Finding Water on the Moon

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Lunar particles: These lunar volcanic glasses were analyzed using NanoSIMS to show the presence of water in the interior of the moon. The green glass beads were collected from the Apollo 15 landing site at Hadley Rille on the moon. They represent volcanic deposits formed early in the moon’s geological history. Credit: NASA

To enable the technology to detect such a small amount of hydrogen, Hauri first improved the vacuum of the instrument. Any free gas gets deposited on the sample surface, contaminating it. Prior generations of the instrument have, on average, detection limits around 100 parts per million, but with a better vacuum the scientists were able to achieve a detection limit of five parts per million.

Hauri's technique also included using a different high-energy primary ion beam. Most SIMS instruments use a beam of oxygen ions and collect positively charged ions. Instead, Hauri used a cesium beam to measure negatively charged hydroxyl ions that are ejected from the sample. The cesium ion beam is a much more sensitive method of analyzing water, says Hauri.

NanoSIMS has also allowed scientists to, for the first time, simultaneously measure several elements in the samples instead of just one, says Claude Lechene, a professor at Harvard Medical School and the director of the National Resource for Imaging Mass Spectrometry, in Cambridge, MA. In previous technology, if scientists wanted to analyze more than one element, they would have had to adjust the magnetic field. "The new system can measure five or seven masses concurrently," says Stadermann, making the analysis much more efficient.

Stadermann says that the new work is an excellent use of the NanoSIMS technology. "This is one of the many steps of the broader uses of NanoSIMS," says Stadermann. "I fully anticipate that there will be many more discoveries being made using the technology. You have capabilities that you did not have with instruments before."