I truly don’t think that can be a real conversation based on our current (lack of) knowledge of the actual circumstances on-site. Anything can be speculated right now. I’m leaving that to folks with better understanding of the effects of that radiation level on compounds on the surface, the potential cycling of the surface down to the subsurface ocean, interactions between the ocean and whatever is on the bottom, as well as the geology going on further down. There is also potential interactions with other moons and crud loose in the system. Too many unknowns, and always more complex than it seems like it ought to be. Very much looking forward to filling in some of those blanks!
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The article we’re all commenting on is a bit misguided in saying that Europa Clipper is going to Europa to search for alien life. It’s going there to characterize Europa’s subsurface ocean. It really has no way of determining whether there is life in that subsurface ocean, unless any life that exists there does something so blatantly obvious that it shows up on radar or spectral analysis of Europa’s surface.
But on the point of oxygen being necessary for life, may I point out:
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Yeah, and where does that elemental sulfur come from? Why hasn’t it all hydrolyzed a long time ago? My understanding is that for the most part it’s from reduction of other forms like sulfate…and those are replenished by sulfur-oxidizing bacteria, which generally depend on light or oxygen, or just by reaction of sulfides with our oxiding atmosphere. There’s a sulfur cycle. It’s not a fuel that just comes out of nowhere.
Seriously, what part of what I’ve written makes people think lithotrophic bacteria are something I’ve never heard about? 
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I’d always assumed it came from https://www.sulphurinstitute.org/
/s
Wild speculations aside…
I think we can all agree that if/when the Clipper gets there and we all say “huh that’s weird” it would be the best possible result.
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Elemental sulfur and sulfates can come from other chemical processes than biologically-driven ones, just like molecular oxygen can come from other chemical processes than photosynthesis. Life had to initially evolve in an environment with very little molecular oxygen, and sulfur-reducing bacteria may descend from the earliest life that existed before the evolution of photosynthesis.
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I’ve been letting this percolate in my head overnight, and this popped out. Pure speculation and all, but even so.
Even in our pretty cushy blue-green oasis, some critters have developed pretty impressive radiation resistance. See Deinococcus radiodurans. I could postulate that under the intense radiation environment of Europa, (assuming life could get a toehold) something could outdo this critter pretty easily*, and perhaps even develop a pigment or some such that could harness that radiation (with perhaps some degree of shielding, for instance, only found at certain depths in the ice) and use it to split the water molecules to free either oxygen or hydrogen for further use as a reactant. Is this feasible? I have no idea. But it could be the basis for a sci-fi plot!
*Recently read an article suggesting that the radiation tolerance of Conan the Bacterium may be unrelated to radiation at all, but developed as a way to survive desiccation. If this is so, a critter that was under direct pressure to survive intense radiation could pretty easily (I would assume) find more effective ways to do so. Maybe?
“Damn it. Jim. I’m a doctor! Not a theoretical astrobiologist!” 
Oxidative Stress Resistance in Deinococcus radiodurans - PMC (nih.gov)
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Except that’s not really what Europa is. Energy is necessary for life as we know it — in fact it is life as we know it. Earth is blessed with an infinite supply of energy (at least for the next 4 billion years or so). Europa also has an infinite supply of energy through Jovian tidal forces. For light eaters, tidal-thermal energy is almost incomprehensibly exotic. But we have analogs on earth: bacteria and simple life-forms living around hydrothermal vents.
Are these world spanning complex ecosystems? No. Not here. But they exist, and hint at what could be possible on other worlds such as Europa. Is it enough to sustain life on Europa? Who knows, but it’ll be fun to find out, and we’ll learn a ton of new things even if it turns out to be a bust.
The core question seems to be “how did life begin.” Barring it being magicked into existence in situ, how did we get from a barren ball of cooling magma to the complex multicellular life forms that now cover nearly the entire surface of the planet? And could life have taken a different path? One that doesn’t rely on abundant light and heat from a nearby star? Or rely on oxygen? We really don’t know since light dependent aerobic life apparently outcompeted other possibilities here on earth, which is why we study exotic life forms and want to head to Europa for hints at what could be possible.
Given that hydrothermal vents were discovered in 1977, opening new possibilities about how life could evolve, I personally am excited to learn what the Europa Clipper uncovers, even if it is merely that Europa is a lifeless ball of dirty water.
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Yeah, if you look, I mentioned hydrothermal vents. My question was how you could have reagents to keep redox reactions going for literal billions of years without some mechanism to replenish them. Hydrothermal vents provide reducing agents, but then those would exhaust the oxidizing agents, which are ultimately replenished from our atmosphere. That means they’re not actually independent of light and so don’t provide a model for how to survive on just tidal heating.
So far I have had two responses make any attempt to consider the problem, and four assuming I must somehow not know about lithotrophic bacteria and vent ecosystems, like they’re some obscure thing instead of a regular occurrence in nature documentaries. Even after I’ve been talking about them. It makes this topic extremely frustrating, and I think I’d rather call it here than keep explaining the same issue again and again, thank you.
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The radiation environment of high-energy charged particles near Jupiter won’t penetrate the surface of Europa and wouldn’t reach a subsurface ocean deep under the ice, and hence any life in that ocean couldn’t use it as an energy source. At most radiation might drive some chemistry on the surface that could eventually filter down into the subsurface ocean.
Say what now? 
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I agree there are no perfect analogs in Earth life to any life that might exist in a subsurface ocean of an icy moon, because life on Earth has been evolving in the presence of copious atmospheric oxygen for something like 2 billion years now and there’s probably nothing left of pre-photosynthetic life. Sulfur-reducing bacteria are suggestive of how life might exist without any dependence on oxygen metabolism or photosynthesis, if geochemical processes could replenish the chemical energy sources such life would use.
No, i am referring to a biota in the ice. Now, i have no clue how far the radiation would penetrate nor how plausible this would be, but if there are vents allowing the ocean access to the surface, it would seem plausible that a bacteria or archea equivalent could colonize said vent at whatever depth would be necessary. Understand, entirely hypothetical, but could get around the issue of use up all the goodies, and then die.
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A name given D. radiodurans because it seemed that we could not kill it. And because it’s funny. Nerd humor, you know.
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Cool, it’s real
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Obligs:
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https://www.pnas.org/doi/10.1073/pnas.2316452121
Bioenergetics of iron snow fueling life on Europa, PNAS
relatively recent theory, so it may not be directly testable this time.
Here’s the instrumentaion loadout on Clipper.
Thank you, that makes sense. Life still being powered by radiation at the surface, but instead of being absorbed directly for photosynthesis, it creates a series of oxidized intermediates that can accumulate in the ocean below. I wonder how much might actually find its way – the ice is over a dozen km thick and doesn’t seem too dynamic over short time scales – but if some transport is considered plausible, it at least gives a possibility that could be investigated.
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There’s also a potential source of oxygen in the subsurface ocean environment of Europa if the right kinds of minerals exist.
It doesn’t sound like they’ve entirely figured out what’s going on, but in the presence of those nodules the amount of dissolved oxygen increases.
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Does it go completely unaddressed or does it go completely unaddressed in the media?
Because I have a hard time believing that actual xenobiologists don’t spend a lot of time thinking about exactly these questions. It’s just that a lot of nuance gets lost in communications with the public, at least in my experience in completely different fields.
