NASA investigates ‘unusual’ carbon footprints on Mars

Among the possibilities before this finding is that of biological life in the past of Mars , but it is not the only hypothesis.

The analysis of the sediments collected by NASA  ‘s Curiosity rover  in the Gale Crater on Mars  has helped scientists refine the possible origin of carbon on the red planet and try to get a little closer to its unknown past.

After analyzing carbon isotopes from samples taken by the rover at half a dozen locations in the crater, scientists have narrowed down the plausible explanations for the carbon ‘s origin to three : cosmic dust, carbon dioxide degradation caused by ultraviolet radiation, or ultraviolet degradation of biologically produced methane.

In an article published in the journal Proceedings of the National Academy of Sciences (PNAS), the authors who pose these three scenarios also conclude that all three are “unconventional” compared to processes on Earth.

What are we talking about?

Since August 2012, Curiosity has been roaming Gale Crater sampling layers of ancient rock, and sending the results home for interpretation.

Carbon has two stable isotopes, 12 and 13. Measuring the amounts of each in a substance can help determine the carbon cycle and find out details about what it was like, even if it happened long ago.

To obtain the samples, Curiosity drilled into the ancient rock surface, retrieved samples from buried sedimentary layers, and heated them to separate the chemicals.

The carbon produced by this pyrolysis showed a wide range of carbon-12 and carbon-13 amounts, depending on where or when the sample had formed. Some of the carbon was exceptionally carbon -13 depleted while other samples had been enriched .

“The samples extremely depleted in carbon 13 are similar to those taken in Australia from sediments that were 2.7 billion years old,” explains Christopher H. House, a researcher at the University of Pennsylvania (USA).

“Those samples were caused by biological activity when methane was consumed by ancient microbial mats, but we can’t necessarily say that on Mars because on that planet they may have formed from different materials and processes than on Earth ,” he says. the investigator.

To explain such exceptionally depleted samples, the authors suggest three possibilities: a cosmic dust cloud, ultraviolet radiation that breaks down carbon dioxide, or ultraviolet degradation of biologically created methane.

According to House, every two hundred million years the solar system passes through a galactic molecular cloud, but “it doesn’t lay down much dust”, so “it’s hard to see any of these depositional events in Earth’s record”.

To generate enough of a layer for Curiosity to take samples, the galactic dust cloud would have had to lower the temperature on a Mars that still contained water and spawned glaciers.

The dust would have settled on the ice and then had to remain in place when the glacier melted, leaving behind a layer of debris that included carbon , a “plausible” explanation that requires further study, the authors say.

Another explanation for lower amounts of carbon 13 is the ultraviolet conversion of carbon dioxide to organic compounds such as formaldehyde, but this, too, requires further study to confirm or rule it out.

Old life?

The third possibility has a biological basis: On Earth, a strongly carbon -13-depleted signature of a paleosurface would indicate that past microbes consumed microbially produced methane.

Ancient Mars may have had large plumes of methane released from underground and, once outside, either consumed by surface microbes or reacted with ultraviolet light and deposited directly on the surface.

However, according to the researchers, there is currently no sedimentary evidence of surface microbes in the past landscape of Mars .

“All three possibilities point to an unusual carbon cycle that is unlike anything on Earth today,” but “we need more data to determine which of these is the correct explanation,” insists House.

Curiosity is still collecting and analyzing samples and will return to the location where it found some of the samples for this study in about a month.

Another article published today in PNAS raises the possibility that 3 billion years ago Mars had the conditions for a cold and wet climate.

The study, conducted by researchers at Université Paris-Saclay based on simulations, posits that Mars may have supported an ocean in the northern lowland basin that may have been stable even at below-freezing global mean surface temperatures. . EFE