(Sen) - NASA’s Lunar Reconnaissance Orbiter (LRO) has made the first spectroscopic observation of helium in the tenuous atmosphere of the Moon.
The measurements were made with the Lyman Alpha Mapping Project (LAMP) aboard LRO. The appropriately named LAMP is used to peer into shadowed areas of the Moon by utilising the soft glow of ultraviolet light from nearby stars.
LAMP was designed to map the surface of the Moon, but scientists have been able to push the boundaries by using the instrument to observe the tenuous lunar atmosphere in the ultraviolet region. Helium signatures from the interplanetary background had to be removed from the data before helium could be confirmed in existence around the Moon.
"The question now becomes, does the helium originate from inside the moon, for example, due to radioactive decay in rocks, or from an exterior source, such as the solar wind?" asks LAMP principal investigator Alan Stern. "If we find the solar wind is responsible, that will teach us a lot about how the same process works in other airless bodies."
If there is no correlation between the solar wind and the helium in the Moon's atmosphere, then it is possible that the helium is being produced in the interior. Helium could be released during lunar quakes, or it could be the result of radioactive decay.
"With LAMP's global views as it moves across the Moon in future observations, we'll be in a great position to better determine the dominant source of the helium," says Stern. LAMP will also seek other gases, such as argon, on future orbits.
Helium has previously been detected on the Moon with the Lunar Atmosphere Composition Experiment (LACE) which was deployed by Apollo 17 astronauts in 1972. LACE noted an increase in helium as night fell on the Moon, meaning its presence could be due to atmospheric cooling, which would cause the helium to concentrate at low latitudes. LAMP will investigate this further by measuring the helium at different latitudes.
"These ground-breaking measurements were enabled by our flexible operations of LRO as a Science Mission, so that we can now understand the Moon in ways that were not expected when LRO was launched in 2009," says Richard Vondrak, LRO project scientist.
The Lunar Reconnaissance Orbiter was launched in 2009 and resides in a polar orbit 50 kilometres above the Moon’s surface. The satellite’s mission is to create a 3D map of the Moon, which will assist in selecting landing sites for future missions.