Originally published at: Europa Clipper heads to Jupiter to search for alien life - Boing Boing
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But definitely not landing there, right? 
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I’ve never understood where life in a subsurface ocean is supposed to gets its energy from in absence of both light and oxygen. I guess the hope is to find if there’s some other chemical reagents available in unreacted form for some reason, but I’m not sure why there would be.
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in the Jupiter neighborhood, tidal flexing maybe
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Like what Earth has around hydrothermal vents? (One hypothesized location for where life actually got started here.)
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But then look at the description of chemosynthesis there – using the oxidation of inorganic compounds. Where do they get an oxidizing agent? Usually it’s oxygen, or else ions like nitrate or sulfate formed from it. Our oceans have these in constant supply because of photosynthesis at the surface, and otherwise they’d have been used up billions of years ago. It doesn’t address the question for Europa.
The amount of energy you can capture from a thermal gradient is relatively small, and something would have to be huge to actually experience a noticeable gradient from tidal heating. In theory it could power some kind of geological activity, like hydrothermal vents…but then see above.
I don’t know, I’d feel a lot more optimistic if someone ever explained how this could possibly work, instead of giving analogies to Earth ecosystems that aren’t nearly as isolated as people portray.
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maybe something like this? ‘Dark Oxygen’ Discovered Coming from Mineral Deposits on Deep Seafloor | Scientific American
ninja edit since that is paywalled - Dark oxygen - Wikipedia
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I hope they do a “blind” survey of earth, seeing what conclusions they would draw solely from the data they collect - and only then compare it to the reality we know.
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If the likely water oceans exist on europa, oxygen is no problem since life would get oxygen the way that creatures at the bottom of the sea harvest oxygen from the water around them. Light isn’t required as creatures in caves, bacteria deep in the earth’s crust, and creatures at the bottom of the sea show. Energy could easily be harvested from chemical reactions with the thermal input of tidal flexing melting deep layers of the crust.
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Chemoautotrophic metabolism, as is hypothesized on Earth, i would suppose. Photosynthesis was a (relative) latecomer to the party. There should be an energy gradient to tap just based on the tidal heating. But it would depend on the minetal makeup of the ocean floor. And, of course, is a total guess based on our n=1 experience on our own planet.
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I’d venture to say improbable rather than impossible
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i am no astrobiologist, but i have always assumed that the intense radiation from the planet would somehow provide the “Frankenstein Spark” to mineral- and oxygen- rich environs of the subsurface ocean on Europa.
but i read too much pulp sci-fi in my youth.
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What chemical reactions? Life as we know it all gets its energy from breaking down food, which would need a source, or by combining reducing agents with oxidizing agents. Those might exist together for some time, as suposed when life first formed, but in the long run they’d annihilate each other. On earth we get new reducing agents bubbling up from below, which then meet a separate environment with oxidizing agents that are constantly replenished by photosynthesis. Potentially you can also get an oxidizing atmosphere from photochemistry but that still takes light. What might be happening here instead to keep the whole ocean from getting reduced over geological time?
(And incidentally, photosynthesis is probably not all that late. Oxygen production maybe, but there are other types…some archaea even harvest light energy from retinal instead of chlorophylls, which might go back a long time.)
It really bothers me that even scientists will casually talk about the possibility of life here without ever considering that question. Like, is it not interesting? It wouldn’t be helpful to have even hypothetical answers as to how a Europan ecosystem might be powered, beyond handwaving about tidal heating? Because right now it feels like listening to one of those libertarian island projects, where everyone is excited about the possibilities and nobody cares about the basics. Am I crazy here?
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No, and I’m liking the detail-oriented thinking.
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Not my field, obviously, but i found this:
As far as whether it would be exhausted over time, i guess it depends on the details, of which we are totally ignorant currently. Additionally, how it started would be only a starting point for evolution to work from. If life got started, it would probably find a way.
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See, here is where I disagree. I think if you lock living things in a cold dark box with no energy input, they will survive until the food (like prebiotic broth) is all used up, and then they will die off. Evolution isn’t magic. Even on earth, we still have places where things have to at least go dormant until some trickle of light, nutrients, or oxygen shows up again. If there are any ways forward on Europa – well, that’s the question, right? But I think it would be valuable to know if there are at least some theoretically possible answers.
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Like i said, not my field. But i have an inherent block against “impossible.” I tend to think it needs to proven impossible rather than assumed so. There are way too many unknowns about what is actually going on to say we know anything at all. And again, bading any conclusions on a single case study is pretty fraught.
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Thermodynamics places some hard limits on what can exist. But believe it or not, I’m not arguing life on Europa is impossible. I’m saying figuring out how it could be possible should be the first step in considering that, and that it seems to be going completely unaddressed, and it’s frustrating.
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