NASA’s Curiosity rover found on Mars the longest molecules ever discovered on this planet, which may indicate evidence of ancient life.
According to the study, published on March 24 in the scientific journal Proceedings of the National Academy of Sciences, chains of molecules containing up to 12 interconnected carbon atoms were found in rock samples is 3.7 billion years old. The samples were collected by Curiosity at the bottom of a dried-up Martian lake in «Yellowknife Bay».
According to the researchers, these long carbon chains are derived from fatty acids, which are produced by living things on Earth during the formation of cell membranes and perform other functions. These fatty acids can be formed without the participation of living organisms in the process of chemical reactions under the influence of various geological processes. The main focus of the research is on the interaction of water with minerals in hydrothermal springs.
«The fact that fragile linear molecules are still present on the surface of Mars 3.7 billion years after their formation allows us to make a new claim: If life ever appeared on Mars billions of years ago, at the same time as life appeared on Earth, chemical traces of this ancient life may still be present today for us to detect», — said Caroline Fraisinet, co-author of the study and an analytical chemist at the French National Center for Scientific Research in the United States.
According to the results study of rock samples in the Curiosity Sample Analysis at Mars mini-laboratory, the molecules decane, undecane, and dodecane — compounds consisting of 10, 11, and 12 carbon atoms were detected. Curiosity has been operating on Mars since 2012 in the 154 km wide Gale Crater area. This crater was formed as a result of a collision between the Red Planet and an ancient meteorite. Since then, the rover has already traveled more than 30 km, exploring «Yellowknife Bay» and Mount «Sharp», a 5.5 km high mountain located in the center of the crater.
The molecules were found in a drilled rock sample called «Cumberland». Curiosity found it back in 2013. Since then, this sample has been repeatedly studied by scientists. Preliminary analyzes have shown that it is rich in clay minerals, sulfur and nitrates.
Nevertheless, for more than 10 years, researchers could not detect hydrocarbon molecules in this sample. They were eventually identified by chance when scientists were searching for amino acids.
The scientists tested the new method by preheating the sample to 1.1 thousand degrees Celsius in an effort to release oxygen before starting the research. Their results did not confirm the presence of amino acids, but they did detect fatty molecules.
According to the scientists, these molecules may be residues of fatty acids, also called undecanoic, dodecanoic, and tridecanoic acids. Fatty acids are long chains of carbon and hydrogen with a carboxylic (-COOH) acid group at the end.
To test this, the researchers mixed undecanoic acid with Martian clay and heated it. After heating, the undecanoic acid released the decane, as predicted. The researchers then referred to experiments already published by other scientists to show that undecane could separate from dodecanoic acid and dodecane — from tridecanoic acid. The backbone of each fatty acid is a long straight chain of 11-13 carbon atoms, depending on the molecule. It is noteworthy that non-biological processes typically produce shorter fatty acids with fewer than 12 carbon atoms.
«There is evidence that liquid water has existed in Gale Crater for millions of years and probably much longer, meaning there was plenty of time for vital chemical processes to form in these crater-lake environments on Mars. We’re ready to take the next big step and bring samples from Mars back to Earth, to our laboratories, to resolve the debate about life on the Red Planet», — said Daniel Glavin, senior sample return scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, and study co-author.
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