(ORDO NEWS) — NASA’s Curiosity Mars rover landed on the surface of Mars on August 6, 2012, and has since traveled along the floor of Gale Crater, collecting samples and sending scientific data back to Earth.
Analysis of carbon isotopes in sedimentary rock samples collected at several points of exposure of rock layers to the surface, led the researchers to suggest three possible scenarios for the origin of carbon – space dust, degradation of carbon dioxide by ultraviolet (UV) radiation, or degradation by UV radiation of biologically produced methane.
Carbon has two stable isotopes, carbon-12 and 13. By comparing the relative amounts of these isotopes in different samples, one can get an idea of the carbon cycle, even if it took place many years ago.
Spectrographic analysis of a portion of reduced carbon obtained by pyrolysis of the sample in a special chamber of the onboard analyzer of the Curiosity rover showed a wide range of different ratios between C12 and C13, depending on the place of origin of the sample under study. Some samples were very depleted in the isotope C13, while other samples, on the contrary, were enriched in this heavier nuclide.
To explain the composition of the extremely carbon-13 depleted samples, the researchers proposed three possibilities. According to the first scenario, ancient Mars fell into a cloud of cosmic dust, which lowered the temperature on the planet, on the surface of which there was already water by that time, and formed glaciers.
The dust then settled on the surface of the glacier and remained there until the glacier melted, leaving a layer of dirt, including carbon, on the surface. However, until now, scientists have not found enough convincing evidence of the presence of glaciers in Gale Crater. Therefore, this explanation seems possible, but not the most probable.
According to the second explanation, the reduced amounts of C13 are due to the conversion of carbon dioxide to organic compounds, such as formaldehyde, in the presence of UV radiation. A number of studies have shown that this process can lead to carbon isotope fractionation, but the authors point out the need for more detailed experiments of this kind.
A third possible method for obtaining a carbon-13 depleted sample has a biological basis. On Earth, the depletion of carbon samples in the isotope C13 points to microbial uptake of biologically produced methane in the past.
On ancient Mars, the presence of large jets of methane beating from under the surface is not ruled out. The released methane could then either be absorbed by microbes that lived on the surface of the planet, or react with UV radiation and then be deposited directly on the surface.
However, according to the authors, there is currently no evidence for the presence of microbes on the surface of ancient Mars, and therefore the biological origin noted in the work is rather associated with reactions of methane under the action of UV radiation.
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