In its most violent mission so far, the US space agency Nasa slammed two probes into the moon, in the hope of detecting lunar ice in a plume of moondust.
But the event was an anticlimax for many thousands of people around the world watching live images on the internet as a two-tonne Centaur rocket hit the target. There was no sign of the expected flash or explosion and no obvious dust cloud rising from the impact zone, the Cabeus crater near the lunar south pole.
The LCross (Lunar Crater Observation and Sensing Satellite) craft, which was taking the pictures, itself slammed into the lunar surface as planned, four minutes later.
Nasa officials insisted afterwards that the $79m mission had been a success. They said instruments on LCross, other spacecraft and terrestrial telescopes focused on the moon would analyse the impacts to determine whether ice does indeed lie in the permanently shaded rim of Cabeus.
The identification of water in the impact debris would be an important scientific discovery – and could be a valuable resource for any future human base on the moon.
“The LCross science instruments worked exceedingly well and returned a wealth of data that will greatly improve our understanding of our closest celestial neighbour,” said Anthony Colaprete, project scientist at Nasa’s Ames Research Centre. “The team is excited to dive into the data.”
Before the dual impacts, scientists had speculated about a possible dust plume 10km high that might be visible by amateur astronomers. In the event, even giant telescopes saw no obvious plume – or “ejecta” in Nasa-speak – perhaps because the lunar surface was harder than predicted, perhaps because the angle of approach or the lighting conditions were unfavourable.
“Luck has to come in to get the ejecta to fly in the way we want it to fly,” Mr Colaprete told a post-impact news conference. “But I’m not convinced that we will not see the ejecta when we look more closely [at the images].”
What LCross and some other telescopes did record was a thermal “hot spot” where the Centaur rocket hit and the faint image of a new crater about 20 metres wide made by the impact.
Most importantly, the Nasa team have measurements from spectrometers – scientific instruments that show the chemical signature of the impact.
But Mr Colaprete said it might be days, weeks or even months before the team was ready to say how much water had been detected, if any.
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