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Curiosity Discovers Pure Sulfur on Mars in a Martian Rock: Why It’s Unique

Credit: NASA/JPL–Caltech

The Rover Curiosity NASA has observed for the first time yellow crystals of elemental sulfur (i.e. composed only of this element) on the surface of Marsexposed by the breaking of a rock as it passes. Although it has been known for over fifty years that Mars is a planet rich in sulfur compoundsthis element had never been observed on the red planet in its pure form. NASA scientists are now busy searching for an explanation for this unexpected discovery.

Curiosity’s Discovery of Sulfur Crystals

In almost 12 years of an exploratory mission on the Martian soil, the rover Curiosity from the NASA has played a crucial role in broadening our understanding of the past of the red planet. He found numerous evidences of the water passage on its surface and discovered organic molecules inside the rocks. These revelations have opened the way to new theories about the possibility that Mars was once a planet more hospitable compared to current conditions.

A new astonishing discovery was added to Curiosity’s already long list of successes on June 7, 2024, when the MastCam mounted on the rover sent high-resolution photos of a fractured rockinside which they were visible yellow sulfur crystals. This represents the first time that the mineral, consisting of sulfur in its purest form was found on Mars. The crystals were discovered after the Curiosity rover itself shattered the rock as it passed over it on May 30, 2024.

The crystal cluster is approximately 100 mm wide. 13 centimeters. In the photos, the color of the crystals has been slightly altered to simulate how they would appear to the human eye on Earth, adjusting for Martian lighting conditions. The chemical composition, confirmed as sulfur, was determined through aX-ray analysis performed by the instrument Alpha Particle X-ray Spectrometer mounted on the rover. The rock in which the minerals were found has been named “Convict Lake“, name inspired by a lake in the Sierra Nevada in California.

Image produced by Curiosity's Mast Camera, before color adjustment. Credit: NASA/JPL–Caltech
Image produced by Curiosity’s Mast Camera, before color adjustment. Credit: NASA/JPL–Caltech

The presence of sulfur-based compounds on the red planet

Although this discovery represents, to date, a one-of-a-kind casethe presence of sulfur-based compounds on Mars has been known for almost 50 years. In the 1976the first mission Viking revealed that the Martian soils are rich in sulfur and chlorine. Numerous subsequent discoveries, made both through analysis of soils and rocks directly on Mars by the rovers, and through the study of Martian meteorites found on Earth, have strengthened the hypothesis that Mars is a planet particularly rich in sulfur.

Since October 2023, the Curiosity rover has begun exploring the Gediz Valley Channela serpentine valley reminiscent of terrestrial river channels. Right next to the channel is a topographic ridge where exposed rocks rich in hydrated sulphate mineralsIt is hypothesized that these rocks were formed approximately 3 billion years agofollowing of the evaporation of large masses of surface water during Mars’ transition to a arid climate. This same process is also known on Earthwhere it gave rise to numerous formations evaporitic rocks rich in sulphates.

sulfur map mars
Credit: NASA

While the presence of sulfur is well known in the area where the Curiosity rover is currently located, the discovery of elemental sulfur crystals is a completely unexpected novelty. The surprise is palpable in the words of Ashwin VasavadaNASA scientist involved in the Curiosity project: “Finding a field of rocks made of pure sulfur is like finding an oasis in the desert. It shouldn’t be there, so now we have to explain it. Discovering strange and unexpected things is what makes planetary exploration so exciting..”

Origin and characteristics of sulfur-containing minerals

Unlike sulphates, such as plasterL’anhydrite and the baritewhich are minerals composed of sulfur, oxygen, and various other elements, including barium, calcium, and hydrogen, elemental sulfur minerals consist exclusively of sulfur atoms. On Earth, these have a color yellow brilliantAnd odorless and is mainly formed in the vicinity of volcanic vents and fumarolesor in the presence of hydrothermal flows or from the chemical degradation of sulphates on the surface. It is not a very common mineral and is often found underground, inside fractures and cavities.

Sulfur crystals on Earth. Via Wikimedia Commons
Sulfur crystals on Earth. Via Wikimedia Commons

The reasons why these minerals were found on the surface of Mars, and their relationship to other sulfur-based minerals, remain unclear and are currently being investigated by NASA scientists.

Sources

NASA – NASA News – Salty Region Franz, H.B., King, PL and Gaillard, F., 2019. Sulfur on Mars from the atmosphere to the core. In Volatiles in the Martian crust (pp. 119-183). Elsevier. Geology.com NASA – Curiosity NASA – Where is Curiosity? NASA – Curiosity’s path King, PL and McLennan, SM, 2010. Sulfur on mars. Elements, 6(2), pp.107-112.