The discussion and speculation around Mars have taken a new turn with new information last week that a sample collected by Nasa’s Perseverance Mars rover from an ancient dry riverbed in Jezero Crater could preserve evidence of ancient microbial life. Taken from a rock named ‘Cheyava Falls’ last year, the sample, called ‘Sapphire Canyon,’ contains potential biosignatures, according to a paper published in the journal Nature. A potential biosignature is a substance or structure that might have a biological origin but requires more data or further study before a conclusion can be reached about the absence or presence of life.
“The identification of a potential biosignature on the Red Planet is a groundbreaking discovery, and one that will advance our understanding of Mars,” said acting Nasa administrator Sean Duffy. Perseverance came upon Cheyava Falls in July 2024 while exploring the ‘Bright Angel’ formation, a set of rocky outcrops on the northern and southern edges of Neretva Vallis, an ancient river valley measuring 400m wide that was carved by water rushing into Jezero Crater long ago.
The rover’s science instruments found that the formation’s sedimentary rocks are composed of clay and silt, which, on Earth, are excellent preservers of past microbial life. They also are rich in organic carbon, sulphur, oxidised iron (rust), and phosphorous. “The combination of chemical compounds we found in the Bright Angel formation could have been a rich source of energy for microbial metabolisms,” said Perseverance scientist Joel Hurowitz of Stony Brook University, New York and lead author of the paper. “But just because we saw all these compelling chemical signatures in the data didn’t mean we had a potential biosignature. We needed to analyse what that data could mean.”
First to collect data on this rock were Perseverance’s PIXL (Planetary Instrument for X-ray Lithochemistry) and SHERLOC (Scanning Habitable Environments with Raman & Luminescence for Organics & Chemicals) instruments. While investigating Cheyava Falls, an arrowhead-shaped rock measuring 3.2ft by 2ft, they found what appeared to be colourful spots. The spots on the rock could have been left behind by microbial life if it had used the raw ingredients, the organic carbon, sulphur, and phosphorus, in the rock as an energy source.
In higher-resolution images, the instruments found a distinct pattern of minerals arranged into reaction fronts (points of contact where chemical and physical reactions occur) the team called leopard spots. The spots carried the signature of two iron-rich minerals: vivianite (hydrated iron phosphate) and greigite (iron sulphide). Vivianite is frequently found on Earth in sediments, peat bogs, and around decaying organic matter. Similarly, certain forms of microbial life on Earth can produce greigite.
The combination of these minerals, which appear to have formed by electron-transfer reactions between the sediment and organic matter, is a potential fingerprint for microbial life, which would use these reactions to produce energy for growth. The minerals also can be generated abiotically, or without the presence of life. Hence, there are ways to produce them without biological reactions, including sustained high temperatures, acidic conditions, and binding by organic compounds. However, the rocks at Bright Angel do not show evidence that they experienced high temperatures or acidic conditions, and it is unknown whether the organic compounds present would’ve been capable of catalysing the reaction at low temperatures.
The discovery was particularly surprising because it involves some of the youngest sedimentary rocks the mission has investigated. An earlier hypothesis assumed signs of ancient life would be confined to older rock formations. This finding suggests that Mars could have been habitable for a longer period or later in the planet’s history than previously thought, and that older rocks also might hold signs of life that are simply harder to detect.