The Mars rover Curiosity has measured the largest organic molecules ever found on Mars in the rocks of an ancient seabed. In the drill sample nicknamed "Cumberland", a team led by Caroline Freissinet from Sorbonne Université discovered the alkanes decane, undecane and dodecane, simple carbon chains consisting of ten, eleven and twelve carbon atoms, which are occupied by hydrogen atoms. As the research group reports in the scientific journal "PNAS", they used a modified measurement method that was optimised for larger molecules. The molecules discovered are not themselves evidence of past life on Mars. However, the discovery gives hope that the probe can also find more complex substances that provide more information about the chemistry of early Mars.
The team used the "Sample Analysis at Mars" (SAM) instrument platform, whose three instruments can measure and identify organic substances released from the sample. Depending on how the sample is heated or otherwise treated, the substances behave differently, so that new protocols send different molecules to the detectors. The sample itself dates back to 2013; Freissinet's team had previously detected smaller organic molecules in the rock. However, the alkanes now found are significantly larger. The team speculates that they could possibly be the remains of fatty acids that have decomposed during sample treatment. However, organic molecules in the Martian soil can come from many different sources.
While living organisms produce such substances, they are also created by some non-biological processes. One possibility, for example, is that the alkanes were formed from hydrogen and carbon monoxide in circulating fluids deep in the Martian crust. UV radiation in the atmosphere can also enable complex chemistry and even in space organic molecules and their precursors are formed. Therefore, the molecules may have simply trickled down to the Martian soil with cosmic dust. Another alternative is that such substances are the traces of complex chemistry in lakes in the early days of Mars - perhaps similar to the processes that led to the emergence of life on Earth. Therefore, such chemical analyses are not just about Martian microbes, but can also reveal details about the interior of the planet or the former lakes on its surface.
