Evidence of moon water found

Using a technique that was not available when Apollo astronauts collected the minuscule rocks in the early 1970s, scientists were able to detect telltale signs of water trapped inside the pebble-like glass. Their discovery suggests that water was present deep within the moon when the pebbles were formed during violent lunar eruptions 3.3 billion to 3.6 billion years ago.

The analysis, published today in the journal Nature, may cause scientists to rethink theories on how the moon was formed.

"The water that these guys have discovered is a scientific gold mine for us to figure out the history of . . . the moon," said Jim Garvin, chief scientist at NASA's Goddard Space Flight Center, who was not involved in the research.

The pebbles, about the size of a period on this page, are made of magnesium-rich green volcanic glass and iron-rich orange glass that solidified moments after eruption. They were recovered from the moon's equatorial region during the Apollo 15 and Apollo 17 space missions.

Earlier studies of the pebbles detected the presence of sulfur and carbon, indicating the volcanic glass was formed in a fiery eruption.

For the latest study, scientists measured the composition of the diminutive rocks molecule by molecule, using a technique 10 times more sensitive than that used in previous work.

They didn't search for water directly because when water is incorporated into any rock it naturally separates into smaller components. So researchers looked for one of those components, hydrogen, which would signal the presence of water.

Testing the interior of the pebbles to avoid surface contamination, scientists found trace amounts of hydrogen along with chlorine and fluorine, which, like carbon and sulfur, are found in rocks from explosive eruptions. The discovery of hydrogen alongside the other elements suggested to scientists that the water came from inside the moon and not from an external source, such as a comet.

Based on the amount of hydrogen found in the pebbles, scientists estimated the lunar magma contained 260 to 745 parts per million of water, similar to what is found in the Earth's upper mantle.