When astronauts from the Apollo 17 mission landed on the Moon in 1972, one of their mission objectives was to analyze the tenuous atmosphere using the Lunar Atmosphere Composition Experiment, a mass spectrometer (with a shape and appearance weirdly reminiscent of a modern day printer/scanner combo) designed to detect traces of gas in the lunar firmament.
At the time, readings from LACE had suggested that helium was present in the lunar atmosphere. Now, forty years later, readings from NASA's Lunar Reconnaissance Orbiter have corroborated LACE's findings — and the confirmation raises some interesting questions. For instance, does the helium originate from inside the Moon, or from an external source like solar wind? How do helium concentrations vary with altitude? And why do atmospheric helium levels tend to drop as night sets in?
LRO's assessment is also a testament to its versatility as a scientific instrument. Even though the orbiter is primarily a surface-mapping tool, NASA hopes it can provide some answers to questions surrounding the Moon's helium-rich atmosphere on the side. "These ground-breaking measurements were enabled by our flexible operations of LRO as a science mission," explained LRO project scientist Richard Vondrak in a statement, "so that we can now understand the moon in ways that were not expected when LRO was launched in 2009."
Read more about LRO and the Moon's mysterious, helium-rich atmosphere over at MSNBC.