Yes, in the form of ice. It has ice at its poles, at least excellent evidence for it. Probably mixed in with the regolith. It also has caves, and the ice might well collect in the caves. When comets and asteroids hit the Moon, then some of the ice in the comets would melt and boil to form a temporary atmosphere of water vapour which would then condense and collect in the colder regions of the Moon such as the caves and the craters at the poles. So that's one possible theory of how it got there.
Or could be through solar wind processing. It could also come from dense interstellar clouds, from time to time when the solar system passes through one that is sufficiently dense. Or from the geotail of the Earth - water from Earth can end up on the Moon at times when the Moon passes through the water vapour trailing away from the Earth.
There's a small amount of water in the rocks themselves. The Apollo astronauts only explored a small area of the surface of the Moon, mainly equatorial regions. And they couldn't drill deep below the surface. Some think there may be a lot more ice on the Moon in the subsurface, not just in the permanently shadowed craters in the poles, though this is a minority view at present.
If there was ice on the surface in sunlit regions, it would melt in daytime, and then evaporate and be lost to space - the boiling point of water goes down as the atmospheric pressure goes down. When it's a vacuum, then even ice sublimates into space. So the ice doesn't even have to reach O C, it would get lost anyway unless the rock stays very cold permanently.
So - if there is ice on the Moon it has to be in some place where the ice is very cold, so it doesn't sublimate, permanently sheltered from the sun. So that just leaves those three places - underground, at the poles in permanently dark craters - or in caves.
Theoretically - if it was underground, just a short way below the surface, and totally trapped - it could melt into a liquid without escaping, because it couldn't evaporate (it must be open to the vacuum in some way or another to evaporate). Hard to see how that could happen though. Perhaps if it was trapped by tarry organics, in ice originally mixed in with organics?? That's just a thought, not a serious scientific hypothesis :).
So, anyway, you can't really go so far as to say that liquid water is totally impossible on the Moon, because trapped ice could become liquid when heated by the sun in daytime. But it would require remarkable and unlikely conditions for it to occur. I don't think anyone expects to find any permanently liquid water there, even droplets of water.
Apart from that, it's going to be ice.
The ice is of special interest for several reasons
This is one idea for a lunar cubesat to look at the ice close up from orbit, which has been approved for one of the cubesats to be launched along with the main payload for the first test of the Space Launch System
Tiny Cubesat Will Hunt for Water Ice on the Moon
There's also a UK mission proposal to explore the lunar ice, Lunar Mission One, which did a kickstarter, which was a success. But early stages yet, their idea is to fund it partly by people who pay for it to deposit a strand of hair, or digital data, or both, into a time capsule to be left on the Moon at the end of the mission.
As for the idea that there is ice elsewhere beneath the lunar surface, Professor Arlin Crotts of Columbia University is a proponent. He thinks there may be ice even at equatorial regions at a depth of about 5 meters (far deeper than any of the Apollo missions could drill, the deepest they drilled was three meters). He thinks that it is possible that there are buried layers of water in the Moon also. For instance if the early proto Earth had a satellite which got incorporated into the forming Moon, then it might have brought water with it.
If he is right this would of course be of major importance for human spaceflights to the Moon. But his seem to be a minority view at least at present.
You can read about his ideas here: Water on The Moon, II. Origins & Resources -
and listen to him talking about them here: Dr. Arlin Crotts, Monday, 2-16-15 on David Livingston's "The Space Show"
Or could be through solar wind processing. It could also come from dense interstellar clouds, from time to time when the solar system passes through one that is sufficiently dense. Or from the geotail of the Earth - water from Earth can end up on the Moon at times when the Moon passes through the water vapour trailing away from the Earth.
There's a small amount of water in the rocks themselves. The Apollo astronauts only explored a small area of the surface of the Moon, mainly equatorial regions. And they couldn't drill deep below the surface. Some think there may be a lot more ice on the Moon in the subsurface, not just in the permanently shadowed craters in the poles, though this is a minority view at present.
If there was ice on the surface in sunlit regions, it would melt in daytime, and then evaporate and be lost to space - the boiling point of water goes down as the atmospheric pressure goes down. When it's a vacuum, then even ice sublimates into space. So the ice doesn't even have to reach O C, it would get lost anyway unless the rock stays very cold permanently.
So - if there is ice on the Moon it has to be in some place where the ice is very cold, so it doesn't sublimate, permanently sheltered from the sun. So that just leaves those three places - underground, at the poles in permanently dark craters - or in caves.
Theoretically - if it was underground, just a short way below the surface, and totally trapped - it could melt into a liquid without escaping, because it couldn't evaporate (it must be open to the vacuum in some way or another to evaporate). Hard to see how that could happen though. Perhaps if it was trapped by tarry organics, in ice originally mixed in with organics?? That's just a thought, not a serious scientific hypothesis :).
So, anyway, you can't really go so far as to say that liquid water is totally impossible on the Moon, because trapped ice could become liquid when heated by the sun in daytime. But it would require remarkable and unlikely conditions for it to occur. I don't think anyone expects to find any permanently liquid water there, even droplets of water.
Apart from that, it's going to be ice.
The ice is of special interest for several reasons
- It may preserve evidence of the history of the solar system - one layer on top of another for billions of years - like the Antarctic ice cores. Preserving gases, and even organics
- Some think it may also have meteorites from Early Earth - if so could have organics from Early Earth too - but you'd have to dig to find them.
- Possible source of liquid water on the Moon for human astronauts there
- Some think it might some day be economic to export it to use in LEO and elsewhere for rocket fuel (which you get by splitting the hydrogen and oxygen in the water) - and to create oxygen for humans to breath.
This is one idea for a lunar cubesat to look at the ice close up from orbit, which has been approved for one of the cubesats to be launched along with the main payload for the first test of the Space Launch System
There's also a UK mission proposal to explore the lunar ice, Lunar Mission One, which did a kickstarter, which was a success. But early stages yet, their idea is to fund it partly by people who pay for it to deposit a strand of hair, or digital data, or both, into a time capsule to be left on the Moon at the end of the mission.
As for the idea that there is ice elsewhere beneath the lunar surface, Professor Arlin Crotts of Columbia University is a proponent. He thinks there may be ice even at equatorial regions at a depth of about 5 meters (far deeper than any of the Apollo missions could drill, the deepest they drilled was three meters). He thinks that it is possible that there are buried layers of water in the Moon also. For instance if the early proto Earth had a satellite which got incorporated into the forming Moon, then it might have brought water with it.
If he is right this would of course be of major importance for human spaceflights to the Moon. But his seem to be a minority view at least at present.
You can read about his ideas here: Water on The Moon, II. Origins & Resources -
and listen to him talking about them here: Dr. Arlin Crotts, Monday, 2-16-15 on David Livingston's "The Space Show"
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