On Thu, 11 Nov 1999 you wrote:

> A student asked what would happen if your space capsule strung a pressure
> leak. I replied that among other things, anything that contains water would
> flash boil due to low pressure, even at a very low temperature. But, upon
> reflection I wasn't so sure. How about the hope for water ice at the lunar
> poles? The temperature is very low, but so is the pressure. Even if water
> ice had ever been at the lunar poles, wouldn't low pressure have allowed that
> water to sublime away long ago?
> Any help much appreciated.
> Dave

Hello,

You are right that, in sunlight, any ice exposed to the sun would heat up
enough to sublimate away. Therefore, most of the moon is totally devoid
of any traces of water. But there are craters on the moon that never see
sunlight - these craters are at the moon's poles, where the temperature
remains cold enough that frozen ice will not sublime. So, if water were
to be delivered to the moon by the impact of a comet, water could still be
found on the moon.

Information on the first detections of water from the moon can be found at
a NASA web page:
http://nssdc.gsfc.nasa.gov/planetary/ice/ice_moon.html

Thanks for writing!

Sincerely,
Kurtis Williams

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