Well, not very wet. One ton of moon dirt might have enough water to fill a couple of beer or soda cans.
But three orbiting Lunar satellites have independently confirmed the presence of water on the Moon. You would find higher quantities of water in the sands of the Sahara on a midsummer day.
But it's there. Splish splash. Water. On the moon.
In eighth grade science, we were taught that water would boil away immediately in a vacuum. We assumed that it would turn into steam and drift up and away, the way steam does in the kitchen.
Of course, what we see isn't actually water vapor. Visible steam is water vapor that is cooling and condensing back into tiny water droplets, which, in a group, are visible to our eyes. Water vapor is invisible.
And the reason it is rising is because it is less dense than the air, and thus lighter. A helium balloon rises for the same reason, but on the Moon it would fall at the exact same speed as a rock, despite weighing only one sixth as much. No atmosphere to be lighter than.
So let's say a comet hit the Moon (and it's safe to assume that quite a few have over the past 4.5 billion years). Comets are mostly frozen water vapor, technically known as “snow.” Most of the comet splashes off in all directions not impeded by the Moon itself, much of it hard enough to escape the lunar gravity and go make a nuisance of itself somewhere else. The stuff that doesn't falls on the lunar soil. It doesn't float because there's nothing to float in. Let alone rise. During the Moon's 28 day “day,” it's frozen water vapor during the roughly 338 hours of night, and gaseous water vapor during the day. But aside from some very subtle Brownian motion caused by the conversions from ice vapor to steam and back, it doesn't move at all. So vacuum notwithstanding, the water doesn't “boil away,” but just sits there. Any water that lands on the moon stays on the moon. The molecular motion in steam doesn't exceed 2.38 km/s, which is what it takes to escape the Moon's gravity. It doesn't come within three orders of magnitude of that.
That water is there to stay.
If the Moon is ever so slightly damp, Mars is sodden.
Mars might actually have more fresh water than Earth. (Only 2˝ % of the Earth's water is fresh, and a lot of that, like Mars' water, is frozen).
Just a year ago they were conjecturing that there might be as much fresh water on Mars as is contained in the Great Lakes, but since then, they've discovered that you need only dig a couple of centimeters into the soil in many places to find pure ice that might run several kilometers deep.
Last summer, the Phoenix Mars Lander dug a little trench, and photographed a bright substance on the bottom. Several days later much of it had gone and scientists realized it was ice. Then, last week, the Mars Reconnaissance Orbiter (MRO) doing a survey of five recent meteor strikes in the temperate latitudes of Mars, discovered ice patches subliming away (but not out of Mars' gravity well!) in all of them.
Ice is common under the Martian soil, only centimeters or meters below, and extends well away from the polar regions. The five impact craters the MRO examined were at about 45 degrees latitude, half way between the pole and the equator.
The BBC wryly noted that had the Viking craft that landed on Mars in the mid 70s been able to dig just a few centimeters deeper, they would have almost certainly have found water. But they didn't, and we spent a rather dispirited two decades believing that Mars was as dead and sere as the Moon, totally bereft of water. While other factors definitely had a hand, including the loss in Vietnam, Watergate and the Pardon, and the coarsening of the culture, it's indisputable that Science Fiction got darker and less playful once the Vikings drove a stake through the heart of Barsoom. As one SF writer infamously remarked, “The future ain't what it used to be.”
Incidentally, the MRO page has some truly astonishing images of Mars. http://mars.jpl.nasa.gov/mro/
Here on Earth, we're heading in the other direction. Instead of unexpectedly finding more fresh water than anyone believed to exist, we've discovered that it's vanishing at an unexpectedly high rate.
The one getting the most press attention is the rate of decline of the Antarctic ice cap. First came the disturbing news that the rate of glacial melt along the edges of the continent was more than double the rate in the 1970s. Then came the news that laser measurements from satellites showed the icecap falling at the rate of a meter a decade. Granted, the ice cap averages about 3.5 kilometers deep, so at the present rate, it would last another 35,000 years. But the rate is expected to accelerate as the amount of CO2 increases.
Most interesting was the discovery, made by analyzing microfossils, that about 33.5 million years ago, the concentration of CO2 in the atmosphere dropped below 760 parts per million, and it was at that point the Antarctic ice cap began to form. Presently, CO2 is about 387ppm, well above the 290ppm in 1900, but well below the 1600ppm that it maintained during the Jurassic period.
The second cause of decline in fresh water is simply too many people. The Earth's population is near 7 billion, and this means that we are not only consuming water at record levels, we are wasting water at record levels. And since nearly 5 billion people have sewage and sanitation that ranges from inadequate to nonexistent, more of the water is getting polluted.
Agriculture takes its toll, since in many areas well water is used for irrigation, with the result that the water table drops faster than it can be replenished. Worse, the further into the water table they go, the more minerals in the water extracted, with the salts leaching into the soil, requiring more irrigation to get things to grow until the point is reached where the soil is just too saline to support plant life.
One result of global warming is that the weather patterns shift, with the result that areas that might get a lot of water are now parched, and areas that are hardpan are getting soaked. Unfortunately, the soils in the various areas don't maintain a similar rate of change to adapt to the changes in local climate, with the result that the amount of arable land will drop.
You may have seen the pictures of Sydney, Australia, looking like an outtake from Brendan Fraser's “The Mummy,” with a vast miasma of dust choking the city and turning everything orange. The outback, never lush, is having a record drought.
One global warming denier gleefully announced that the amount of iron oxide in the dust was adequate to replenish the world's oceanic supply of plankton, and that would end global warming forever. Honestly, they'll say anything. There is enough that if it gets into the south drift currents, it will trigger a population explosion of krill along the coast of Antarctica for a year or so, but that's about it. No cure for global warming in sight.
The good news is that overall, there is likely to be more rain, since evaporation is a function of heat, and the more evaporation, the more rain. And none of it will reach escape velocity, even with Brownian motion.
And, if the rains don't fall on land where we could use them, then I suppose we could all go to Mars. I hear they have lots of fresh water there.