The BBC's Simon Jones reports on a blazing end to the mission

The space agency said Lunar Prospector landed on target, deep within a lunar crater near the Moon's south pole.

Nasa is hoping the impact, calculated at 6,000 km/h (3,800 mph), has sent up a plume of water vapour from what are believed to be ice formations near the pole.

So far there has been no direct sighting of debris and observatories around the world are watching to see if any ice was melted, generating water vapour.

"Initial reports indicate that no plume was visible at the expected impact time," said a Nasa spokesman.

Close-up of the impact point

The discovery of water on the Moon could open the way to future lunar exploration and even the establishment of a lunar base.

A secondary mission for the spacecraft was to deposit the cremated remains of the renowned astronomer Eugene Shoemaker, making him the first person to be buried on another world.

Cautious optimism

Toby Murcott of BBC Science: "The discovery of water could open the way to future lunar exploration"

Nasa scientists were wary of being too optimistic that they would hit the right part of the moon.

"This is a low probability of success," said Dr Lisa Chu-Thielbar, a Nasa spokeswoman. "In fact its been calculated at about 10% success."

"But it's still worth doing because the possible result is terrific."

Nasa insists that regardless of the outcome of this "final bold experiment", Lunar Prospector has yielded "a gold mine of science data".

"We now have invaluable global maps of the Moon's gravitational and magnetic fields, and the distribution of its key elements, giving us a much better understanding of the origin, evolution and composition of our rocky neighbour," said Dr Henry McDonald, director of Nasa's Ames Research Center.

'Outstanding mission'

After its launch in January 1998 and subsequent entry into orbit over the lunar poles, instruments on board the Lunar Prospector began surveying the Moon.

Among its discoveries:

• Tentative evidence of ice in permanently-shadowed craters near both poles
• The first precise gravity map of the entire lunar surface
• Confirmation of the presence of local magnetic fields that create the two smallest magnetospheres in the Solar System
• The first global maps of the Moon's elemental composition

Shoemaker honoured in death

The "burial" of one ounce of Eugene Shoemaker's ashes is a rare honour accorded to a member of the space community.

Mr Shoemaker co-discovered the comet Shoemaker-Levy 9, which collided with the planet Jupiter in 1994.

The renowned astro-geologist, was killed in a car crash two years ago.

"He is the very first human inhabitant of Earth to be laid to rest on another celestial body," said Carolyn Porco, a University of Arizona professor and Shoemaker's college on Nasa's Voyager expeditions.

"That's very significant because it says we have arrived at our place in the solar system, the solar system is our own and it's beckoning us."