For the past four years, the Perseverance rover has been exploring the surface of Mars, aiming to understand the geology of Jezero crater and to collect well-chosen rock samples for potential return to Earth. After studying the igneous rocks at the crater floor and the sedimentary deposits of an ancient delta above them, the rover climbed the crater’s rim. It was there that a series of rocks with highly unusual chemical and mineralogical compositions were found. These rocks bear witness to water-rock interactions dating back to the very early history of Mars.

This discovery was made by an international scientific team using the SuperCam instrument suite^[1]. SuperCam identified rocks exceptionally rich in silica, composed of different forms of silica: opal (known on Earth for its iridescent properties), chalcedony (a form of quartz with very fine crystals), and perfectly crystallized quartz. While quartz is common in Earth's crust, this is the first time this mineral has been directly identified on the Martian surface, thanks to Raman spectroscopy deployed by SuperCam. The dissolution and precipitation of silica suggest the possible existence of hydrothermal processes, which are frequent on Earth near impact crater rims. The energy released by crater formation and the associated deformation provide heat, promoting fluid circulation within fractured rocks.

These rocks thus provide evidence of very ancient water circulation on Mars and are of great interest from an exobiological perspective. Siliceous rocks, particularly opal, have remarkable capabilities for preserving traces of life, whether morphological or molecular. If Perseverance succeeds in sampling these types of rocks, they will be prime targets for searching for biosignatures once returned to Earth.

“With this publication, we demonstrate the presence of different silica phases, and for the first time from the Martian surface, we identify an ‘iconic’ mineral, quartz, with the most well-defined Raman spectrum ever measured beyond Earth—nearly 100 years after the technique’s discovery. We also detected other forms of silica: opal and chalcedony. All of this highlights a very ancient hydrothermal system, and these rocks are particularly interesting from an exobiology perspective because silica is highly effective at preserving signatures of living organisms,” explains Pierre Beck, professor at Université Grenoble Alpes (UGA) conducting his research at IPAG.

“Observing traces of an ancient hydrothermal system linked to an impact crater on the Martian surface is particularly remarkable, as hydrothermal environments are among the primary targets in the search for microbial life in the Solar System. Mars’ surface is covered in impact craters, making it highly likely that similar environments were once common on the Red Planet,” adds Lucia Mandon, postdoctoral researcher at the French National Centre for Space Studies (CNES), also conducting research at IPAG.

^[1] This highly innovative instrumental suite was jointly developed by a consortium of French laboratories led by IRAP (Toulouse, France), LANL (Los Alamos, USA), with a contribution from the University of Valladolid (Valladolid, Spain). CNES is responsible for the French contribution to SuperCam on behalf of NASA. CNES, CNRS, and numerous universities provided human resources for the development of this instrument, which is operated alternately by the European team through the control center at CNES in Toulouse (FOCSE Mars 2020) and by the American team from LANL