Astronomy

As usual, I'm going to link to the journal article in Astrobiology. The conclusion reads:

We agree with Carl Sagan’s claim that extraordinary claims require extraordinary evidence (Sagan, 1979) and understand that any purported detection of life on Mars will necessarily be met with intense scrutiny. In addition, in practice with established norms in the field of astrobiology, we note that the certainty of a life detection beyond Earth will require multiple lines of evidence. Nevertheless, our approach has led us to estimate that the Cumberland mudstone conservatively contained 120–7700 ppm of long-chain alkanes and/or fatty acids before exposure to ionizing radiation. We argue that such high concentrations of long-chain alkanes are inconsistent with a few known abiotic sources of organic molecules on ancient Mars, namely delivery of organics by IDPs and meteorites, atmospheric fallout and deposition from photochemical haze, and organic production from serpentinization and Fischer–Tropsch reactions on the Red Planet. In contrast, it is not unreasonable to hypothesize that an ancient martian biosphere would be capable of producing this level of complex organic enrichment in martian mudstone deposits, and that allochthonous delivery of hydrothermally synthesized organics could have contributed to the abundance of alkanes found in the Cumberland mudstone. To improve the ability to predict the types and concentrations of organic molecules that could have been preserved in ancient sedimentary rocks exposed to ionizing radiation at the martian surface––regardless of their origin (biotic or abiotic)––we recommend experimental studies that determine the radiolytic degradation rates of kerogens, alkanes, and fatty acids in Cumberland-like Mars analogs under Mars-like conditions.

I didn't realise curiosity was still creaking around out there doing science. I also didnt realise it could conduct experiments on old samples. A sensible but extraordinary capability.

Skeptics guide podcast was saying once that even if positive evidence of life on Mars was discovered by a rover, it would need to be confirmed / reproduced by a lab on Earth before being credible science.

IIRC there's a mission plan for an uncrewed mission to return samples from the rovers but its not funded or scheduled.

I am skeptical of the premise that long chain hydrocarbons can only be explained by life. Mostly because that logic fails whe examining how life arose on Earth in the first place. If complex organic molecules can only form life, then how did life arise on Earth to begin with? Life itself is complex organic chemistry and large organic molecules. If complex molecules like polypeptides and RNA can't form without life, then life can't come into being in the first place. Particularly with these long chain hydrocarbons it's not that hard to imagine exotic conditions where they might be able to form. It is certainly easier to imagine these conditions than imagining the self replicating RNA or polypeptide strands that most likely became life as we know it. If they had found chains of nucleic acids or amino acids I would be a lot more willing to buy that it's a sign of life. But hydrocarbons? It's definitely interesting and a very good thing to look into (particularly in terms of the origins of life) but it's far from a smoking gun.

That said, I am very interested in this finding because, at the end of the day, I do think it is relevant to biochemistry. Mostly that there are two possible explanations and both are important. If it's not proof of life on Mars (I don't think it is), then it is proof that complex organic molecules have formed elsewhere in relatively normal chemical conditions in the universe without existing organisms, which is a major unsolved problem in trying to determine the origin of life.