Hopes that man could set up lunar bases by exploiting the ice that is left behind by smashed comets and asteroids may be dashed. Research now suggests the Moon has little usable water.
Futurologists had believed there might be plentiful ice on the Moon that could be mined to support human life. Surveys by a Nasa spacecraft in 1998 suggested there was between 11 million and 330 million tons of ice dispersed across about 25,000 square miles at the satellite's poles.
However, a team from the Smithsonian Institute in Washington has carried out radar surveys of craters that never see sunlight and should be the ideal place for ice to gather. They found, disappointingly, that any deposits must be in the form of "distributed grains or thin layers".
The research, published today in the science journal Nature, does not put a figure on the amount - although the dispersed nature of any ice would probably put it at the lower end of the 1998 estimate.
Having water already on the Moon would simplify the process of building a base, because it is so expensive - in rocketry terms - to transport water from the Earth. It is virtually incompressible, and every kilogram of water carried from Earth will use up many times its weight in rocket fuel, as well as pushing out other important items.
Dr Ian Crawford, a lecturer in planetary geology at Birkbeck College in London, said: "Water is useful for three reasons: you need it to drink, you can split it using electrolysis powered by sunlight to get oxygen to breathe, and you can recombine its hydrogen and oxygen to create a rocket fuel. Any water at all is extremely helpful if you're setting up a Moon base."
The researchers used a radio telescope based at the Arecibo Observatory in Puerto Rico to observe what sort of signals bounced back from the bottom and the edges of craters on the Moon, and compared those with signals from craters on Mercury that are thought to have thick layers of ice.
But whereas the craters on Mercury gave one form of reflected signal, those on the Moon did not, even using wavelengths that could probe several metres down into the lunar dust.
"Thick deposits of ice ... are not observed within the crater floors visible to the Arecibo system," note the researchers. The only way that could be true, while also confirming results from Nasa's Lunar Prospector mission - which in 1998 detected the presence of ice by the scattering of neutrons - is if the water ice is present as grains amid the dust, or in thin layers.
Dr David Rothery, of the Department of Earth Sciences at the Open University, said: "I would have been very surprised if there were large sheets of ice. This finding does make colonisation of the Moon that much harder. You could extract it; it's still feasible to get water on the Moon if you want it badly enough."
Dr Crawford said: "It would be better if there was a lot of ice, but even if it's present at just 1 per cent, then by taking 100 kilograms of lunar soil and heating it to 100C, you'll get 1 kilo of water as steam. We could have a small base with a handful of people; they wouldn't need much water."
He insisted there were still important reasons, both scientific and political, for setting up a permanent Moon base. "Most contemporary planetary science is built on the legacy of the Apollo programme from more than 30 years ago," he said.
"And there are geopolitical reasons to go again - we need something that would unite us. Plus, when there's a space race on, then the arms manufacturers tend to make spacecraft rather than arms - and that's got to be a good thing for all of us."Reuse content