I feel like this is a bit of a dumb question, but I've been reading some articles about the giant body of water scientists have found floating in space (e.g. Enormous water reservoir found in space is bigger than 140 trillion earth oceans) and was wondering how or if it was even possible to gather water floating in space?

I know that this specific body of water surrounds a quasar so it would be incredibly dangerous to try, but if there was another body of water found in an ideal location how might the water be gathered up?

EDIT I feel like I need to make a clarification, I am only asking about how water in the scenario talked about in the article might be gathered up. Perhaps my use of the word mined is causing some confusion but I am not asking about water that could be gathered from moons, asteroids, or any other rocky object found in space.


3 Answers 3


The short answer to the actual question asked: you might do it electrostatically, but it would require huge amounts of power.

The extended short answer: the water, though a nearly incredible mass of it, is spread over such a gigantic region that it is far less concentrated than in the air of the Atacama Desert, the driest place on Earth.

The doubly extended short answer: the water cloud observed isn't pure water. It will have lots of other not-so-potable stuff, like methane, ammonia, and hydrogen sulfide, mixed in with it.

OK, electrostatic "mining". I've used the Caltech Submillimeter Observatory (CSO) before and I know how they use it. The fact that the observers detected the water at millimeter and submillimeter wavelengths with the CSO tells me that the quasar is irradiating the water, exciting the molecules and causing transitions in their rotational-vibrational modes. Each such transition emits electromagnetic energy at a specific frequency. If you tune the CSO's receivers to 2 or 3 such frequencies specific to water and you see emission or absorption at all of them, then you have a pretty good identification that the stuff doing the emitting or absorbing is water. But quasars emit lots of radiation at energies much higher than mm or sub-mm, and just like UV photons from our sun ionize Earth's upper atmosphere, photons at those higher energies can ionize the water molecules (and everything else, too) in the cloud. They can knock a hydrogen nucleus (a bare proton) from a molecule, leaving H+ and OH-. The H+ often attaches to a neutral water molecule, making H3O+. The net result is that a lot of the water is ionized.

If you place electrodes in the cloud and charge them, H3O+ and H+ will be attracted to the negatively-charged electrode, while electrons and OH- are attracted to the positively-charged electrode. Bringing the H3O+ and OH- together (my guess would be that you do this by using magnetic fields to channel their motion) will yield two molecules of neutral water, which you can collect on a super-cooled surface. Bringing H+ and OH- together give one water molecule. When enough has been collected, you enclose that surface in a suitable container and heat it, driving the water into the container for harvesting.

Recombining those ions releases a fair amount of energy (in the form of photons and kinetic energy of the reaction products) which will tend to heat the apparatus, so some kind of cooling will be necessary. Essentially you're having to get rid of the energy the quasar dumped into the water molecules you're collecting.

OK, the concentration (atoms or kg per volume) of the water, with some back-of-the-envelope calculations. The article states that an amount of water 140 trillion times the mass of Earth's oceans is in the cloud. That's a lot of water! Specifically, since the mass of Earth's oceans is ~1.4 X 10^21 kg, that's ~2 X 10^35 kg of water, about 100,000 times the mass of our sun! But the article also states that it is spread over a region "hundreds of light-years across". If you assume it's 200 light-years across (the minimum to be "hundreds of light-years across"), and assume it's a toroidal region whose volume is about one quarter of the circumscribed sphere, then the volume of that region is about one million cubic light-years, which is 10^45 cubic km or 10^54 cubic meters! That's a lot of space! Spreading that much water over that much space yields an average concentration of ~2 X 10^-19 kg per cubic meter, which is less than one water molecule per cubic cm. This is a hard vacuum! At that concentration, and if you could extract every water molecule from the space you're "mining", to harvest a single kg of water you'd have to mine a region of about 5 X 10^9 cubic kilometers, which is a cube roughly 1700 km on a side. The apparatus to harvest reasonable quantities of water would be gargantuan!

Hmph. Doesn't sound worth it to me. Better to let natural processes concentrate nebular water into things like comets, asteroids, and planets, and then mine those objects.

OK, the water purity. After the big bang there was hydrogen, helium, a little lithium, loads of energy, lots of space (more and more as time progresses!) and precious little of anything else. It takes nucleosynthesis to make significant quantities of the "anything else". Nucleosynthesis occurs in such places as stellar cores, supernovae, and extremely high-energy environments like the accretion disks just outside of a black hole (farther-flung regions of the black hole's accreton disk are too low-energy to support nucleosynthesis). Regardless of the mechanism, in the long run these nucleosynthesis processes never yield one chemical species, like the oxygen to make water. They make all kinds of nuclei: oxygen, sure, but also carbon, nitrogen, iron, cobalt, sulfur, aluminum; various pathways in the various places make essentially all the naturally-occurring elements heavier than lithium.

The cloud contains oxygen to make water, along with the abundant hydrogen that permeates most of our universe. But there will also be nitrogen that with the hydrogen will make ammonia, and sulfur that will make hydrogen sulfide, and carbon that will make methane, and so on. If the observers at the CSO had tuned their receivers to ammonia or methane line frequencies they would have seen those molecules too. But probably weaker: in our sun there are about ten atoms of oxygen for each atom of nitrogen, and carbon is about 5 times more abundant than nitrogen. So while water might be more abundant than everything else...ever taste water with 10% ammonia in it? (Astrophysical measurements suggest lots of stars have carbon abundances higher than our sun's, some double or more!) You'd have to make sure you distill the water out of the miasma, and that takes power.

Net result: it's best to go to the naturally-concentrated sources like comets and asteroids, even if you have interstellar travel.

  • $\begingroup$ Wow, thank you so much for your answer! I always had a feeling collecting this water wouldn't be worth it but I was more curious about the how than anything else. $\endgroup$
    – yukimoda
    Commented Jun 27, 2018 at 1:21

That reservoir? Mere 12 billion light years away. So even traveling at speed of light - taking space expansion into account, you'd have some 30 billion years of round-trip. It's a curious discovery but completely unusable practically.

The most viable plans for mining water involve capturing comets. They have a large content of water ice, and are bound so loosely mining them with machinery wouldn't be all that hard. And if you need to deliver said water to a planet for terraformation, you don't even need to mine any significant amount - just enough to produce fuel to propel the comet on collision course with the destination planet. Of course all that water will evaporate on impact - but with enough comets the amount of moisture in the atmosphere will become sufficient to start rain.

  • 2
    $\begingroup$ Correction: It took light 12 billion years to make its way from that distant quasar to the Earth. Thanks to the expansion of the universe, that quasar was much, much closer to the nascent Milky Way when the light we see now was emitted 12 billion years ago, and it is much, much further than 12 billion light years away from us now. $\endgroup$ Commented Jun 26, 2018 at 15:06
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    $\begingroup$ I know that this particular discovery isn't practical it use. That's why I asked how water might be mined from a similar object in a more ideal location. $\endgroup$
    – yukimoda
    Commented Jun 26, 2018 at 16:55

There are water sources in our own solar system which are much easier to access. An example is Ceres, a dwarf planet in the asteroid belt between Mars and Jupiter. It could contain as much as 200 million cubic kilometers of water. In comparison, Earth as a whole, contains 1.4 billion cubic kilometers.

There are other objects with water in the belt that are much smaller in size, frozen and easier to mine. The question is really, what would you do with it once you mine it?

  • $\begingroup$ There's also water in NEAs in the form of hydrated clays. And ice in the lunar cold traps. A propellent source not at the bottom an 11.2 km/s gravity well would change the exponent in the rocket equation $\endgroup$
    – HopDavid
    Commented Jun 26, 2018 at 12:03
  • $\begingroup$ I am aware that there are moons and asteroids that contain water sources that would be more likely to be used. I was just curious how water might be extracted from a source made purely of water that no machine or device could physically land on. $\endgroup$
    – yukimoda
    Commented Jun 26, 2018 at 16:57
  • $\begingroup$ Ceres volume is 421 million cubic kilometers, if there is 200 million cubic kilometers of water, it would be over 47 %. Why should it be so much? $\endgroup$
    – Uwe
    Commented Jun 26, 2018 at 18:12
  • $\begingroup$ Based on this article: space.com/35052-water-everywhere-on-dwarf-planet-ceres.html scientists think the meteorites formed Ceres actually separated in the interior and were redistributed by processes like convection causing there to be so much water/ice under the surface. $\endgroup$
    – yukimoda
    Commented Jun 26, 2018 at 18:42
  • $\begingroup$ "The question is really, what would you do with it once you mine it?" Good question. I could "drink up," but there's no "up" in space. $\endgroup$ Commented Jun 26, 2018 at 22:38

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