Curiosity finds evidence that Mars may have harbored life in ancient times

Until recently, neither orbiters nor rovers had found direct evidence of the carbon cycle on Mars. Finding it would mean that CO₂ levels in the planet’s atmosphere could have been maintained at levels that would have provided suitable conditions for the emergence and existence of biological life. A new analysis of spectroscopic data from the Curiosity rover has found such evidence for the first time, bolstering the case for life on ancient Mars.

A panorama of Gale Crater, where the rover first discovered traces of carbonates. Image Credit: NASA

In 2022 and 2023, NASA’s Curiosity rover explored the floor of Gale Crater. A team of scientists reanalyzed the data collected by the rover on four cores from different parts of the crater. In three samples, the presence of the mineral siderite was recorded for the first time. This mineral is formed when rock binds atmospheric carbon dioxide. This is the first evidence of the carbon cycle on ancient Mars. Volcanoes emitted CO₂ into the atmosphere, the gas accumulated in it, partly evaporated into space, and partly bound to the rock – returned to the bowels of the planet.

The circulation of carbon dioxide on Mars would have created conditions for its heating and, therefore, an environment potentially suitable for life. Evidence of liquid water at that time – about 3.5 billion years ago – has already been found and is considered highly reliable. The discovery of signs of a carbon cycle at the same time period indicates the presence of suitable temperature conditions, which together increases the likelihood of life on prehistoric Mars.

In addition, scientists have answered the question of why siderite, a mineral consisting of iron and carbon trioxide with a small amount of magnesium, was not detected earlier. It was most likely masked by a signal from magnesium sulfate, which is widespread on the surface of Mars.

«It turns out that the presence of other minerals — particularly highly water-soluble magnesium sulfate salts — likely masks the presence of carbonate minerals in the orbital data. Since similar rocks containing these salts have been found all over the planet, we conclude that they also likely contain large amounts of carbonate minerals,” the scientists explained.

The researchers promise to review all information regarding the detection of magnesium compounds on Mars. If the widespread presence of siderite is confirmed, this will be the basis for revising the climate models of Mars – in particular, taking into account the carbon cycle and a new assessment of the evolution of the Red Planet.