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NASA’s Perseverance rover has found a rock riddled with what may be signs of ancient life. The rock, nicknamed “Cheyava Falls” after a famous waterfall in Arizona, shows hints that it could have supported living microbes billions of years ago – but for now, there is no way to be sure if life really existed there.

The rock measures about 1 metre by 0.6 metres and is mostly reddish, with thin veins of white calcium sulphate that probably formed when water flowed through fissures in the rock, depositing minerals in the cracks. Water is one of the ingredients necessary for life, but it wasn’t the only one that researchers found while poring over the Perseverance data.

They saw that between the streaks of white, there were strange light-coloured splotches, each just millimetres across and ringed with dark material containing iron and phosphate. “These spots are a big surprise,” said at the Queensland University of Technology in Australia in a NASA . “On Earth, these types of features in rocks are often associated with the fossilized record of microbes living in the subsurface.” That is because the type of chemical reaction that creates these sorts of leopard spots on Earth rocks can also provide useful energy for microbes.

In the same area where the rock is located, Perseverance also detected certain organic compounds that are often considered the building blocks of life. All of this together could be taken as a sign of bygone Martian microbes, but it is far from a smoking gun. “We should be cautiously enthused but pragmatically restrained,” says at Washington University in St. Louis, Missouri, who was not involved with this work. “For now, this is a sign of (probably) wet rocks undergoing chemical alteration.”

After all, there are ways to create all of these signatures without involvement from any living organisms at all. And there are some signs that the area may have once been flooded with hot magma, which could have prevented any life from surviving at the site.

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Unfortunately, it is unlikely that we will find out for sure whether Cheyava Falls has signs of life anytime soon. “We have zapped that rock with lasers and X-rays and imaged it literally day and night from just about every angle imaginable,” said at the California Institute of Technology in the press release. “Scientifically, Perseverance has nothing more to give.”

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The rover has added a sample of Cheyava Falls to its stash, which is designed to be brought back to Earth by a future mission. Once that happens, researchers will be able to use much more advanced instruments to study the sample in detail. “There really is no substitute for doing laboratory analyses on Earth,” says Byrne.

But NASA’s plans to return the Perseverance samples from Mars have been hit by a series of setbacks in the last year or so. It isn’t yet clear when – or whether – we might be able to look at this intriguing rock up close.