Life on comets?

It has been widely known since the 1960s that some of the chemical ‘building blocks of life’ existed on some asteroids and comets, but it wasn’t thought that life could exist on them because of the extreme cold, radiation and vacuum in space. Now, in careful analysis of meteorite samples by NASA Goddard, the remaining DNA/RNA bases have been confirmed.

That still doesn’t mean there is life on them. A comet spends most of its time very far from the Sun, so any life would spend most of its life frozen, just occasionally thawing out.

Anyway, getting back to the point, just as finding the essential building blocks doesn’t mean there is life on them, being deeply frozen most of the time and exposed to radiation does it rule it out. A chemical reaction might slow to zero, and later speed up. After many accumulated years of being unfrozen, those reactions might eventually get to the point where life almost exists.

As an amusing diversion, I asked ChatGPT for its learned opinion:

“They do not have the kind of environment that can support complex organisms like penguins. Comets lack a stable surface for penguins to walk on, a source of food for them to eat, and an atmosphere for them to breathe. Additionally, the extreme cold, radiation, and vacuum of space would be lethal for penguins.”

Sorry, penguins are my favourite way of teasing ChatGPT.

A recent MIT study showed that reactions and their evolution can happen millions of times faster when taking place in small droplets, compared to large bodies of water. So compared to happening in an ocean, life-creating reactions taking place in the tiny drop formed as an ice crystal thaws on a comet would be rapid. As crystals melt and refreeze as the particles making up the comet shift relative to each other as it gradually melts and ‘outgases’, there would be a great many mixing and separation cycles. Merging and separation of water droplets is the sort of process I discussed in my non-cellular life book, the only key difference being that that was discussing droplets near hot springs, geysers and volcanic vents rather than on comets.

But the principle is exactly the same, and non-cellular life might therefore eventually evolve on a comet. It might freeze and thaw many times, but that isn’t necessarily a problem, and with the chemicals being regularly reproduced, radiation isn’t necessarily a problem either.

Making membranes and hence cells would be expected to take many orbits longer, and a comet might go extinct (its water burning off) before that happens. That means that if there is any life on comets, it is more likely to be non-cellular.

And… if there was life on comets a very long time ago, and a large enough one crashed into Earth with many fragments being separated and dispersing during entry, some of those life forms might have survived entry, and could therefore be the origin of life on Earth.

So, the usual theory, that building blocks either arrived from space or evolved here, and Earthly reactions in mud pools (or my small droplets) or wherever led to emergence of life might need to take greater account of the possibility that life actually came on comets. It already did allow for that possibility, it just dismissed it as highly unlikely, but I think recognising the much higher likelihood of non-cellular life compared to fully developed cells evolving changes the probability markedly.

Still just a theory, but in my view, a more likely one than it was.


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