👽 Mars rover finds potential traces of ancient life

• NASA's rover Perseverance has collected a sample from Jezero Crater that may contain evidence of ancient microbial life on Mars.
• The sample comes from a rock containing organic carbon, sulfur, and phosphorus that could have provided energy to microorganisms.
• The discovery was made in younger sedimentary rocks than expected, suggesting Mars was habitable for a longer period.

Sample from ancient riverbed

NASA's rover Perseverance has collected a sample from an ancient dry riverbed in Jezero Crater that could preserve evidence of ancient microbial life. The sample was taken from a rock called "Cheyava Falls" last year and has been named "Sapphire Canyon". According to a study published in the journal Nature, the sample contains potential biosignatures.

A potential biosignature is a substance or structure that might have biological origin but requires more data before conclusions can be drawn about the presence or absence of life.

Rich chemical composition

The rover's scientific instruments found that the formation's sedimentary rocks consist of clay and silt, which on Earth are excellent preservers of past microbial life. The rocks are also rich in organic carbon, sulfur, oxidized iron, and phosphorus.

The combination of chemical compounds found in the Bright Angel formation could have been a rich energy source for microbial metabolisms. Although all these compelling chemical signatures were present in the data, additional analysis was required to understand what the results could mean for identifying a potential biosignature.

Leopard spots reveal minerals

Perseverance investigated Cheyava Falls, an arrowhead-shaped rock measuring 1 meter by 0.6 meters. The PIXL and SHERLOC instruments found colorful spots on the rock. The spots could have been left behind by microbial life if it had used the raw ingredients - the organic carbon, sulfur, and phosphorus - in the rock as an energy source.

In high-resolution images, the instruments found a distinct pattern of minerals arranged into reaction fronts that the team called leopard spots. The spots carried the signature of two iron-rich minerals: vivianite and greigite. Vivianite is frequently found on Earth in sediments, peat bogs, and around decaying organic matter. Certain forms of microbial life on Earth can produce greigite.

Electron transfer reactions

The combination of these minerals, which appear to have formed through electron transfer reactions between the sediment and organic matter, is a potential fingerprint for microbial life. Such life would use these reactions to produce energy for growth.

The minerals can also be generated abiotically, meaning without the presence of life. 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.

Younger rocks than expected

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.

Sapphire Canyon is one of 27 rock cores the rover has collected since landing at Jezero Crater in February 2021. Perseverance is exploring the "Bright Angel" formation, a set of rocky outcrops on the northern and southern edges of Neretva Vallis, an ancient river valley measuring 400 meters wide that was carved by water rushing into Jezero Crater long ago.

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