The mystery of coal on Mars - What are the possible explanations

The rover has been roaming the neighboring planet since 2012, occasionally taking samples from its surface and doing on-site analyzes with its portable chemical laboratory.

1 18 09 08 57 8 carbon, ARIS, explanations, mystery

NASA's Curiosity rover has detected the signature of plenty of "light" carbon on Mars, for which there are three possible explanations: it came from chemical reactions in the atmosphere due to ultraviolet radiation, it was created by transient cloud or to have "local" biological origin, having been produced in the past by microbial life forms, as is the case on Earth.

The rover has been roaming the neighboring planet since 2012, occasionally taking samples from its surface and making on-site analyzes with its portable chemical laboratory. This time, the scientists, led by Professor of Geosciences Christopher House of Pennsylvania State University, who made the publication in the journal of the US National Academy of Sciences (PNAS), according to "Science", announced that Curi spectroscopically a signal that could be an indication of ancient Martian life, without of course excluding other more "minor" explanations.

The carbon found trapped in Martian rocks is impressively enriched with light carbon isotopes. On Earth such a signal is a strong indication of ancient microbial life. But since it is Mars - where initial estimates have been refuted from time to time - researchers are reluctant to celebrate. Thus, they study in parallel all the alternative non-biological interpretations of the phenomenon, mainly the effect of ultraviolet radiation on the atmosphere of the "red" planet and stardust. However, these alternative explanations are just as "exotic" as the possibility that some underground microbes once produced enriched carbon in the form of methane gas.

Carbon exists in two stable isotopic forms: "light" carbon-12, which is the vast majority of existing carbon, and heavier carbon-13. Life has evolved mechanisms on Earth that favor lighter carbon, with the result that most organic molecules of biological origin contain carbon-12.

The researchers analyzed the rover's measurements from 24 different rock samples from Gale Crater, which once contained an ancient lake. In six of these samples, the ratio of carbon-12 to carbon-13 was so high (much higher than on Earth) that House spoke of "dramatic signals." One possible plausible explanation is that billions of years ago germs fed carbon from magma into the Martian subsoil and then produced methane gas. Then, other surface germs would in turn feed on this methane, further enriching it with light carbon, which was eventually trapped in the rocks after the microorganisms died.

So far, however, the rover has not seen natural traces of ancient germs, so a modified version of the above theory is that after the initial stage of the process, which began with germs deep underground, the second stage on the planet's surface was not done by other germs, but from the ultraviolet radiation that may have decomposed the methane gas of microbial origin, thus enriching the light carbon.

Alternatively, UV radiation could have done all the "work" from scratch, without any help from the germs. This radiation, as shown by recent laboratory experiments on Earth by Japanese planetary scientists at the Tokyo Institute of Technology, can react chemically with carbon monoxide - which makes up 96% of the Martian atmosphere - and produce 12 highly enriched flowers.

Another alternative explanation is that, in the still young solar system, Mars passed through an interstellar molecular cloud of gas and dust, which is believed to occur every 100 million years. The carbon in interstellar dust is light and, judging by meteorite analyzes, could explain the increased levels of carbon-12 observed on Mars.

Curiosity continues to "smell" the current sparse Martian atmosphere and has already detected methane, but in very low concentrations to be able to measure carbon isotope levels. At the moment, it's hard to say which of the above scenarios - or perhaps another - is more valid.

House said with a resounding reservation that the new findings somewhat reinforce the possibility that microorganisms once existed on Mars, without ruling out the possibility that they still exist in its subsoil. He noted that "all three scenarios suggest an unusual carbon cycle on Mars, very different from anything on Earth today. But we need more data to decide what the right explanation is. "It would be nice if the rover could detect a large amount of methane and measure the carbon isotopes in it, but so far the amount of methane that has been detected is so small that the isotopes cannot be measured."