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Farmer
2003-Sep-26, 06:54 AM
How come the moon’s gravity is too weak to hold onto water molecules but strong enough to cause the tides on earth?

Haglund
2003-Oct-06, 08:16 PM
My guess is that the gravity is too low, but also that the moon doesn't have an atmosphere, which means it can not hold water as liquid. It will either vaporize into space when the sun is shining onto it, or eternally be in the form of ice if it is in a shadow. Anyone else have any thoughts on this?

kashi
2003-Oct-07, 12:00 AM
Welcome to the forum farmer.

You're spot parker. Gravity has nothing (directly) to do with it. Because there is no atmosphere (and therefore zero air pressure), liquid water would evaporate instantly. If this weren't the case then there could be plenty of liquid water on the surface of the moon. This is also the case on Mars, which has an atmosphere many times thinner than Earth's. Furthermore, this occurs on Earth with Carbon Dioxide, which sublimes from a solid to a gas as the air pressure is too low for CO2 to exist in a liquid state. Liquid CO2 no doubt exists on other planets with thicker atmospheres.

Kashi