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Take for example, Neptune, a planet with a slushy mantle and outer core. Imagine we want to mine for water (or some substance beneath it - maybe an exotic ice form under all that liquid).

How do you go about mining into a liquid mantle/core? What would such a mining operation look like?

Some considerations:

  1. Keeping the hole open and controlled (high pressure geysers could wreck pretty much anything)
  2. Digging to a particular resource/point

Imagine that temperature of the substance we're mining isn't a problem - I assume the same basic principles apply whether you're mining into the Earth's mantle or Europa's underground oceans; only the materials used will change.

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    $\begingroup$ Europa's mantle and core aren't liquid; that's just the oceans below the ice on top. Planetary mantles and outer cores are almost always liquid, though. $\endgroup$ – HDE 226868 Feb 21 '15 at 19:30
  • $\begingroup$ Interesting. I thought of Europa's structure as having a thin "crust" ice and a "mantel" of ocean. But apparently there's a sea floor under there and a rocky mantle. $\endgroup$ – Josiah Feb 21 '15 at 19:34
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    $\begingroup$ Giving a comment answer for now since I can't dig as deep as I like at the moment: Why would digging vertical shafts be needed? A quick search on oceanic mining operations shows that they generally work just by dredging resources off the sea floor, rather than trying to tunnel like terrestrial mining operations. Sending down drone dredges that can break up the mantle, scoop up a bunch of the goodies, and come back for processing seems way more practical than trying to keep holes open in a wet, shifting substrate. $\endgroup$ – plagueheart Feb 22 '15 at 3:27
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    $\begingroup$ Here's a little more on deep sea mining from Wikipedia. It would use a bucket system or hydraulic suction and use robotic vehicles for initial exploration--seems like it might be the way to go. Someone with more planetary knowledge than me might be able to give an answer on how rapid the turnover of the liquid slush in an ice-core planet might be, which would be a factor in how profitable dredge or bucket-mining could be, as you wait for the volatiles of interest to diffuse into reach. $\endgroup$ – plagueheart Feb 22 '15 at 3:51
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    $\begingroup$ To expand on the deep sea mining reference. If we are ignoring temperature, then we don't need to 'mine' through the liquid...we just need to 'swim' down to the bottom of it and start digging, or use modern day deep sea drilling techniques (a la an oil rig). Depending on what material you are extracting. $\endgroup$ – guildsbounty Feb 23 '15 at 17:11
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It wouldn't be much different, at least conceptually, than what we do when we build Artesian wells.

Artesian well

We reach a spot underground at depth $d_0$ where the liquid is stored, and then place some device to capture the liquid and, if needed, pump it out.

Mind that the liquid pressure will make the level of the liquid rise into the access point we have drilled. If the pressure is high enough to make it sprinkle outside, we just need a valve in place to control the flow, else we will need to pump it from a depth $d_1$, with $d_1 < d_0$.

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my answers are for Neptune specifically, rather than for any liquid cored planet, though many principles used are generalise-able.

on a "small scale": you would need to use robots to physically go down and collect the liquid in the core from the gaseous atmosphere. there are two approaches to this. firstly you can make a robot-plane able to go all the way from the 'surface' to the deep high pressure centre, alternatively a sort of relay system could be made so many robots pass the liquid between each other each staying within their own band of pressure and altitude with an internal pressure to match. the relay goes all the way from the bottom to the top though no one robot does. both are viable and doable, though I strongly recommend the second.

on large scales: use a "centrifugal straw". the internal pressures in Neptune are a massive problem, however the temperatures are apparently not (being significantly under 5100k which while extremely hot is kind of workable with something like graphite since the high pressures raise the boiling point). back to pressure their is fortunately a way for a pipe to overcome arbitrarily high pressures. spinning the pipe (or rather an internal "support" in the walls of the pipe) will counter the inward force of the atmospheric pressure. since you can spin something arbitrarily quickly there is no theoretical limit to the pressure such a system can be built to withstand. the pipe could not be a suction pipe (https://www.youtube.com/watch?v=HUmZrtiXDik) and would need to support its own weight using buoyancy. power would be provided from large solar arrays in orbit or at the surface.

enter image description here sadly the only information i could get on neptunes core temperature is this very uncited image that looks like its from 2003 but that being said I will still be using it

on a very large scale: like eggs in a microwave! the core is big meaning it has a large volume to surface area ratio so if parts of it are heated they will keep that heat for a vary long time. so using an oscillating magnetic field, radiation or some kind of high pressure tolerance nuclear bombs dropped deep into the core you could heat the core up substantially. hot matter rises (admittedly you need to make it very hot if its going to rise through hydrogen and helium but its still doable especially given how cold neptunes atmosphere is) so large thermals of the core substances will start blooming in the atmosphere for 'easy mining'. odd but doable for any K1.(a bit) civilisation.

on an absurdly large scale: just mine the whole planet layer by layer with a vast legion of robots until you reach the juicy core. I mean why not? you were probably going to be mining the outer layers anyway, right?

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I'm no genius on certain substances and materials used for mining but these are the solutions I came up with.

Your question made me think of an ant hill, not sure why, but that's the image I got. I'm thinking a machine that, as it tunnels, it releases a sort of liquid that hardens immediately upon it's release, forming a tunnel behind it. Now this would probably only work for single passage tunnels because trying to mine through the already hardened walls would probably cause the liquid core to flood the entire tunnel.

Another thing, perhaps the liquid core is not like water but more like jello or something that bends and parts and doesn't squeeze back together. Or maybe something is added to the tunnel walls that makes them squishy and bendable, like adding jello mix to water.

Finding certain things and digging to a particular place would probably use something like a submarine radar where they send out sound waves and it bounces back when it hits something. Different sound waves maybe hit certain things and pass through other things, making it easier to find a certain thing.

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