To explore the sea under the ice in Europa, a probe with a nucleo-thermal tip has been suggested. Now as this probe melts its way downward, imagine we are pumping out the melted water. This should again be somewhat doable. When it finally hits liquid water below the ice layer, the water would be at such high pressure because of the weight of the ice layers everywhere else. Would this cause some kind of a cataclysmic pressure cooker explosion? What is wrong with this scenario?
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$\begingroup$ I think this is a great question, not sure why someone down voted it. It took me a while to realize that the sub-surface oceans are not under a huge amount of pressure. It was only when I remembered ice fishing when I was young that I made the connection. $\endgroup$– uhohFeb 10, 2018 at 17:29
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2$\begingroup$ ...This seems much more fitting to Worldbuilding. Hypotheticals and mass destruction are kind of specialties there... $\endgroup$– jpmc26Feb 10, 2018 at 23:14
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$\begingroup$ I'd have to agree - I don't see this question as on topic. It's just basic science. $\endgroup$– Rory Alsop ♦Feb 11, 2018 at 9:08
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$\begingroup$ I don't think this is on-topic for Worldbuilding; it's not about building a world. We don't take random hypotheticals there. $\endgroup$– HDE 226868Feb 11, 2018 at 14:59
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$\begingroup$ @HDE226868 It could be trivially formulated into a question about w̶o̶r̶l̶d̶ solar system building. I believe it would fit under the science-based tag or possibly the reality-check tag, asking if this proposed method of blowing up Europa for some purpose would work. $\endgroup$– jpmc26Feb 15, 2018 at 7:44
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2 Answers
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No. The water and ice are almost certainly under hydrostatic equilibrium. The ice is floating on the water. If you cut a hole in the ice, the water would fill the hole only part way, just like ice fishing. See this answer from someone who knows about these things.
While there are observations of water geysers from some moons in the solar system, the water is not coming directly from the sub-surface ocean. These are believed to be caused by trapped pockets of water within the ice, and rocket scientists will find the throat and expansion "nozzle" surprisingly familliar!
The reason they appear to "shoot straight out" is not because its a liquid spraying. It's a molecular phenomenon, and the water doesn't condense into liquid until after it's already out in space hundreds meters or kilometers.
So there's no reason to think that the oceans are under pressure, or there would be an explosion or great release of pressure. Any large excess or non-equilibrium pressure would relieve itself quickly since the ice is constantly cracking and opening, as demonstrated by the active lines of freshly frozen water on the surfaces.
See this very long answer where I show the same photos also!
You can read more about the differences between Europa and Enceladus in the question Enceladus; why use the words “geysers”, “jets”, and “plumes” interchangeably? Briefly, since the masses are so different, the dynamics of the plume evolution is very different.
above: Image of ice fishing from here
above: Figure 3 from Jared James Berg's thesis Simulating water vapor plumes on Europa.
above: Figure 3a from Porco, DiNino and Nimmo (2014).
above: "Europa's ice-trapped lake sits above the ocean in an illustration, Illustration coutresy Britney Schmidt and Dead Pixel FX, University of Texas at Austin" from National Geographic's "Great Lakes" Discovered on Jupiter Moon? (cropped).
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1$\begingroup$ I just saw this question and answer for the first time. It turns out at least some of the geysers at Enceladus do indeed come directly from the subsurface ocean! That's the only way they can explain the salt content and its confinement to the larger grains. Above that ocean surface, in a vent and above it, there's no liquid water. The pressures are so low the water sublimates: gas goes directly to solid, as the pressure and temperature drops going through the "nozzle". That the formal use of "sublimation" is for both directions (solid->gas and gas->solid) always bugged me. $\endgroup$ May 15, 2018 at 6:32
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$\begingroup$ @TomSpilker can you explain further what "geysers... indeed com(ing) directly from the subsurface ocean! means? I understand that the salt content of a given plume would tend to disqualify the source being melted ice in a pocket, but does sublimation really bring salt with the gas? Has it yet been explained how the salt might be transported from solution to space? If you are interested in answering this as a separate question where you can write an answer (as opposed to a new answer here) let me know and I'll ask something like "how does salt go from solution to space" but with fancier words $\endgroup$– uhohMay 15, 2018 at 6:42
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1$\begingroup$ Yes, go ahead and ask the question and I'll answer. $\endgroup$ May 15, 2018 at 16:53
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$\begingroup$ @TomSpilker How is salt transported from the subsurface ocean and ejected with the plumes of water from Enceladus? $\endgroup$– uhohMay 16, 2018 at 12:58
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$\begingroup$ I see you deleted your question about this. A proper answer will take more characters than a comment allows, so I'll ask and answer my own question. $\endgroup$ May 16, 2018 at 16:45
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It won't be cataclysmic. Europa's ocean already vents to space, a probe would just add a small channel to that.
A narrow channel several km long will also clog up quickly because the liquid water will freeze to the walls of the channel.
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$\begingroup$ Double check the other answer here (and in the linked material in Astronomy SE), especially about the mechanisms that are believed to produce these. $\endgroup$– uhohFeb 10, 2018 at 17:37
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$\begingroup$ ...the sub-surface vent looks (superficially at least) like a rocket engine! $\endgroup$– uhohFeb 10, 2018 at 18:07