The predictions of Walt Brown

JonIt would certainly radiate heat pretty fast. The main reason for this ,however is that all of the molecules would space themselves out as far as possible in an attempt to fill up all available space. That's what happens to a liquid in a vacuum. (Basic pressure laws.) This makes the surface area/volume ratio of the water vapour much larger that for liquid water so it will be much more efficient at radiating heatNo ice will ever be formed as water ice is not possible in a vacuum at any size greater than a single H2O molecule. While it is possible that these molecules might fall back to earth, they will do so very slowly and over a long periodTrouble is that this heat radiates and conducts a whole lot quicker into the atmosphere than into vacuum so most of the heat would be lost before it ever got to space. Also any huge gust of vapor pressure going up that fast will tend to drag an enormous amount of atmospheric gasses with it into space. This atmosphere is either going to come back down as super heated gas or be lost to space forever. (I think most will be the former)Ether way you are right that he is damned if he does and damned if he doesn't. It's just that even if they do have enough energy to reach space (highly unlikely that that is)then they are still gonna fry everybody by conductive heat transfer long before they get there.PY

Ever tried actually doing that?I have. It doesn't happen that way.I work with vacuum systems every day of my life.I also fire super heated water vapor (7000K) into a vacuum system every day of my life. There has never been any ice formed in it.Check out this phase diagram of water. It clearly shows that water can normally only exist in the vapor phase in a total vacuum.
I was surpised at how amazingly difficult it was to find a decent phase diagram of water. There are a lot of these phase diagrams out there on the web but most of them don't go anywhere close to a vacuum on the Y axis so they look as if water can exist as a solid under these conditions. The only way to get solid water ice in a vacuum would be to get the temperature down close to absolute zero. You also have to remember that space in our Solar System is actually quite hot unless you are in the shade of a planet.If you pull a hard enough vacuum on a block of ice, it will rapidly sublime into the vapor phase unless you can simultaneously cool it way down near to absolute zero.
If you pull a vacuum on liquid water it will boil into the vapor phase. It will never form ice. I don't know where you got that peice of information from but it is wrong.As for Pluto, it is mostly made up of frozen Nitrogen, Carbon monoxide and some methane. There is no water ice there.Comets? I must admit here that I find a lot of references to water ice in these, but even then there is none on the surface according to this news bulletin from Nasa's Jet Propulsion Lab.
I can only assume that the water ice is protected from the Sun's heat by the surface layers.PY

Yes that kind of confused me a little too. I have no idea what is going on there really. Maybe some kind of localized pressure increase from the mass of the comet?
I wouldn't have thought 100kms diameter would be enough to generate much gravity though.PY

Hi CoryagypsJust been thinking a little about your beaker in a bell jar experiment and I can see why it would tend to freeze the water. I think what you are seeing is that the surface of the water rapidly boils off as the pressure drops. In order to change phase it draws energy from the surrounding water, thus making it colder. This works like refridgerant in a freezer and is obviously going to cause the surface of the water to freeze. However if you leave the bell jar under vacuum in your lab for a day or two, there will be no ice left as it will all sublime away. The fact that the bell jar is at room temperature will provide it with plenty of radiated energy to do so.Now try doing it with a jet of super heated steam. It is already in the vapor phase with all its molecules well spread out so it will never condense to form the solid ice in the first place.
I do this all the time with an ICPMS. (Inductively Coupled Plasma Mass Spectrometer) We pump gallons of water into a hard vacuum at very high temperatures and no ice has ever formed.Here is a possible explanation for how comets can contain water ice. The solid ice cannot actually sublime without an input of energy to help it to change phase so at close to absolute zero, as it most likely is out in the Ort cloud, even though the ice would be more stable as a vapor, there simply isn't enough available heat to allow it to change phase.Your data sounds fine except that 1.0mm of mercury (1 Torr, 1.33 miliBar or 0.0013 atmospheres) is still a pretty high pressure. You are 8 orders of magnitude (or more) too high here.
Try looking up 5E-8mBar or 3.5E-8 mm of Mercury. That is the vacuum that I work at and it is much closer to what you will find in space.Actually I am not really sure what the actual pressure in space really is but everything I can find about it assumes a pressure of near to zero. It is possible to reach 1E-10 mBar in a high vacuum mass spectrometer so I should think space was around that level. Here is a useful site to convert pressure from one unit to another.Incidentally, we use some Platinum components in the high vacuum systems and they do sublime quite rapidly. We lose a seal (5 G or so) about once per year. Bear in mind that it also has a very small cross section that is exposed to the vacuum. Gold dissapears even faster. A gold coin the size of a quarter would be entirely sublimed in less than a month. (I haven't actually tested this due to the cost of the experiment) We used to use gold seals but they didn't last long enough to make it finacially viable.PY

Coragyps - Yes I think you are right that the vacuum in space is somewhere like the best that we can achieve on the ground. That means we have to assume around 1E-10 mBars or better. It isn't easy to find data on systems that low.Your bell jar is probably powered by a single stage rotary vane pump. Right?I use two twin stage rotary vane pumps as the backing pressure (about 2E-2 mBar) for a bank of 3 turbo molecular pumps in order to reach these very low pressures.PY

The stuff that sublimes off is what makes the tail that always faces away from the sun. (following the solor wind)[speculation] I guess comets must continuously get smaller with each circuit. The only thing saving them is that they spend a vast majority of their lives out where the sun's radiation is too small to give the ice that little bit of energy that it needs in order to change phase. [/speculation]FYI I really know bugger all about comets.PY