Why doesn't the ice in a comet just vaporize in space?

Answer 1

Because space is very very cold! The comet's tail is composed largely of vapourised ice (not necessarily H20) and rock debris. The ice is only vapourised when the comet passes past a star - hence why the tail is always directed at the sun (in the case of our solar system)

Answer 2

For the same reason that metal doesn't. Ice is a solid, and as such the interactions between the molecules are pretty strong. They're packed tightly together, at least when compared to water or gas. So simple intermolecular forces are sufficient to keep the thing together.

But when it comes down to it, comets *do* vaporize. As solar radiation heats up the surface of a comet so that the ice begins to melt, it vaporizes, creating the characteristic long tails occasionally visible from earth. But as space is rather cold, it requires an external heat source to melt the ice to the point that the water molecules are no longer tightly bonded to each other, and are blown away into space.

Answer 3

Because it's too cold.

When the comet is near the sun, part of the ice evaporates. This is what we see as the comet's "tail". The name "tail" might suggest that it is behind the comet relative to it's motion, but that's not the case. The tail points away from the sun because of the sun wind (radiation from the sun).

So every time the comet is near the sun, it looses mass. Eventually it disappears.

Answer 4

The above is a good answer with one correction .. the comets tail always faces AWAY from the sun as it vaporises.

Answer 5

Because the temperature in space is well below freezing. There is nothing- no oxygen or heat- to melt the ice.

Answer 6

maybe, cuz it's colder in a comet.

Answer 7

No friction