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So, in light of my previous question: how long would it take to bring water to Mars?, assuming that humans have established a magnetic field and atmosphere thus far, what it the fastest way to then give Mars a sizeable ocean of about 50% water cover? By “fastest”, I mean in a timespan of 100 years or less.

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    $\begingroup$ Do you realize you are asking "what is the fastest way to run the 100 m in 10 seconds?"? $\endgroup$
    – L.Dutch
    Dec 20, 2022 at 14:36
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    $\begingroup$ @L.Dutch More like "what's the fastest way to run the 100m in under 3 seconds?" $\endgroup$
    – Zeiss Ikon
    Dec 20, 2022 at 14:41
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    $\begingroup$ Also, please note that the task you are trying to make humanity do is herculean, to say the least. You might want to lower your expectation of filling Teraliters (or anything close to this number) of water in such short time with a scientifically plausible solution, if even such thing is possible ^^'. Might consider to incorporate some science magic to make it work within your conditions. $\endgroup$ Dec 20, 2022 at 15:04
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    $\begingroup$ Easy: magic. Just click your fingers, and there's an ocean. Or were there some important constraints that your question is currently lacking? $\endgroup$ Dec 20, 2022 at 15:10
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    $\begingroup$ Teleportation should do the trick. Assuming you have the mojo to open multiple large portals, and you don't really care about messing up anything on the moons of Saturn, can probably get it done this weekend. We'll need to get started early though, I have plans for the afternoon. $\endgroup$
    – John O
    Dec 20, 2022 at 15:18

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A frame challenge: bringing oceans to Mars in 100 years is impossible unless you also build crazy huge space radiators to dump the excess heat or invent magic that casually violates the 1st Law of Thermodynamics.

Mars escape velocity: about $5000 m/s$

$T = 0.5mv^2$ gets us about $10^7 J / kg$

Side-note: latent heat of vaporization of water is about $2\times 10^6 J/kg$, so all the water is going to start as water vapor. We get this energy back if the water condenses back to liquid again.

Mars is small, let's give it 1/10 the oceans of Earth. Earth's oceans mass about $10^{21} kg$, so we're giving Mars $10^{20}kg \times 10^7 J/kg = 10^{27}J$. We want to keep all of the water, turn it back into liquid, and reject most of the excess heat, so it must radiate this in $10^2$ years, for $10^{25} J/yr$.

Side-note: it's okay if some of the water gets away, since any molecules that leave take their energy with them and we're only concerned with energy balance at this point. We'll just need (lots and lots and lots of) extra water to pay for the water vapor atmosphere that leaves.

This is about 10 times as fast as Earth dissipates energy, with about 1/4 the surface area of Earth, so if we don't air condition the planet, following the Stefan-Botlzman law, Mars would have to be about $(10/0.25)^{1/4}$ times Earth's absolute temperature, plus a bit for what it gets from the sun, or a toasty $700K$. (It wouldn't be that, because rejecting all the heat in 100 years is an artificially imposed constraint, not a derived rate, that's just how hot it would have to be if it was going to cool down enough for liquid water at the end.)

So the question of how to get the water to Mars at all is entirely secondary to the question of how we build and power an air conditioner the size of a planet to radiate 40 times as much power as the whole planet it's based on/near. If we can't solve that problem first, there's no point bringing the water.

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  • $\begingroup$ This sounds like it's a Frame Challenge. If it is, it's desirable to state that in your answer. Thanks. $\endgroup$
    – JBH
    Dec 20, 2022 at 20:09
  • $\begingroup$ So he needs a wormhole, basically, or a teleporter. I hadn't considered the problem of how much it would heat up the planet, raining a whole ocean on it. But it really just changes the scale of the Treknology he needs to make it plausible. $\endgroup$
    – JamieB
    Dec 20, 2022 at 22:47
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I think you're asking too much for a "real" answer, but here's my off the cuff attempt:

Capture comets (or very icy asteroids) and throw them at Mars.

I would think the plan would be to capture anything you can find in space with a high water content and then send it into Mars orbit, and then, perhaps, just kind of blow it up so that Mars gets struck with a huge number of small, icy particles (to avoid any really devastating impacts -- we might not care about the damage but I'm betting single, large impacts would make a mess of the atmosphere for decades while we wait for the dust to settle).

It might just not be feasible, though.

A quick google check suggests there might be 400 billion gallons of water in near-earth asteroids. Lake Erie has 5.2 trillion gallons of water. Finding enough water to cover Mars with is going to be quite a task. We can probably get enough from the Oort Cloud but that's really far away. Extracting water from any planetary body / moon (e.g. Europa) would be exceedingly expensive, to get it out of the gravity well (of Europa, and Saturn).

(also, P.S. from your other question, 1 ton of water = about 240 gallons. Water is heavy. You need to be moving millions of tons of water at a time.)

So it really depends on what tech level you want to invent.

Is this Star Trek? Probably no problem then. Pop over to the Oort Cloud, find some big honking ice balls (we don't know for a fact that these exist but it's a plausible assumption) and tractor beam them over to Mars and start the transfer to the surface. Really if your world is 500+ years in the future you can just hand-wave it and figure we can probably go really fast and maneuver large objects into place.

If it's 50-100 years in the future, I'd say "no way", barring the invention of some fantastic new technology, or getting our hands on some alien tech.

("And inside the derelict space ship, humanity found something amazing: the key to anti-gravity and inertial nullification...")

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    $\begingroup$ As an example, Halley's comet has an aphelion in the near Kuiper belt (much closer than the Oort cloud, but full of known ice-balls) and a period of 75 years...so it'll take about that long for a spacecraft to go out to a Kuiper belt object on a minimal-energy trajectory and kick it back on a similar trajectory to the inner solar system. You've used up 3/4 of the time budget just getting there and back. $\endgroup$ Dec 20, 2022 at 16:00
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Five Minutes

Mars has an orbit about 1.5 times the size of Earth. As we learnt in school, Earth is 8.5 light-minutes from the Sun. So if the planets align it takes light 4.25 minutes to get from Earth to Mars. Your ocean of water takes the same time to make the trip at light speed. Since lightspeed is the fastest speed there is, the trip will always take 4.25 minutes or more. Let's round the 4.25 up to 5 minutes to account for speeding up and slowing down time.

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  • $\begingroup$ The question is: what it the fastest way to then give Mars a sizeable ocean of about 50% water cover? That seems to be asking for a procedure, not a time. Am I wrong thinking you might have done what I originally did and thought it was a duplicate of the OP's former question? $\endgroup$
    – JBH
    Dec 20, 2022 at 20:06
  • $\begingroup$ @JBH This answer is a cheeky way of me saying the question cannot be answered. The background is not specified. If the background is the real world then the problem is impossible. If the background is something else then the answer depends on that something else. $\endgroup$
    – Daron
    Dec 20, 2022 at 21:19
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I imagine you'd need to employ our good friend handwavium in such mass that you might as well not explain how you did it.

Space fold. Since we're just making things up. Effectively no different than what John O said several hours ago. If you have a source and you can somehow open a rift that allows you to drain an ocean from planet X to your new planet... while avoiding whatever catastrophes that surface from your violent dumping of sea water filled with who knows what directly into a planet that has not been prepared for this delivery. Factoring what might come about by the weight of this delivery and what the surface reaction would be. You might need all 100 years for the planet to calm down even if your initial delivery only took a few months. You might end up with some rich soil from all the dead life that was thrown into shock from the transplant. Or just a planet of total toxicity.

You might have better luck running with the idea that an underground ocean already existed there and it was discovered to be obtainable and usable as it was, without it having to be in surface sea form as we have on Earth. If it were kept underground, you might have less to factor about how the vast open sea interacts with the environment to cause weather. You would also have a very rich criminal empire that controls the viable holes deep enough to access this reserve, including whatever other handwavium you need to explain the conditions and usability of this underground resource.

In the end, I personally wouldn't try to explain this one. I might reduce it to a generalized term like "Water farm" and never explain how it is being generated. If you over-explain, you end up in Battlefield Earth realms where the science fiction is just too hokey to even allow yourself to suspend disbelief.

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