[ShredKazoo]

It's incredibly cold in the outer solar system right? So why is it that there is liquid water in these moons? Is it some sort of geothermal heating?

What's the most complex life which could conceivably exist in such a cold environment? Presumably there's very little sunlight penetrating through the ice to the liquid ocean.

[akiselev]

Tidal heating [1]

[1] https://en.m.wikipedia.org/wiki/Tidal_heating

[Aardwolf]

Interesting stuff! Made me find that even rogue planets (free floating without orbiting any star) might theoretically be warm enough to support oceans and life: https://en.wikipedia.org/wiki/Rogue_planet#Warmth

[PaulHoule]

Could be either tidal or geothermal. It’s been conjectured that even Pluto could have liquid water inside.

The point is that generic small outer solar system bodies have liquid water, whereas the generic inner solar system body doesn’t. If you think liquid water is the most important requirement for life then most of the habitat in the universe is outside the frost line.

It’s totally plausible that simple life could form around geothermal vents on such a moon but harder to believe you could support a complex ecosystem enough to evolve intelligent life without sunlight.

At the high pressures in such an underground ocean I wouldn’t expect our proteins to work, you can kill bacteria with very high pressure. I suspect that proteins that evolved in that environment could work just fine. I can picture a creature from that kind of world drilling up to the surface somehow, but the low pressure would be deadly and in a system like Jupiter where Io ‘breeds’ radiation (vapor from volcanos gets ionized, gets accelerated, ionizes more vapor) the surface could be a dangerous place.

Such a creature though might have a leg up on starfaring as getting into orbit might be easier (never mind building a beanstalk) and rather than being tempted by boring destinations like Mars (smaller planet, smaller civilization) they might go straight to cutting up wet/carbonaceous asteroids to build large (100-1000x more habitable area than Earth) habitats and if they developed D-D fusion they might be quicker to see the advantages of a comet-hopping lifestyle.

[lumost]

One of the Main limiters with underwater intelligent life would be industrialization. How are you going to use a steam engine underwater? What do you burn to heat it? Given that geothermal vents would be the source of life for such a species - capping them for machinery would also be unwise.

[awb]

Any motion can be used to do work. If there are underwater currents, that power can be captured and used.

[polishdude20]

Why would geothermal vents be a source of life after the species has evolved reproduction?

[pc86]

In the same way our sun is for us. Life on Earth wouldn't last very long if you plopped a Dyson sphere between it and the sun.

[PaulHoule]

Source of energy and materials…

[sanxiyn]

From Earth's hydrothermal vents, we know sunlight isn't necessary for life although energy is.

[Mistletoe]

We don’t know if life started in the light though and then migrated to the vents and adapted. My memory of it is that this is an unanswered question so far.

[dcminter]

It's definitely an open question. But in his book "The Vital Question", Nick Lane makes an interesting case that they're actually the origin of all life: https://nick-lane.net/books/the-vital-question-why-is-life-t...

[causality0]

We know that life is older than photosynthesis. I'm not aware of another light-dependent metabolic process that could predate chemosynthesis.

[peter303]

Its a good hypothesis that life start at deep volcanic vents. Geologist Robert Hazen conducted lab experiments showing that all steps of the metabolic citric cycle occur in this environment without needing catalytic enzymes. Chemical reduction of magma provides the energy. As life developed enzymes to improve metabolism, it could migrate to colder, lower pressure environments.

[wkat4242]

It's also awash with radiation from Jupiter. If there's life, it won't be as we know it :)

[jvanderbot]

Europa is enticing because life would exist under a few km of ice, more than enough to prevent radiation from causing too much problems.

The hydrothermal vents, where the main sources of energy are hypothesized to be, would be deep enough.

[zirgs]

Water is really good at radiation shielding.

[jvanderbot]

I've heard that if you swim into a nuclear reactor spent fuel containment pool, you will actually measure the least radiation somewhere in the middle of the pool, thanks to shielding from the universe.

[dan_hawkins]

Spent Fuel Pool

https://what-if.xkcd.com/29/

[revicon]

The last lines are the best...

  But just to be sure, I got in touch with a friend of mine who works at a research reactor, and asked him what he thought would happen to you if you tried to swim in their radiation containment pool.

  “In our reactor?” He thought about it for a moment. “You’d die pretty quickly, before reaching the water, from gunshot wounds.”

[wkat4242]

I know someone who worked at a medical isotope reactor and there were no guns there, at least not in the reactor area. Security tends to be much much further outside ;)

After all, remember some things in a reactor don't react well to bulletsch.

[jvanderbot]

Nice, thank you!

[LatteLazy]

Does Jupiter emit any noticeable radiation?

[jvanderbot]

Jupiter's radiation is so intense that Europa Clipper has a _super weird_ mission profile (a bunch of fly-bys instead of an orbit) so that the spacecraft doesn't spend too much time cooking in all that.

https://europa.nasa.gov/

[peter303]

The current Juno probe flies in 53 day orbits where only a few hours are in heavy radiation. It has made 48 orbits. The mission has been extended 7 years to 2025. If Juno runs low on fuel or the hardware breaks down, it will be crashed into Jupiter to avoid hitting and contaminating a moon.

[wkat4242]

Yes.

https://solarsystem.nasa.gov/planets/jupiter/in-depth/

> Near the planet, the magnetic field traps swarms of charged particles and accelerates them to very high energies, creating intense radiation that bombards the innermost moons and can damage spacecraft.

So basically like our van Allen belts but supercharged.

[rob74]

Technically, the answer to GP's question would be no, because Jupiter doesn't emit the radiation, it just traps and accelerates the particles (mostly coming from solar wind) in its magnetic field...

[PaulHoule]

A lot of the radiation is produced by a ‘breeding’ process where volcanos on Io emit vapor that gets ionized and then accelerated to make more radiation that ionizes more vapor.

[pengaru]

Katherine de Kleer said "It's like Io is the massive polluter of the Jupiter system" on the Lex Fridman podcast #184, the Io part starts ~14mins in for the curious

[LatteLazy]

Thanks!

[southernplaces7]

The quick answer: Yes and from a human visitor perspective, lethally high amounts. It's the single most intense emitter of radiation in the solar system except for the sun itself. If we wanted to colonize any planet with plentiful moons, Saturn would be a much better candidate at least in this regard.

Also, though another reply here mentioned Jupiter not emitting its own radiation, this isn't quite correct. It does, almost like a small pulsar.