A team of researchers has discovered the first evidence of water on the moon. A new type of chemical analysis has spotted the telltale signs of water molecules inside tiny beads of volcanic glass brought to Earth decades ago by the Apollo astronauts. The find may force astronomers to rethink their theories of how the moon formed, and it might mean that future missions could mine water from the lunar soil, helping to sustain colonists and fuel voyages to other planets.
Soon after it coalesced, about 4.5 billion years ago, Earth took at hit from a Mars-sized object. The resulting cloud of debris eventually condensed to form the moon--or so the current thinking goes. But if the moon came from Earth, and Earth is awash with water, where is the lunar water?
Many planetary scientists think any water blown away from Earth by the impact would have been instantly vaporized by the high temperatures of the collision. Nevertheless, some researchers continue to believe that the moon does contain some water, perhaps locked deep within its interior. Over the years, they've intensely scanned tiny glass beads--brought back by the Apollo missions in the 1960s and 1970s--that had been ejected from inside the moon by volcanic eruptions about 3 billion years ago. Up to now, however, these samples have shown no evidence that the liquid ever existed on the moon.
A team led by geochemist Alberto Saal of Brown University decided to use a more sensitive method. The technique, called secondary ion mass spectrometry, was developed to detect trace amounts of volatile gases such as chlorine and fluorine in Earth soil samples. Applying it to the lunar samples, the team found trace amounts of water--about 46 parts per million--in the volcanic beads. Because the water was embedded in the beads, it can't be a contaminant picked up since the samples arrived on Earth, the researchers report tomorrow in Nature.
Saal declines to speculate about how much water the moon contains or if any of it is still present in liquid form. Extrapolating the results to estimate the amount of lunar water would be like predicting "the final score of the game after we saw the first touchdown in the first 5 minutes of the first quarter," he says. Meanwhile, he and his team will be studying as many lunar glass beads as possible to refine their analysis.
Planetary scientist David Stevenson of the California Institute of Technology in Pasadena calls the findings important and says they open up a new possibility. "It is likely that at the time of the giant impact, Earth had water and the impacting body had water," he says, so some of that water might still be trapped in the moon.
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