The water is out in space, a place we used to think of as
desolate and desert dry, but it's turning out to be pretty
lush.
Sure, if you want to use bullshit mathematics to get that "28 galaxies" number I guess you can make it sound impressive.
The amount of water in all the Earth's oceans is a miniscule proportion of the amount of water in the solar system, though. The Kuiper Belt, the Oort Cloud, the moons of the outer planets -- all these solid bodies are made up largely of water ice (mixed with ammonia and methane, plus a bunch of rock). The real wet spots of the solar system, though, are the giant planets themselves -- Jupiter, Saturn, Uranus, Neptune. Uranus and Neptune are ice giants, made up mostly of the water-ammonia-methane mixture that we lazy scientists just call "ice". Let's estimate it at something like five Earth masses worth of water in each planet. Jupiter and Saturn consist basically of huge seas of hydrogen-helium which accreted around an initial ice-rock core; a much lower share of their mass is water, but a good handwavey estimate would be something on the order of five Earth masses' worth of water in each of those, too. [Left out: a bunch of details and caveats.]
So we're talking roughly 20 times the mass of the Earth of water in the solar system. (The Oort Cloud, Kuiper Belt, all the icy moons, and the Earth's oceans themselves are a rounding error.)
Now, let's recompute. Total amount of water in this particular object is 140 trillion times the amount of water in all the Earth's oceans, which comes down to about 28 billion Earth masses' worth of water, or enough to form about five billion Neptunes. Latest estimates suggest that Neptune-like planets are extremely common, so there is almost certainly far more water in Neptunes just in our own galaxy than in this big cloud.
Still, quite a lot of water.
So nominally in a vacuum water sublimates into vapor, but at very low temperatures it stays ice. So you've got these icy bodies in the Kuiper belt which become comets when their orbits take them past the Sun. Typically, a comet is 'solid' but solar insolation causes it to evaporate/sublimate giving it the characteristic tail (correct me if I'm wrong here on this).
So what I'm wondering is, could you have a 'water' planet which was basically a blob of water surrounded by presumably a CO2/NO2 atmosphere? Could it be liquid all the way through or would its 'core' always be solid?
http://en.wikipedia.org/wiki/Triple_point
Edit: The center of the earth is 350gph and 5430°C water would probably be a liquid at that temperature and pressure but I don't think it's been tested. Still, a smaller planet could be possible and stable on the scale of a few million years. http://en.wikipedia.org/wiki/Inner_core
I'd say "probably", but answering that question definitively would involve breaking out some fancy planetary modelling techniques and looking at the phase diagram of water. Make it too small and it'll sublimate away like a comet, as you say. Make it too large (ie approaching Neptune mass) and the core will be in some non-liquid phase (either an solid or a non-molecular plasma type phase). I'd guesstimate there to be a decent range of values in between, though. Smaller than Earth with a thick non-water atmosphere? Might work.
Not only in proportion to the entire solar system, but also just in the context of our own planet. We think of Earth as a wet place because we keep hearing that two-thirds of the surface is covered in the stuff. But it's an incredibly thin coat.
At its deepest points the ocean is what, eleven kilometers deep? From there it's another six thousand kilometers to the core.
We're more a rock with a thin sheen of water than we are appreciably 'wet'.
There's a common misconception, incidentally, that the mantle is liquid.