Curiosity Detects Carbon Signature That May Indicate Biological Activity in Mars

Carbon is essential for life. Based on that, a significant carbon signature found on the surface of Mars might suggest biological activity.

Search for Life

A substantial carbon signal is a good indication when looking for signs of life. It exists in all types of life that we are aware of.

However, there are several forms of carbon, which may accumulate in the environment for various reasons. Carbon fingerprints may not always imply the presence of life.

The number of protons in a carbon atom is always six, although neutrons might vary. Isotopes are carbon atoms with variable quantities of neutrons.

C12 and C13, both stable, and C14, radioactive, are the three carbon isotopes found in nature. Six neutrons make up C12, seven neutrons make up C13, and eight neutrons make up C14.

Carbon Isotopes

Life favors the carbon isotope C12 when it comes to carbon isotopes. It's used in photosynthesis and food metabolism. The rationale is straightforward.

Because C12 has one fewer neutron than C13, it forms fewer connections when it interacts with other atoms to form molecules than C13 does in the identical scenario.

Life is sluggish, and it will constantly look for the simplest solution. Because it makes fewer bonds than C13, C12 is easier to employ. It's less difficult to obtain than C13 because life never takes the difficult path when an easier path exists.

In Mars' Gale crater, the Curiosity rover is hard at work looking for evidence of life. It drills through the rock, removes a pulverized sample, and deposits it in its onboard chemical lab. SAM stands for Sample Analysis at Mars, and it is the name of Curiosity's lab.

The rover bakes the sample and converts the carbon in the rock into methane via pyrolysis within SAM. The pyrolysis is carried out in a stream of inert helium to avoid contamination.

The Tunable Laser Spectrometer is then used to probe the gas to determine which carbon isotopes are present in the methane.

Examining Samples

The SAM team at Curiosity utilized this method to evaluate 24 rock samples and discovered something fascinating. The C12/C13 ratios in six of the samples were unusually high.

The C12/C13 ratios in the samples from these six locations are more than 70 parts per thousand greater than an Earth-based reference standard. C12 makes up 98.93 percent of carbon on the planet, whereas C13 makes up the remaining 1.07 percent.

The findings were revealed in recent research published in the Proceedings of the National Academy of Sciences. The principal author is Christopher House, a Curiosity scientist from Penn State University. The paper's title is "Depleted carbon isotope compositions detected at Gale crater, Mars."

It's a fascinating discovery, and if the same findings were acquired on Earth, they would indicate that a living activity caused the abundance of C12.

Surface microorganisms created methane as a byproduct on early Earth. They're called methanogens, and they're Archaea domain prokaryotes. Methanogens may still be found today in anoxic wetlands, ruminant digestive systems, and severe conditions such as hot springs.

Needing Further Study

These bacteria create methane, which interacts with UV light and enters the atmosphere. These interactions result in more complex molecules, which rain down on the Earth's surface.

They, together with their carbon traces, are retained in Earth rocks. It's possible that something similar happened on Mars, which would explain Curiosity's results.

However, this is Mars. If there's one thing the history of the quest for life on Mars has taught us, it's not to get ahead of ourselves.

"We're discovering tantalizingly fascinating stuff on Mars," said Paul Mahaffy, former chief scientist for Curiosity's Sample Analysis at Mars lab. "But we'd need more proof to conclude we've detected life."

"There are several conceivable reasons for the anomalously reduced 13C discovered in evolved methane," the scientists write in their report, "but no single explanation can be accepted without more investigation."

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