Is science sometimes in danger of getting tunnel vision? Recently published ebook author, Ian Miller, looks at other possible theories arising from data that we think we understand. Can looking problems in a different light give scientists a different perspective?

Life On Other Worlds?

The February edition of Chemistry World had an article on the prospects for life throughout our solar system, and this was of interest because I intend to give a paper at an International Conference on Astrobiology in Rotorua in June. In my opinion, many of the statements in this article were overly optimistic, which raises the question, when would chemical signatures indicate the possibility, even, of life. The problem is, a chemical signal only indicates one thing when the set of possible causes leading to the signal has one element.
The article stated that there were three essential needs for life: an abundance of chemical building blocks (although these were unspecified), liquid water, and an energy source. The article seems to think that heat is adequate for an energy source, but I disagree. I think photons are critical. The reason comes from the thought that one key requirement for life is that it can reproduce. To do that, it needs a functional group that can link the information-carrying mers into a polymer, and that requires two bonds. Such links also need to be able to be hydrolysed, but not too readily. The reason for this is that initially we are going to get random polymerization, and if the consequences are effectively locked away for ever, we run out of raw materials before something sensible appears. Finally the link needs a variable solubilizing ability because to reproduce, there has to be a way to pull the strands apart so they can act as scaffold for new duplexes. (Without a duplex you have no means of transferring information to the new entity.) The only trifunctional linking group that I see as satisfactory is phosphate, which links through ester formation. Further, it is only marginally satisfactory, because divalent cations usually precipitate phosphate. Our modern life forms might be able to use very dilute phosphate solutions, but the initial life forms would not.
The only way I know of that has been shown to lead to adenosine monophosphate (as well as ATP) was powered by light. Accordingly, anything under permanent ice will not get such light. The issue here is not whether life could live there; it is whether it could evolve there. That alone, in my opinion, rules out the ice moons. Equally, if they do have liquid seas, we would expect some weathering of the dust, and the extraction of calcium and magnesium into the waters. That would remove most phosphate from the waters.
A further issue with reproduction is the necessity of having prodigious amounts of reduced nitrogen material. The Saturnian moons avoid this difficulty, as they seem to have or seem likely to have, ammonia in their oceans, if they have oceans. Enceladus has had ammonia detected in its geyser effluent. Europa has an extremely tenuous atmosphere. The most common species are oxygen and hydrogen, which are products from the photolysis of water. Also present are oxygen atoms, hydroxyl radicals, sodium, and at up to five orders of magnitude less common than oxygen, carbon dioxide and sulphur dioxide.  These species are believed to be formed by photolysis of surface ice, or ice fragments ejected by sputtering due to high-energy particle impacts. Despite measurements over five orders of magnitude in concentration in barely detectable pressures, there are no nitrogen species detected. This, at least, is in accord with what is outlined in my ebook "Planetary Formation and Biogenesis": Saturnian moons potentially have nitrogen because they were formed by the coalescence of dust/ice, where the ice had methanol and ammonia within it. By the time the dust got to the Jovian system, the ammonia and methanol had boiled away in the higher disk temperatures.
Accordingly, in my opinion, there will be no life in the outer solar system. So what about Mars? That is a more complicated story.
Posted by Ian Miller on Mar 4, 2018 8:44 PM Europe/London

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