Giant String of Organic Molecules on Mars May Be One of the Best Signs of Life Yet

United Kingdom - 7dayes News Agency

Giant String of Organic Molecules on Mars May Be One of the Best Signs of Life Yet

A new NASA-led analysis concludes that it is "reasonable to hypothesize" that living things could have formed the odd organic molecules discovered on Mars. These long chains of hydrogen and carbon, found embedded within a sedimentary rock, cannot have their current abundance fully explained by nonbiological processes, opening the door to the possibility of ancient life on the Red Planet.

Scientists first reported the discovery of these organic molecules, known as alkanes, within a mudstone dubbed "Cumberland mudstone" in Mars' Yellowknife Bay region, a site of a former ancient lake. These molecules, with carbon chains ranging from 10 to 12 atoms long, were identified in March of last year. While shorter alkanes like methane and ethane are common and can form through abiotic processes, alkanes with 12 or more carbon atoms are considered more likely to be associated with biological processes.

Researchers conducted an in-depth analysis, employing mathematical modeling, data from the Curiosity rover, and recent radiolysis experiments. These investigations aimed to estimate the original quantity of these molecules billions of years ago when they were deposited in the rock. The study, published in the journal Astrobiology, found that the current abundance of alkanes in the sample ranges from 30 to 50 parts per billion (ppb). However, the rock has been exposed to Mars' harsh surface radiation for approximately 80 million years, leading to significant degradation of its organic content.

"Given the geologic history and thermal maturation of the organics preserved in the Cumberland sample, it is reasonable to presume that the recovered material is only a fraction (possibly several orders of magnitude less) of the primary lipid content that would have been entrained in the sedimentary unit when it was deposited two and a half billion years ago," the researchers explained in their paper. Using previous radiolysis experiments as a gauge, the researchers calculated a "conservative" initial abundance of 120 to 7,700 ppb for the alkanes, or the fatty acids from which they fragmented.

The team assessed multiple scenarios to explain the origin of these molecules. An extraterrestrial origin, such as interplanetary dust particles or meteorites, was ruled out because such particles cannot penetrate rock and there are no clear signs of meteorite impacts at the site. Organic molecules settling from the atmosphere were also discounted, as Mars' ancient atmosphere was not sufficiently hazy to account for the observed abundance. Water-rock interactions could produce organic molecules, but they typically yield smaller ones. The formation of fatty acids can also require high temperatures, which the Cumberland sample does not indicate.

Despite ruling out several theories, one nonbiological process remained plausible: researchers could not rule out that some of the organics formed abiotically in Mars' hydrothermal systems and were transported to the surface via watery, organic-rich fluids. However, the researchers stress that this does not constitute definitive proof of life. "To be clear, we do not claim that proof of ancient Martian life was found in the Cumberland mudstone," the researchers stated.

The Cumberland sample remains rich in many components typically associated with biological processes, including clay minerals that form in the presence of water, nitrates, a type of carbon linked to biological activity, and sulfur that helps preserve organic molecules. The Yellowknife Bay paleolake in Gale Crater held water for untold millions of years, ostensibly providing ample time for life-forming chemistry to occur. However, the Curiosity rover may have limitations in analyzing even larger molecules, which are more likely to be associated with biological processes, due to its method of separation and identification.

7dayes News Agency