The Moon has long been thought to be highly depleted in volatiles such as water. Direct measurements of water in lunar volcanic glasses have never exceeded 50 parts per million (ppm). These low quantities have been used as evidence that the Moon was formed as a result of a collision that generated high temperatures.

Erik Hauri and co-workers, Carnegie Institution of Washington, USA, have measured the water content of lunar melt inclusions with an ion microprobe. Lunar melt inclusions are particles of molten rock trapped within crystals in volcanic glass. The encasing in the crystals prevents escape of water and other volatiles during volcanic eruption and gives a clearer indication of pre-eruption concentrations.

The team was able to show that that some parts of the lunar interior contain as much water as Earth’s upper mantle. Water levels of 615 to 1410 ppm were detected along with higher amounts of fluorine, sulfur and chlorine than anticipated.

This could force the prevailing theory of the Moon’s origin to be re-examined.

• High Pre-Eruptive Water Contents Preserved in Lunar Melt Inclusions
  E. H. Hauri, T. Weinreich, A. E. Saal, M. C. Rutherford, J. A. Van Orman,
  Science 2011.
  DOI: 10.1126/science.1204626