Photo credit: science.nasa.gov
Recent analyses of crushed Martian rock by NASA’s Curiosity rover have unveiled the largest organic molecules found on Mars to date. This discovery, shared in a study published in the Proceedings of the National Academy of Sciences, indicates that prebiotic chemistry on Mars may have progressed further than scientists previously believed.
In their investigation, researchers examined a rock sample utilizing Curiosity’s Sample Analysis at Mars (SAM) mini-lab, identifying molecules such as decane, undecane, and dodecane—compounds composed of 10, 11, and 12 carbon atoms, respectively. These larger organic compounds are believed to be remnants of fatty acids integrated into the sample. On Earth, fatty acids serve as essential components for building life at the molecular level.
Fatty acids are produced by living organisms to form cell membranes and support various cellular functions. However, these acids can also arise through non-biological processes, such as geological reactions involving water and minerals in hydrothermal environments.
While the exact origins of the identified molecules remain uncertain, their detection has invigorated the Curiosity science team for several reasons.
Previously, Curiosity had detected smaller and simpler organic compounds on Mars, but the presence of these larger molecules marks a significant step toward demonstrating that organic chemistry on the planet might have achieved complexities associated with the potential for life.
Moreover, this research enhances the likelihood of finding significant organic molecules, referred to as “biosignatures,” which can be exclusively formed in the presence of life. This alleviates former worries about whether such compounds could survive millions of years of exposure to harsh Martian conditions, including intense radiation and oxidation.
The significance of this finding is also tied to future plans to return Martian samples to Earth for in-depth analysis using advanced instruments not available on the Martian surface.
“Our study demonstrates that we could detect no chemicals that suggest the existence of past life forms on Mars,” stated Caroline Freissinet, the principal author and a research scientist with the French National Centre for Scientific Research in Guyancourt.
In 2015, Freissinet co-led a team that was the first to identify organic molecules on Mars in the same sample, known as “Cumberland.” This sample has undergone multiple analyses with SAM utilizing varying methodologies.
Curiosity obtained the Cumberland sample from Yellowknife Bay, an area that appeared to resemble an ancient lakebed, during a drilling operation in May 2013. The rover was initially on a path toward Mount Sharp but was rerouted to this intriguing location due to its potential for revealing crucial historical data about Gale Crater, which is estimated to be around 3.7 billion years old.
The insights obtained from the Cumberland sample have previously indicated a wealth of clay minerals formed in aqueous environments, abundant sulfur conducive to organic molecule preservation, and high nitrate levels, essential for life on Earth. Additionally, traces of methane formed from a carbon type linked to biological processes have also been detected within the sample.
Most notably, the evidence confirming Yellowknife Bay was home to an ancient lake suggests that liquid water may have persisted in Gale Crater for millions, if not longer, providing ample opportunity for life-supporting chemistry to develop in these historical Martian environments.
The discovery of the recent organic compounds arose during a separate experiment aimed at detecting amino acids, which are vital for protein synthesis. While the team did not uncover evidence of amino acids, they identified small quantities of decane, undecane, and dodecane instead.
Scientists surmised that these molecules could be the result of larger compounds fragmented during the heating process. By retracing their steps, they theorized that these molecules originated from the fatty acids undecanoic acid, dodecanoic acid, and tridecanoic acid.
To validate their hypothesis, the researchers mixed undecanoic acid into a clay simulating Martian conditions and performed a SAM-like heating experiment, successfully producing decane. They referenced existing research to theorize that undecane could derive from dodecanoic acid, while dodecane could arise from tridecanoic acid.
An intriguing aspect of their study was the observation regarding the length of the carbon chains in the presumed fatty acids. Each fatty acid features a chain of 11 to 13 carbon atoms. It is noteworthy that typical non-biological processes generally produce shorter fatty acids, with fewer than 12 carbons.
Although it is possible that the longer-chain fatty acids exist within the Cumberland sample, the SAM apparatus is not tailored to detect extended carbon chains.
Ultimately, researchers acknowledge the limitations inherent in employing current Mars instruments for molecular analysis. “We are prepared to make the significant leap to bring Martian samples back to Earth, allowing us to conclusively address questions about the existence of life on Mars,” added Glavin.
This investigation was sponsored by NASA’s Mars Exploration Program, with the Curiosity mission being led by NASA’s Jet Propulsion Laboratory, managed by Caltech. SAM was constructed and tested at NASA’s Goddard Space Flight Center, with contributions from CNES, the French Space Agency, which provided part of the SAM subsystem.
Source
science.nasa.gov