Having very little to say about the events of this comic, I thought I'd say something about the process, at least as I understand it.

You're going to try to squirt the water into space. The cost of launching kiloton after kiloton of water is going to add up. Even with a space elevator, the amount of electricity needed to send that much water up at a high enough velocity that it goes out of the planetary's gravity well... well, gravity sucks.

Okay, so this is Sufficiently Advanced Technology. You have two choices. Choice one: give it some angular momentum, and let the mass turn into a moon. Big benefit number one: your center of mass stays the same. Choice two: give it even more energy, so it is no longer bound to your planet, but is bound to the star instead. If you really wanted to hide a water planet, having it be a water moon would be a really good way to do it.

Alright, so you have all this big mass of water sent out in space. Enough water that its gravity starts to pull it together. It's out in the coldness of space, so it's going to try to radiate heat. If it was able to radiate heat out, it would cool off, and then freeze. And freezing water does strange things. The two biggest ones are, of course, (A) it floats, and (B) it gives off heat.

(B), it gives off heat, is the odd one. I was surprised to find out just how much heat is given off by freezing water. It's actually enough to melt nearby water. It's enough to support microscopic life. But space is a wonderful insulator. It's hard to radiate out that much heat (see Coruscant discussion). So your water is going to be under high pressure, without being supercold.

High pressure will force things into a solid state, by forcing the molecules together, and not giving them enough room to move freely. The free movement of molecules is pretty much what defines a liquid; high pressure restricts that free movement. But now we get into the odd thing about ice. Ice isn't water molecules tightly packed. The reason water expands when it freezes, is that the water molecules arrange themselves into rings with a gap in the middle. When you have high pressure, you can have the water unable to move freely, and not be in that ring shape.

Unfortunately, that's about where my knowledge of the different stages of ice ends. From what I understand, there's something like 10 different types of ice, with different physical properties corresponding to different levels of pressure, temperature, etc. (Whether or not the ninth stage is actually a grey goo or not will be left to books.)

So what will this big mass of water under its own pressure wind up looking like? Well on the surface, you have ice that hasn't been able to radiate off heat, at normal pressure. That's water. So you have a layer of water on the surface. As you go deeper, the temperature may rise if the sphere is contracting under its own gravity (or maybe not if it's just super-scienced into place). But the pressure will be high enough to generate the oddity of exotic ice phases at temperatures above freezing.

Will this mass be spinning? It probably will be. It will be hard to put all of that water into space perfectly aligned at its center of mass all the time. There will probably be some spin. So you have the center, solid under pressure with one spin rate, and the water liquid possibly with a different spin rate. It should essentially equal out, but you can expect nasty storms until it does. And since we are talking about a relatively short amount of time, it should still be stormy there right now.

Especially if they tried to dump a large pile of sand on top of the solid center, and are somehow hoping that sand won't be blown around the planet by the waves.

Alright. So far, this seems to be pushing the bounds of plausibility. But now we have one bigger problem.

Solar wind. Magnetosphere. Lack of magnetosphere. Presence of solar wind. That water is not going to last. Living on that ball of ice water is not going to be pleasant. In fact, the best way to be shielded from the solar radiation is to live under the water.

Imagine a giant bubble, designed to be denser than the surface water, but not as dense as the deeper water, floating down about halfway down the water. (Okay, maybe not quite that deep; The bends might be a problem.) Kind of like a giant bubble floating on top of a gas giant. That will give you the shielding from the radiation, hiding from enemy scans, and even some protection from the surface ocean waves.

Ten quatloos says that the movie did not go to this much thought on the issue.

— Keybounce