comet formation

[Stevil]

i know this may seem like a simple question, but i would like to know:

if things boil at low temperatures in space due to the low pressure how do comets form? wouldn't the water boil, rather than freeze? wat about the ice around saturn?

if i were to shoot water out of a spaceship would it freeze or boil?

 

thanks

[YT2095]

comets aren`t made of just water, they contain other gasses with a lower boiling point troughout their mix, as these gasses boil off (evaporate) that has a cooling effect on the other materials with a higher boiling point, such as water or carbon dioxide. this help to keep their shape and also propel them along as the ejected gasses work a bit like a rocket thruster.

[[Tycho?]]

Hmm, I've never thought of that before, good question.

[Glider]

if i were to shoot water out of a spaceship would it freeze or boil?

 

thanks

It would try to do both at the same time. It would boil due to the vacuum, and it would lose heat rapidly. If there was enough of it, whatever didn't boil off before it reached freezing temperature would freeze solid.

[Martin]

... wat about the ice around saturn?

if i were to shoot water out of a spaceship would it freeze or boil?

:

 

It would depend some on how far the spaceship was from the sun

 

 

(as well as how much water and what temp it starts out at)

 

 

ice can exist in a near vacuum as long as it is in the shade

or far enough from the sun

 

several of the moons of jupiter are known to have icy crusts

(some are believed to have liquid water deep under the surface)

 

it is believed possible that some ice might exist in craters at the north or south ends of the earth's moon because there would not be enough sunlight and heat radiation to warm it up

conditions in a crater at the lunar north pole would resemble those on a colder body more distant from the sun

 

Here is what I picture happening, maybe someone else can make this more precise (it depends on equilibrium temperature and vapor pressure at that temp, so is a bit technical)

 

A. if the spaceship were at Venus' distance from the sun and you gently squeezed a glob of cold water out into space

then you could watch it simultaneously boil and freeze for a while

until there was only a remnant consisting of ice

 

but the chunk of ice would not last because it would be close enough to the sun that the sunlight would warm it, and it would evaporate

 

B. if the spaceship were at Saturn's distance from the sun and you gently squeezed a glob of cold water out into space

then you could watch it simultaneously boil and freeze for a while

until there was only a remnant consisting of ice (just like in the other case)

 

but this time the ice-chunk would not appear to evaporate. It would seem to be permanent because it would be far enough from the sun that its equilibrium temperature would be very low

it would be so cold that its vapor pressure would be negligible