Martian Mudstone Evidence from the Perseverance Rover Is a Potential Biosignature

An image of the rock named "Cheyava Falls" in the "Bright Angel formation" in Jezero crater, Mars collected by the WATSON camera onboard the Mars 2020 Perseverance rover. The image shows a rust-colored, organic matter bearing sedimentary mudstone sandwiched between bright white layers of another composition. The small dark blue/green to black colored nodules and ring-shaped reaction fronts that have dark rims, and bleached interiors are proposed to be potential biosignatures. Image credit: NASA/JPL-Caltech/MSSS.

Data and images from NASA's Mars Perseverance rover reveals that recently discovered rocks in the Jezero crater are organic carbon bearing mudstones.

The findings, detailed in a paper published in Nature, indicate that these mudstones experienced chemical processes that left behind colorful, enigmatic textures in the rock that represent potential biosignatures.

The paper, led by Joel Hurowitz, associate professor in the Department of Geosciences at Stony Brook University, builds upon ongoing research conducted with the rover since it landed in 2021 - work aimed at characterizing early Martian geological processes and collecting samples that may someday be returned to Earth.

Upon entering the Jezero crater's western edge, Perseverance investigated distinctive mudstone outcrops of the Bright Angel formation. There, the Mars 2020 science team conducted a detailed geological, petrographic, and geochemical survey of these rocks and found traces of carbon matter along with minerals, namely ferrous iron phosphate and iron sulfide.

While the research team is not claiming to have found some form of fossilized life on Mars, they do believe the rocks contain features that could have been formed by life, a potential biosignature. A potential biosignature is any characteristic, element, molecule, substance, or feature that could have been formed by past biological life, but which also could have formed in the absence of life. While a compelling find, the team points out that more data is needed before any conclusion can be made about whether microbial activity is responsible for the development of the features observed in the mudstones.

"These mudstones provide information about Mars' surface environmental conditions at a time hundreds of millions of years after the planet formed, and thus they can be seen as a great record of the planetary environment and habitability during that period," said Hurowitz, who has been involved with Mars rover research since he was a graduate student at Stony Brook University in 2004.

"We will need to conduct broader research into both living and non-living processes that will help us to better understand the conditions under which the collection of minerals and organic phases in the Bright Angel formation were formed," he added.

More specifically, the researchers concluded the following during their analyses:

• The organic carbon detected appears to have participated in post-depositional redox reactions that produced the observed iron phosphate and iron sulfide minerals. And these reactions occurred in a sedimentary rock environment at low temperature. Redox reactions are a type of chemical reaction that all living things derive energy from, and in low temperature sedimentary environments on Earth, these redox reactions are commonly driven by microbial life.
• A review of the various pathways by which redox reactions that involve organic matter can produce the observed suite of iron, sulfur, and phosphorus-bearing minerals reveals that both abiotic (physical not biological) and biological processes can explain the unique features observed in the Bright Angel formation.
• Their observations in the Bright Angel formation challenge some aspects of a purely abiotic explanation, and thus the researchers suggest that the iron and sulfur and phosphorus-bearing nodules and reaction fronts should be considered a potential biosignature.

Continued research will be done to assess the rocks and mudstone features. For the time being the researchers, ultimately, "conclude that analysis of the core sample collected from this unit using high-sensitivity instrumentation on Earth will enable the measurements required to determine the origin of the minerals, organics and textures it contains."