The presence of water on the Moon would make it feasible to set up a permanent settlement, which could then be used to develop and test the technologies to colonise other planets.
Ice could be melted to form drinking water, or electrolysed by solar power into hydrogen and oxygen for rocket fuel. Some estimates before today's announcement suggested that there could be a billion tonnes of ice at the poles.
Nobody at Nasa would comment on the rising expectations yesterday. But the space industry in the US has been buzzing for weeks about preliminary data from the Lunar Prospector spacecraft, which has been orbiting the Moon for six weeks. According to early leaks, the first data confirmed spectroscopic data from a US military mission four years ago. That indicated that ice exists at the poles, probably the remains of comets which crashed into the lunar surface.
The scientists in charge of the mission are understood to have been told to check their data, so that Nasa would not subsequently have to retract any announcement. But in the past few days, Nasa has issued a string of notices raising the profile of the mission and even offering live TV interviews with the scientists when the announcement is made at 10am in Florida today.
Earlier this week, Professor Alan Binder, who is leading the analysis of the data, told The Independent: "I'm not allowed to say what we have found. All I can say is that we have extremely good data, and we can't say whether there is or isn't water there."
But another source said: "The gossip is, from the preliminary results, the data would all be in keeping with water. Now they want the Prospector to go in closer to confirm it - even to crashland."