Slamming a spent rocket booster into the frigid, inky shadow of a lunar crater last month sent up a plume of dust laced with water, NASA scientists reported in a press conference today. Observers on Earth were denied a view of the fireworks in October, but “we found water, a significant amount of water,” said LCROSS (Lunar Crater Observation and Sensing Satellite) mission principal investigator Anthony Colaprete of NASA’s Ames Research Center in Mountain View, California.

After several decades of controversy, scientists now know that over billions of years, water from who knows where–impacting comets or perhaps the solar wind–can collect in some of the coldest places in the solar system. Whether the predicted amount of water is enough to sustain future astronauts–as either sustenance or rocket fuel–remains to be seen, however.

The LCROSS mission worked to perfection, with the exception of the show that unfolded on Earth. Before the impact, NASA scientists had predicted that ground-based observers, even amateurs, would see the plume in the gap between two mountains. As it turned out, Colaprete said, the impact’s plume of debris “was as bright as thought, but it was behind a hill” because the debris did not rise as high as impact modeling had suggested.

The heavily instrumented LCROSS spacecraft, however, had a fine view of the rocket booster’s impact and aftermath as it sped to its own impact 4 minutes later. LCROSS instruments delivered a “good, strong detection” of water, Colaprete said. At infrared and ultraviolet wavelengths, they gave clear indications of water vapor, water ice, and hydroxyl ions produced when sunlight splits water molecules.

All told, LCROSS detected about 100 kilograms of water, Colaprete said. It came from a 20-meter-wide crater maybe 3 meters deep, but he declined to guess how abundant water ice had been beneath the impact site. Team members must still calculate what portion of subsurface ice actually rose into view and could have been measured, Colaprete noted. “It would probably be safe to say it’s wetter than the Atacama Desert,” the driest place on Earth, he said. Some remote sensing had suggested about 1% water ice by volume in the upper 3 meters, which was regarded as a substantial amount. Impact modeler and LCROSS team member David Goldstein of the University of Texas, Austin, says 1% “is not inconsistent with what’s been observed. I haven’t convinced myself yet whether it’s 0.1% or 10%. I think we’ll work that out.”

Whatever the amount, the principle of cold-trapping water in permanently shadowed craters–as had been demonstrated for Mercury using radar–is now firmly established for the moon. The LCROSS results give only an inkling of where the water might have come from. Colaprete reported that spectra hint at the presence of volatile compounds besides water, such as carbon dioxide, methane, sulfur dioxide, and methanol, just the sort of compounds found in comets and ice-rich asteroids. So the moon may have retained a tiny bit of the objects that have pummeled it for eons.

Scientists announced tonight that they have discovered “buckets” of water on the Moon following the analysis of data from a spacecraft that was deliberately crashed into a lunar crater last month.

The researchers said the evidence for the existence of significant bodies of water ice hidden in polar craters on the Moon is “definitive” and that the total quantities could be big enough to support a permanently-manned lunar base.

It is the first time that the US National Aeronautics and Space Administration (Nasa) has been so categorical about the discovery of water on the Moon. Previous studies had only suggested that the presence of water might be possible and then only in trace amounts.

However, a painstakingly detailed analysis of the data from the LCROSS spacecraft, which was deliberately crashed into the Cabeus crater near the Lunar South Pole, has revealed a definitive chemical signature of water vapour in the plume of dust and debris that was released on impact.

In just one crater, the team estimates that there was at least 100 kilograms of water, enough to fill a dozen, two-gallon buckets. If similar amounts of water exist in other polar craters permanently shaded from sunlight there could be enough water available on the Moon to be used as drinking water for a lunar base – or used as a source of rocket fuel.

Anthony Colaprete, the principal scientist of LCROSS (the Lunar Crater Observation and Sensing Satellite), said that the “eureka moment” came when the team saw a spectroscopic line indicating the presence of the OH water molecule, which could only exist if water was present in the crater.

“What we found was indeed water…We vetted it, vetted it, vetted it, vetted it and vetted it some more as a team…I’m pretty impressed by the amount of water we see in this small, 20-metre crater,” Dr Colaprete said at a press briefing from Nasa’s Ames Research Centre in California.

“It’s safe to say it’s not a frozen lake with a perfectly frozen surface. It was probably mixed in with the surface. It would be an interesting place to walk around,” Dr Colaprete said.

Mike Wargo from Nasa said: “We’ve discovered significant quantities of water in a permanently-shaded crater on the Moon. We’re not just talking of water on the Moon, but lots of water.”

When LCROSS was crashed into the Moon, it was expected to eject a visible plume of debris six-miles high that was supposed to have been visible from Earth. However, Nasa scientists said at the time that the absence of a visible plume did not mean that the mission was a failure.

Nasa’s Gregory Delory said that the discovery is one of the most exciting to be made in connection with lunar exploration. “If we find water in large enough amounts it could be used as a resource for human exploration,” Dr Delory said.

“Now we know there’s water there thanks to LCROSS we can go to the next set of questions. It’s a new picture of the Moon. It’s going to be a very exciting time,” he said.

One of the unresolved questions is how the water could have got to the Moon. One theory is that it arrived on a comet and never evaporated in the shaded polar craters where temperatures are minus 220C.

Another possibility is that the water arrived on a solar wind, which is a stream of ionised hydrogen gas. A third theory is that is was dropped by a molecular cloud, or dropped by ice-laden cosmic dust. It might even be terrestrial water kicked up from Earth in a gigantic asteroid impact.

Nasa estimates that there are 12,500 square kilometres of permanently-shadowed terrain on the Moon and if the top 1 metre of this area were to hold just 1 per cent by mass of water, this would still produce thousands of litres of water.

It is not the first time that spacecraft have crashed into the Moon. In 1998, Nasa’s Lunar Prospector mission was deliberately crashed into a crater, which confirmed the presence of hydrogen, which may or may not have come from ancient stores of frozen water deposited in lunar craters over billions of years by passing comets.

By Steve Connor