot.

Computer modelling showed that the impact could have melted the sulphur-rich rocks. The resulting molten sulphur flowed down the slope, then cooled and turned into the very crystals that Curiosity happened to discover millions of years later.

Why sulphur could flow like water

At temperatures above 115 °C, molten sulphur becomes very fluid — almost like water.

Therefore, following the asteroid impact, it could well have spread across the surface until it gradually solidified.

Calculations have shown that this mechanism could explain the formation of deposits of pure sulphur, provided the original rock contained very large quantities of this element.

The authors emphasise that this is still a hypothesis, not a proven fact.

The model is based on computer simulations and has a number of limitations. For example, scientists are not yet able to accurately model the behaviour of sulphur under the extremely high pressures generated by asteroid impacts.

Curiosity itself will be able to test the hypothesis. In the near future, the rover is due to explore the area where the ancient impact is thought to have taken place.

If sulphur-rich rocks are indeed found there, the asteroid theory will receive strong support.

Why this is important

Pure sulphur has become one of Curiosity’s most unexpected discoveries in recent years.

If the hypothesis is confirmed, scientists will gain a new explanation for how unusual deposits of chemical elements form on Mars following cosmic collisions. This will also help to better understand the geological history of the Red Planet.

Background

The Curiosity rover has been exploring Gale Crater since 2012. Its main objective is to determine whether conditions suitable for life existed on ancient Mars.

Crystals of pure sulphur were discovered in the summer of 2024 after one of the rover’s wheels accidentally split a rock.

Source

Luca Maggioni et al. Impact-induced melting of materials with sparse thermodynamic data: The case of native sulphur on Mars. Icarus (2026).