A very simple illustration of my idea

Would it be possible that on an ice moon like Europa, except more massive, that large volcanoes/thermal vents would be able to reach the surface and create hot springs for life to survive around on the surface?

And if it is possible, what should the depth of the subsurface ocean be in order to allow this?


2 Answers 2


Yes, this seems quite plausible, based on what we know from observations of Saturn's moon Enceladus.

Enceladus is quite icy, like Europa. Unlike Europa, it is known for its magnificent assortment of geysers from cryovolcanoes, spewing volatiles into space. It makes sense to ask whether there might be hydrothermal activity akin to the deep-sea vents on Earth that allow life to thrive on the bottom of the ocean. Analysis of the plumes of the geysers indicates that, yes, there are hydrothermal processes taking place that could provide an energy source for life (Hunter et al. 2017). It's even been argued that some of the methane found in the plumes could be due to biotic processes (Affholder et al. 2021).

The question, then, is whether the hydrothermal activity on Enceladus' sea floor means that a moon could have surface hot springs -- and I honestly don't see why not. A relatively shallow ocean might make it easy for cryovolcanic features to poke their way up toward the surface -- or for heat and necessary organic molecules to propagate upwards from deeper active regions.

It's also worth noting that Enceladus is only about 1/6 the radius of Europa, and that a more massive parent planet than Saturn, combined with a somewhat different orbit, could increase the amount of tidal heating available, providing opportunities for more dramatic cryovolcanism.

  • $\begingroup$ Okay! So would there be a limit for the depth of the ocean? Since I don’t really know how tall thermal vents could actually be in that situation $\endgroup$ Apr 17 at 14:52
  • $\begingroup$ @MrUnavailable I don't know -- hopefully someone else can provide an estimate. $\endgroup$
    – HDE 226868
    Apr 17 at 15:05

I started this as a comment, but it is too long.

It is theoretically possible for life to exist within an icy moon of a giant planet, if conditons are right, in hypothetical liquid water oceans beneath many kilometers of ice. Of course nobody knows yet if there is such life beneath any ice covered moons.

The ocean water will not evaporate due to low (or no) atmospheric pressure and then be split into hydrogen and oxygen by ultraviolet light and the gases escape from the moon, turning the moon dry. Because the many kilometers of ocean will separate the water from the vacuum of space and from the ultaviolet light.

If it is possible for life to form and exist in a global ocean beneath many kilometers of ice, it may be possible for that life to presist for countless billions of years, and maybe develop multicellar life and maybe develope intelligence and a strange underwater civilization.

Of course it would very difficult for explorers from Earth to detect such life beneath many ckilometers of ice, let alone make contact with any hypothetical civilization in the subsurface ocean.

In the case of surface hot springs on the surface of an ice-covered moon, fed by a vast subsurface ocean, the surface springs would be the surface and thus exposed to the vacuum of space. So the water would boil away into water vapor and either freeze out as snow or be split into hydrgen and oxygen.

And then that gas would escape into space and the surface of the hot springs would be bubbling and boiling as water rused upwards to replace the water lost into space. Unless the moon had a dense enough atmosphere that the surface pressure would make the boiling temperature of water higher than the surface temperature, so the water would not evaporate very quickly.

To retain a sufficient atmosphere the moon would have to posses a high enough escape velocity, not surface gravity, to retain at least the heaviest common gases for geological eras of time. And it would be good if the escape velocity would be high enough to retain water vapor in the atmosphere and oxygen in the atmosphere for geological eras of time. If you want multicellur plants and animals in the surface pools, they will need to get oxygen from the air with lung equivalents or from the water with gill equivalents, and it will be unlikely to have enough oxygen in the water without a dense oxygen-rich atmosphere.

I think that most life forms adapted to the conditions of the subsurface ocean would die in the different conditions of the surface pools. but some lifeforms might surface and feed on the corpses of the life forms which don't surface. And from the few survivors, more complex lifeforms adapted to the surface pools might evolve, creating a new biosphere as rich as that of the subsurface ocean.

Or possibly no living lifeforms ever make it from the subsurface ocean and all life in the surface pools evolves separately.

In any case, the lifeforms will need much time and space to evolve into complex multicellular life forms with a diverse biosphere in the surface pools. So the surface pools should be very large, like very large lakes, or even like oceans. And they should be permanent.

If the surface pools last for only millions of years instead of billions of years there might not be time enough for life forms advanced enough for the needs of the story to evolve in them.

Also each surface pool, lake, or ocean might evolve totally different lifeforms.

Of course, if the surface waters sometimes erupt in vast geysers many miles high, and the winds blow the water for tens and hundreds of kilometers or miles before falling down on the ice, many seeds and larvae may be carried vast distance before landing on the ice and dying, or landing in othersurface water and surviving, thus preading the life from one pool to another.

On Earth, flying creatures often spread various lifeforms from one body of water to another.

A rain of animals is a rare meteorological phenomenon in which flightless animals fall from the sky. Such occurrences have been reported in many countries throughout history.1 One hypothesis is that tornadic waterspouts sometimes pick up creatures such as fish or frogs, and carry them for up to several miles.[1][2] However, this aspect of the phenomenon has never been witnessed by scientists.[3]


Surface pools might form over volcanic hot spots on the surface of the moon's solid core, which could heat up the water and ice above the hot spots.

You do not want the moon's surface to be hot enough melt all the surface ice, otherwise you would have a moon with a surface ocean instead of surface pools in the ice.

And if the moon has a very strong tidal heating much of its heat may have an internal source instead of coming fro sellar radiation. The surface pools of water and the "chimneys" of water below them might conduct the interal heat to a few spots in the surface where it spreads into the atmosphere and isn't strong enough to raise the surface air above the melting point of ice.

And the surface conditions on the moon might change over time, perhaps eventually dooming the life in the surface pools.

  • $\begingroup$ Thank you! So would there have to be a limit to the ocean depth given that I don’t know how tall volcanoes/vents can be? $\endgroup$ Apr 18 at 14:18

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