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Hopes dashed for ice at Moon's south pole

Moon's south pole

This image of the lunar south pole, together with radar echoes, was thought to be evidence for ice. Now scientists say it isn't ice, just rough terrain (Image: Clementine, BMDO, NRL, LLNL)

Hopes that the Moon's south pole has a vast hoard of ice that could be used to establish a lunar colony are sadly unfounded, a new study says.

In 1994, radar echoes sent back in an experiment involving a US orbiter called Clementine appeared to show a treasure trove of frozen water below craters near the lunar south pole.

At the time, scientists saw this as evidence of ice in areas that were permanently shaded from the Sun.

If so, such a find would be an invaluable boost to colonisation, as the ice could be used to provide water as well as hydrogen as fuel.

NASA is looking closely at the south pole as a potential site for the US return mission to the Moon, scheduled to take place by 2020.

But a paper published today in the journal Nature says the Clementine data was most probably misinterpreted.

Professor Donald Campbell of Cornell University and colleagues, including Dr Nicholas Stacy from Australia's Defence Science and Technology Organisation, collected radar images of the Moon's south pole to a resolution of 20 metres.

They looked especially at Shackleton crater, which had generated most interest.

The team found that a particular radar signature called the circular polarisation ratio, which in the Clementine experiment was taken to indicate thick deposits of ice, could also be created by echoes from the rough terrain and walls of impact craters.

The signature was found in both sunny and permanently shady areas of crater, which suggests that the reflection comes from rocky debris, not thick ice deposits.

If there is any ice at the south pole, it probably comes from tiny, scattered grains that probably account for only 1-2% of the local dust, the authors suggest.

"Any planning for future exploitation of hydrogen at the Moon's south pole should be constrained by this low average abundance rather than by the expectation of localised deposits at higher concentrations," the paper says.

The research involved sending a radar signal from the Arecibo telescope in Puerto Rico.

The signal hit the southern lunar region and the reflection was picked up by the US Green Bank Telescope.

Tags: astronomy-space