[Sharlin]

Water does not stay liquid in a vacuum. It is either solid or gaseous, depending on the ambient conditions. It is not well established where the primordial Earth gained its water. The matter in the protoplanetary disc from which the Earth coalesced probably didn't contain much water or other volatiles because of the proximity to the Sun. Instead, it is thought that water arrived afterwards, via numerous collisions - then commonplace - with icy comets that originated beyond the frost line.

http://en.wikipedia.org/wiki/Frost_line_%28astrophysics%29 http://en.wikipedia.org/wiki/Origin_of_water_on_Earth

[lordlicorice]

Would a sphere of water that size be massive enough to hold a gaseous atmosphere heavy enough to allow liquid water far enough down?

[kijin]

With a diameter less than half of the Moon, and with a mass only 1/50 of the Moon, I think it's quite unlikely.

[guard-of-terra]

Volcanoes emit a lot of water aren't they? I've heard more than half of the emission is water vapor.