Curiosity rover detects elemental sulphur on Mars.

NASA's Curiosity Rover has detected crystals of elemental sulphur on the surface of Mars, the first time sulphur has been detected as a pure element on the planet. The crystals were observed at a location within Gale Crater called Convict Lake on 7 Jun 2024, and form a patch about 12 cm across. The crystals are thought to have been exposed by the rover itself driving over a rock and crushing it several days previously.

A patch of minerals including crystals of pure elemental sulphur on the surface of Mars. The image has been colour enhanced to for the benefit of Human eyes; the rover used an X-ray spectrophotometer to detect the element. NASA/JPL/CalTech/Malin Space Science Systems. 

The presence of sulphur on Mars is hardly surprising not surprising. The element is one of the most common in the universe and has been detected on all planets in the Solar System, as well as meteorites, asteroids, and comets. But most sulphur previously found on Mars has been in the form of sulphate salt evaporites, which formed as lakes and other bodies of water dried out on the surface of the planet long ago.

On Earth, sulphur deposits typically take the form of sulphates (the oxidised form of the mineral) or sulphites (the reduced form) with elemental sulphur forming in sedimentary rocks through the actions of sulphur-reducing micro-organisms in anaerobic (i.e. oxygen free) environments, and in volcanic rocks by the reaction of gaseous hydrogen sulphide and sulphur dioxide. The geology of Gale Crater is dominated by sedimentary deposits, including evaporites, but is generally low in sulphates. 

It is possible that the Convict Lake rock is of volcanic origin, and reached the Gale Crater locality as ejecta. However, the images of the rock resemble the surrounding sedimentary rocks, making it more likely that it is local in origin. This makes it likely that the sulphur has been derived from an original sulphate source in some way, although this does not necessarily imply the presence of sulphur reducing micro-organisms, as in the oxygen-free atmosphere of Mars, abiotic reducing reactions impossible on Earth become far more likely.

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