It was supposed to have been the dramatic climax of an ambitious space mission to find large bodies of frozen water on the Moon – a discovery that could accelerate the exploration of the solar system.
But Nasa scientists admitted yesterday that they were perplexed as to why the deliberate crashing of two parts of a spacecraft into a lunar crater failed to produce the predicted six-mile-high plume of debris that should have been visible from Earth.
The plan was to generate a cloud of ejecta from the crater that would carry any frozen water molecules buried in the permanent shade of its bed to the sunlight at its rim, where they could have been detected by the second half of the crashing spacecraft.
Everything went according to plan, with the spacecraft, called the Lunar Crater Observation and Sensing Satellite (LCross) dividing just prior to its collision with the Cabeus crater near the lunar south pole yesterday, about 12.30pm British time. The only thing missing was the visible plumes of dust as each part of the spacecraft hit the crater's base about four minutes apart.
Despite the apparent setback, Nasa scientists said that they were still able to carry out all the measurements they had expected to make. They are confident that if water was present in the crater, they will still be able to detect it with LCross's highly sensitive spectroscope designed to measure the electromagnetic emissions of the hydroxyl molecule of water.
"Everything really went very well, the spacecraft flew beautifully and the instruments performed better than expected. We've got interesting results," said Anthony Colaprete, the LCross principal scientist.
"There was an impact, we saw the impact, we saw the crater and we got the spectroscopic measurements. We have the data there to answer the questions we wanted to answer."
All three cameras on board LCross, including a thermal camera made by the British company Thermoteknix, monitored the impact with the crater. It began with the crash of the 2.2-tonne Centaur rocket – the empty upper stage of the spacecraft – followed a few minutes later by the impact of the smaller, instrument-packed probe of LCross after it was supposed to have flown through the debris plume.
Asked about the absence of a visible debris cloud, Dr Colaprete said: "We need to look a bit closer before we conclude anything about an ejecta cloud or not ... Life is full of surprises and we don't want to make a false positive or false negative claim. I'm excited that we saw variations in the spectra.
"We're going to be working on this feverishly. We've just not been able to see [the plume] clearly in our image data yet, but we're going to go back and look more closely," Dr Colaprete said. Finding water in the Cabeus crater would have immense implications for space exploration. Not only would it provide a source of drinking water for a permanently manned lunar base, but also a source of hydrogen for making rocket fuel to visit Mars and beyond.
"A means to produce rocket fuel on the Moon could make a more ambitious space exploration programme feasible at lower cost. While the Moon's surface is full of oxygen in mineral forms, hydrogen is the other key element that could make rocket fuel production practical on the Moon," Nasa said.
More than a dozen professional telescopes monitored the impact from Earth, which was also analysed by a handful of space telescopes, including the Hubble. They could add further critical data on the detection or otherwise of the hydroxyl molecule, to confirm the presence of frozen water in shaded craters where temperatures never rise above about -210C.
Nasa estimates that there are 12,500sqkm of permanently shadowed terrain on the Moon and if the top metre of this area were to hold one per cent by mass of water, this would still produce thousands of litres of water.
It is not the first time that a spacecraft has crashed into the Moon. In 1998, Nasa's Lunar Prospector mission was deliberately crashed into a crater, confirming the presence of hydrogen.