NASA’s Curiosity rover collected a series of soil samples from Mars in which a carbon isotope associated with biological processes on Earth is particularly abundant. The researchers involved have now made this public. While possible life forms would explain the find, they also found two processes that do not require life forms and also fit the data. Nevertheless, they speak of a fascinating find, which, however, requires further analysis in order to be able to rule out the non-biological processes.
Non-biological enrichment possible
Like the research team led by Christopher House from Pennsylvania State University now explained, their analysis is about 12C, one of two stable isotopes of carbon, the building block of life on earth. This isotope is by far the most common on Earth, 13C comes only to one percent. In half of the soil samples analyzed, Curiosity now has significantly more 12C found than would be expected given the composition of the atmosphere and Martian meteorites.
But while that would indicate life on Earth, that is not necessarily the case on Mars. Precisely because much of the carbon cycle on Earth involves life, we know comparatively little about non-biological processes involving carbon such as might exist on Mars, the team writes. That’s why the proof is exciting, but not proof of life.
It is possible that the characteristic signature that Curiosity found goes back to bacteria that produced methane a long time ago, which was converted in the atmosphere and fell back to the surface. But it could also be based on carbon dioxide gas that has been non-biologically altered by UV light. It is even conceivable that the material came from a gigantic cloud of matter through which the solar system raced a long time ago.
Currently, the carbon cycle on Mars is not understood enough to favor one of the hypotheses. In order to find out whether the signature goes back to life, further analyzes are necessary. The researchers will present their find and the various possible explanations in the next issue of the Proceedings of the National Academy of Sciences.