Finding Water on the Moon

An advanced type of mass spectrometry has detected water in lunar particles.

Last week's announcement of the discovery of evidence of water in lunar volcanic glass beads brought back from the moon during the Apollo missions in 1971--a finding that is causing scientists to rethink the conventional theory of the moon's formation--was made possible by recent advances in an analytical technique called nano secondary ion mass spectroscopy or NanoSIMS.

Analyzing tiny samples: The French company CAMECA has made an instrument called the nano secondary ion mass spectrometer (NanoSIMS) that is being used by scientists to analyze small particles, such as the lunar volcanic glass beads from the Apollo missions. Using the instrument, scientists were able to discover evidence of water in the lunar samples. This particular instrument is located in the Laboratory for Space Sciences at Washington University, in St. Louis. Credit: Frank Stadermann, Washington University

NanoSIMS, which was developed by the French company CAMECA, is a variation of an established technique called secondary ion mass spectroscopy (SIMS), but it has a higher spatial resolution and can measure a handful of elements simultaneously, says Frank Stadermann, a senior research scientist at the Laboratory for Space Sciences at Washington University, in St. Louis.

With SIMS, a high-energy ion beam is focused on the surface of a sample. The impact of the beam causes atoms to be ejected from the surface; some of the atoms get ionized and then pass through a mass spectrometer that determines the composition of the sample material. The NanoSIMS instrument has an ion beam that can focus down to a diameter of less than one micrometer, whereas previous SIMS technology could only focus down to around 20 micrometers.

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While researchers have been using NanoSIMS to study the isotopic composition of small particles, such as planetary dust and volcanic glasses, this is the first time that the technique has been able to detect traces of hydrogen. "The key part was, we developed a method for measuring very low water content on other SIMS instruments and applied the same methodology on the NanoSIMS," says Erik Hauri, a staff scientist with the Carnegie Institution for Science, in Washington, DC, and one of several authors of the study last week describing evidence of water in lunar samples. "This allowed us to take measurements on a very small spatial scale. The limit for detecting water was about 50 parts per million at best. We developed a way to detect as little as five parts per million of water, and surprisingly, we found up to 46 parts per million in these tiny glass beads."

The study was published on July 10 in the journal Nature and conducted by scientists from Brown University, Carnegie Institution for Science, and Case Western Reserve University.