On the prowl at Vera Rubin ridge Credit: NASA/JPL-Caltech/MSSS

Research carried out by NASA’s Curiosity rover at Gale Crater point to the possible ultraviolet degradation of biologically produced methane.

The robot has permitted scientists to analyze carbon isotopes in sediment samples taken from half a dozen exposed locations, including an exposed cliff.

According to a just-published paper led by Christopher House, professor of geosciences at the Pennsylvania State University, researchers single out three plausible explanations for the carbon’s origin: cosmic dust, ultraviolet degradation of carbon dioxide, or ultraviolet degradation of biologically produced methane.

The researchers note in a new issue of the Proceedings of the National Academy of Sciences that: “All three of these scenarios are unconventional, unlike processes common on Earth.”

That third possible method of producing carbon-13 depleted samples has a biological basis.

Credit: NASA

Unusual carbon cycle

According to a Penn State research story, here on Earth, a strongly carbon-13 depleted signature from a paleosurface would indicate past microbes consumed microbially produced methane.

“Ancient Mars may have had large plumes of methane being released from the subsurface where methane production would have been energetically favorable. Then, the released methane would either be consumed by surface microbes or react with ultraviolet light and be deposited directly on the surface,” the research statement explains.

“However, according to the researchers, there is currently no sedimentary evidence of surface microbes on the past Mars landscape, and so the biological explanation highlighted in the paper relies on ultraviolet light to place the carbon-13 signal onto the ground,” the statement continues.

The image shows the Highfield drill hole on Vera Rubin Ridge. Drill powder from this hole showed carbon isotope values indicating a carbon cycle that includes either subsurface life, intense UV radiation penetrating the atmosphere, or Interstellar dust. The image was taken by the Mars Hand Lens Imager on sol 2247. Credit: NASA/Caltech-JPL/MSSS via Penn State.

“All three possibilities point to an unusual carbon cycle unlike anything on Earth today,” said House. “But we need more data to figure out which of these is the correct explanation. It would be nice if the rover would detect a large methane plume and measure the carbon isotopes from that, but while there are methane plumes, most are small, and no rover has sampled one large enough for the isotopes to be measured.”

House says that finding the remains of microbial mats or evidence of glacial deposits could also help clear things up. “We are being cautious with our interpretation, which is the best course when studying another world.”

To read the full research statement from Penn State, written by the university’s A’ndrea Elyse Messer, go to:

https://www.psu.edu/news/research/story/newly-discovered-carbon-may-yield-clues-ancient-mars

Also, go to Paul Voosen’s Science magazine article — “Mars rover detects carbon signature that hints at past life source Dramatically “light” carbon could also be explained by atmospheric reactions or cosmic dust” at:

https://www.science.org/content/article/mars-rover-detects-carbon-signature-hints-past-life-source?

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