But there are different types of carbon, and carbon can become concentrated in the environment for other reasons.
Three carbon isotopes occur naturally: C12 and C13, which are stable, and C14, a radionuclide.
C12 has one fewer neutron than C13, which means that when it bonds with other atoms into molecules, it makes fewer connections than C13 does in the same situation.
Then it probes the gas with an instrument named the Tunable Laser Spectrometer to find out what carbon isotopes are in the methane.
Compared to an Earth-based reference standard for C12/C13 ratios, the samples from these six sites contained greater than 70 parts per thousand more C12.
A new study published in the Proceedings of the National Academy of Sciences presented the findings.
Methanogens are still present today on Earth, in anoxic wetlands, in the digestive tracts of ruminants, and extreme environments like hot springs.
The same thing might have happened on Mars, and if it did, it could account for Curiosity’s findings.
So when it comes to this newly-detected carbon signature on Mars, scientists can find it challenging to keep their minds open to new possibilities that may not exist on Mars.
“The hardest thing is letting go of Earth and letting go of that bias that we have and really trying to get into the fundamentals of the chemistry, physics and environmental processes on Mars,” said Goddard astrobiologist Jennifer L.
Molecular clouds are primarily molecular hydrogen, but one may have been rich in the type of lighter carbon detected by Curiosity in Gale Crater.
The hypothesis fits since Curiosity found some of the elevated C12 levels at the tops of ridges—such as the top of Vera Rubin Ridge—and other high points in Gale Crater.
Mars’ atmosphere is over 95% carbon dioxide, and in this scenario, UV light would’ve interacted with carbon dioxide gas in Mars’ atmosphere producing new carbon-containing molecules.
The samples came from five locations in Gale Crater, and all the locations had one thing in common: they have ancient, well-preserved surfaces.
As Paul Mahaffy said, the findings are “tantalizingly interesting.” But scientists are still learning about Mars’ carbon cycle, and there’s a lot we’re still ignorant about.
Ideally, it would encounter another methane plume and sample it, but those events are unpredictable, and there’s no way to prepare for one.