On Mars: Discovery of sulfur and an “interesting” rock that may have come into contact with ancient microbes – Libération

NASA is detailing two recent discoveries by its Curiosity and Perseverance rovers: unexpected deposits of pure sulfur crystals and a rock with “leopard spots,” which may be a sign of biological activity billions of years ago.

Great discoveries continue on the Red Planet, where two NASA rovers are currently traveling. The larger one, Curiosity, stumbled upon a fascinating sulfur deposit, while its smaller sibling, Perseverance, discovered a rock that may have harbored microbes billions of years ago.

Sulfur in its purest form

The Curiosity rover arrived on Mars in the summer of 2012. Travel 32 km With its wheels increasingly damaged by the terrain, it slowly climbs the base. Mount Sharp (5500 meters above sea level). The chemical composition of the soil changes over time. “Since October, the rover has been exploring a region of Mars rich in sulfates, a type of salt containing sulfur that forms when water evaporates.” NASA's Jet Propulsion Laboratory (JPL)—its center for robotic space missions—explains: In a blog postBut planetary scientists who follow its journey day after day did not expect that it would encounter a reserve of pure sulfur.

On May 30, Curiosity flipped over a rock that had collapsed under its own weight. The rover snapped a photo of the hollow, brittle wreckage… revealing a pile of bright yellow crystals.

“Finding pure sulfur crystals is like finding an oasis in the desert.” Ashwin Vasavada, Curiosity team scientist at JPL, is delighted. “In theory, it shouldn’t be there, so now we have to explain its existence. It’s these kinds of unexpected discoveries that make planetary exploration so exciting. The blog post specifies that pure sulfur can only form under certain, very restrictive conditions, and that until now we have never imagined these possible conditions in this area of ​​Mount Sharp. Along with the beautiful picture, there is a whole chapter of geological history to write.

The team of researchers analyzing Curiosity’s data is keenly interested in the piles of rock debris surrounding the rover. What kind of landslide scattered the rocks in the area, and what caused it? The latest findings suggest two scenarios: Some of the eroded, rounded rocks were dumped here by violent rivers 4 billion years ago, while others, more angular, may be the result of glacial avalanches.

Leopard spots, a breeding ground for microbes?

3,700 kilometers away, Perseverance is doing the same work as Curiosity, a Martian geologist, since early 2021, and it’s almost a twin. The American rover, which is the size of a car and weighs a ton, is advancing through the Neretva Gorge, an ancient riverbed that flowed into the Jezero Crater billions of years ago. This delta is full of promise: if the ancient lake that filled the crater, 250 meters deep, harbors some aquatic bacteria, we might be able to find traces of these microorganisms in the sediments.

With this in mind, Perseverance has just found a little treasure: a rock with “leopard spots,” mysteriously circular in outline and lighter in the middle, which may have been formed through a biological process. “These sites are a big surprise.” Witness on NASA website Astrobiologist David Flannery, who works on the mission from Queensland University of Technology, Australia. Because, “On Earth, these types of marks on rocks are often associated with the presence of fossils of microbes that lived beneath the surface.”

The stains are created by a chemical reaction involving hematite, an iron oxide that gives the rock its red color. The reaction releases iron and phosphate, creating the dark circles on the stone. It can be used as an energy source by microbes in the rock. But other scenarios are also possible, without the microbes.

Another amazing aspect of the rock is that it contains olivine crystals about a millimeter across. A mineral normally found in cooling magma… We can then imagine that the olivine was formed high up in the valley, at extremely high temperatures, and that this process, completely independent of any living organism, created the leopard's spots.

Organic molecules and water

The famous rock is one metre by 60 centimetres in size, and was named “Chiava Falls” after a waterfall in the Grand Canyon in the United States. “This is the most interesting, complex and important rock Perseverance has studied to date.” Ken Farley, a mission researcher at Caltech in California, summarizes. “On the one hand, this is our first irrefutable discovery of organic material, we have colored spots that indicate chemical reactions that may have served as an energy source for microbial life, and we have evidence that water—essential for life—has once passed through the rock. On the other hand, we are unable to pinpoint exactly how the rock formed.

And it’s not for lack of trying. Several scientific instruments from Perseverance were used to conduct the investigation. “Sherlock,” a spectrometer mounted at the end of its articulated arm, scanned the rock’s chemical composition and concluded that it contained organic molecules, that is, carbon-based. These are the building blocks of living things… and their presence is essential for the development of life, but the reverse is not true: an organic molecule is not necessarily involved in a biological process.

Sample return is not confirmed.

“We’ve been shining lasers and X-rays on this rock, photographing it day and night from every angle imaginable. Perseverance has nothing more to offer us.” Ken Farley warns. The rover even took a sample from Chiava Falls on July 21, placing it in a carefully sealed tube that it carries with it, along with 21 other samples collected so far. For Farley, the next step is clear: “To understand what happened in this Martian valley billions of years ago, we must return the sample to Earth to study it with the advanced tools available in the laboratory.”

Unfortunately, this is not a win-win. The latest news is that the sample return mission as envisioned by NASA and ESA was deemed too expensive and was rejected. A call for proposals has been opened and NASA is currently looking for a less expensive solution to recover at least part of the pipe. The Chiava Falls rock will keep its secrets for a few more years.