We state that these large amounts of long-chain alkane are not consistent with only a small number of known abiotic sources of organic molecules on ancient Mars.
That single sentence encapsulates an increasing conflict in the exploration of Mars: the instruments designed to analyze the ancient chemistry of rocks continue to give signals that would not be accommodated to a simple, non-living theory. It is the loss of the statement of biology, the shrinking of possibilities, radiation, mineral reaction, the planet Mars once was.
The Curiosity rover of NASA sunk into an old mudstone in Gale Crater fine grained sediment that was deposited in standing water. The onboard chemistry laboratory on Curiosity detected in that sample the largest organic molecules to be discovered on Mars: decane, undecane and dodecane. These hydrocarbons may be compatible with pieces of fatty acids, a well-known component of cell membranes on Earth, as well as are still compatible with some pathways in geologic history. The problem is that Curiosity is capable of recognizing molecules and the signature of them, but it cannot physically mark whether it is biological or not.
To test the possibility of the simplest non-biological explanation bearing the burden, researchers tested whether meteorite delivery and other known abiotic processes (could) explain what Curiosity measured. The group of research investigating the question of abundance in the drilled sample in the framework of an Astrobiology analysis declared that non-biological processes could not possibly explain the abundance. Another challenge that the work has dealt with was a physical eraser that has been scrubbing Mars over the eons: surface is subjected to cosmic ray because the planet lacks the global magnetic field and dense atmosphere of the earth. The researchers were able to estimate the amount of radiation the rock was exposed to over about 80 million years at the surface or near the surface, and then to model the degradation of the rock to construct the amount of organic material that could have been present before that long process of dismantling. The recreated initial concentration suggested concentrations that are larger than natural abiotic production circumstances are supposed to support.
The chemistry puzzle is next to another old Curiosity puzzle: the one with the appearance and disappearance of methane. Background methane which increases and decreases by the season, with temporary spikes which act like temporary plumes, such as a peak of about 21 parts per billion by volume, has been measured by the Curiosity mission using the tunable laser spectrometer. Curiosity, as NASA put it, lacks instruments that can provide a conclusive answer as to whether the source is either biological or geological or even whether the gas is old or new. Methane is a molecule with dual citizenship, just as the long-chain organics, as it can be produced by both life and rocks and water, as well as by Mars, concealing the route in the incomplete data.
The impact of these findings is the environment that Mars was probably offering at the time the rocks were being formed. Climate work based on data has reinforced the argument that early Mars existed in long periods of wetness and not just transient melting. Perseverance has investigated clay-bearing materials in Jezero Crater, the chemistry of which is consistent with changing over a period of time and under relatively low temperatures and persistent rain, indicating a potentially habitable early planet with a stable surface. A rock core at Jezero has also been described by the same mission as potentially bearing biosignatures a very cautious term which identifies interesting patterns without turning them into evidence.
In two rovers and two entirely different landing sites, Mars is now offering a unified engineering challenge in astrobiology: preservation of delicate molecular remains in hostile radiation, interpretation with instruments required to be autonomous, and separation of products of life and ingenuity of chemistry. The evidence of organisms in the mudstone of Gale, as yet, is a stepping-post a post which strains the explanations of non-life, without bringing the case to a close.
