An article published in the journal “Proceedings of the National Academy of Sciences” reports the detection of samples rich in carbon-12, which on Earth is associated with biological processes, in Gale crater on Mars by NASA’s Mars Rover Curiosity. A team of researchers used the TLS instrument, part of Curiosity’s SAM mini-laboratory, to analyze the samples to check the amount of isotopes as well. The result is a limited presence in some samples of carbon-13 compared to that detectable in the atmosphere and in Martian meteorites. On Earth, such a result indicates that the sample was produced by some biological process. However, the researchers also offered alternative explanations related to non-biological processes.
On Earth, carbon isotope analysis is a method of looking for traces of biological processes because carbon-12 is lighter and has weaker chemical bonds than carbon-13 resulting in it reacting more quickly in biological processes. The consequence is that organic materials tend to be high in carbon-12 and low in carbon-13.
On Mars, the situation regarding carbon isotopes could be very different since there are only hypotheses concerning the presence, today or in the past, of life forms. This situation must be verified therefore this study is based on the analysis of 24 samples collected by the Mars Rover Curiosity in various areas of Gale crater, where it landed on August 6, 2012, such as the Stimson formation shown in the image. Some research brought evidence that, in very ancient times, that crater went through periods when it was a lake, so it’s a place where it makes sense to try to verify the hypothesis of the presence of life forms.
Over the years, the Mars Rover Curiosity has explored various areas of Gale Crater taking several samples. The TLS (Tunable Laser Spectrometer) instrument of the SAM (Sample Analysis at Mars) mini-laboratory was used to analyze the isotopic composition of the carbon contained in 24 samples. The ratio of carbon-12 to carbon-13 varied widely in different samples, and nearly half of those samples have lower carbon-13 content than can be detected in the Martian atmosphere and meteorites. However, this result is only the beginning of the research.
Carbon cycles are well known on Earth but scientists have only just started understanding the Martian ones. This means that each result must be assessed very carefully based on objective findings. For this reason, it’s not possible to claim that the results of the carbon isotope analysis in the 24 samples indicate the presence, today or in the past, of life forms. The researchers are the first to have offered some alternative explanations.
One of the possible non-biological origins of the carbon isotope anomalies is an interaction between ultraviolet solar emissions and carbon dioxide from the Martian atmosphere, which may have produced new molecules that would have deposited on the surface of Mars. The other possible non-biological origin of the anomaly is a very rare event dating back hundreds of millions of years with the passage of the solar system through a molecular cloud rich in carbon-12.
The problem is that scientists still have limited data on Mars, so the origin of the anomaly as a consequence of the activity of ancient bacteria fits the data as much as alternative explanations. The ancient bacteria hypothesis is linked to the production of methane, a compound that is occasionally detected on Mars. Again, there are possible explanations related to life forms and others related to non-biological processes. After decades of Martian missions, only very small areas of the red planet have been explored and only the most recent missions include instruments capable of searching for traces of life. The search is still long and could still offer many surprises.