There are large quantities of frozen water in some regions of the moon, according to a study of debris kicked up by a rocket that crashed into its surface last year.
Last autumn, Nasa scientists steered the upper stage of an Atlas V rocket travelling at 5,600 miles per hour into a deep crater as part of the US space agency's hunt for signs of water on the moon. The impact was recorded by a spacecraft flying behind the rocket, called the Lunar Crater Observation and Sensing Satellite (LCROSS), and by cameras on Nasa's Lunar Reconnaissance Orbiter as it circled the moon.
In a series of papers published in the journal Science, Nasa researchers describe how the crash punched a crater in the moon between 25m and 30m wide and created a plume of debris more than half a mile high. Sensors aboard LCROSS detected about 155kg of ice in a single "snapshot" following the impact. In one of the papers, a team led by Anthony Colaprete at Nasa's Ames Research Centre in California estimated that frozen water accounted for about 5.6% of the material in the crater.
"What we found was, I would say, an oasis in an otherwise desert on the moon that has highly concentrated water with respect to the moon, and a lot of other materials," Colaprete said.
Instruments aboard LCROSS spotted a range of chemicals in the debris plume, including alcohol, methane, ammonia and silver. For every 100g of ice, the spacecraft sniffed about 1.55g of alcohol.
The spent rocket ploughed into a 60-mile-wide crater called Cabeus that sits in permanent shade at the lunar south pole. The floor of the crater is thought to be one of the coldest places on the moon.
In a companion study, a group led by Paul Hayne at the University of California, Los Angeles, used heat sensors on the Lunar Reconnaissance Orbiter to analyse the crash from space. When the rocket struck, it produced enough heat to warm an area on the surface of between 30 and 200 square metres, from about -233C to 677C. The researchers say the heat was enough to release 300kg of water ice in the four minutes that followed the crash.
Finding useful quantities of frozen water on the moon would have implications for space exploration. Not only would it provide water and oxygen for a manned moonbase, it would also give astronauts a source of hydrogen to use in rocket fuel. Extracting gases from water becomes cost-effective when the amount of ice in lunar soil rises above 1%, Colaprete said. At the levels found, astronauts could extract more than 100 litres of water from every cubic metre, said Ian Crawford, a planetary scientist at Birkbeck College, London.
"If you have this amount of water in the lunar regolith [a layer of loose material covering solid rock] down to a few metres then it starts to become useful. Even if it's at the bottom of a crater, it's easier to extract oxygen and hydrogen from water than it is from rocks on the surface."
This article was amended on 22nd October 2010. The original stated that a cubic metre of lunar soil would yield 100 millilitres of water. This has been corrected.