A new scan has shown the presence of water in Moon rock at levels not previously thought possible.
A team from the Carnegie Institution for Science in Washington developed a new form of materials analysis called secondary ion mass spectrometry.
The technique was tested on samples of Moon rock brought back from the Apollo landings in the 1960s and 1970s.
When the samples were scanned they were found to contain hydrogen, similar to that found in the Earth's mantle.
"We looked at many factors over a wide range of cooling rates that would affect all the volatiles simultaneously and came up with the right mix," said James Van Orman, a former Carnegie researcher now at Case Western Reserve University.
"It suggests the intriguing possibility that the Moon's interior might have had as much water as the Earth's upper mantle."
Scientists believe that the Moon was formed by an object the size of Mars crashing into the Earth and knocking debris into orbit.
The process of lunar formation would have been intensely hot and this, coupled with the lack of atmosphere, would have led to any water boiling away.
Scientists have suggested that some water from comets may be found in rock formations at the Moon's poles but the idea of naturally occurring water had been largely discounted.
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