Space.com is reporting that the Lunar Reconnaissance Orbiter has confirmed the presence of helium in the lunar atmosphere, something that was indicated by an experiment conducted by the Apollo 17 astronauts and suspected by scientists.
It is a popular misconception that the moon lacks an atmosphere. That is not entirely true. According to Moon Zoo, the moon has a very tenuous atmosphere that contains sodium, potassium, radon, polonium, argon, helium, nitrogen, oxygen, methane, carbon dioxide and carbon monoxide. The density of the lunar atmosphere is so tenuous that it contains about 80,000 atoms per cubic centimeters, which would qualify as vacuum in certain laboratory experiments. Scientists suggest that because most atoms are able to escape the low gravity from the moon, the lunar atmosphere is renewed in some manner, likely a combination of solar wind, comet and meteor impacts, and outgasing from the lunar interior.
Helium and Apollo 17
According to NASA's Jet Propulsion laboratory, the Apollo 17 astronauts deployed an experiment called Lunar Atmospheric Composition Experiment (LACE) on the lunar surface. LACE consisted of a mass spectrometer that measured the composition of the lunar atmosphere. LACE found helium, neon, and hydrogen in roughly equal amounts. A smaller number of other gasses were found as well.
LRO's Lyman Alpha Mapping Project detected helium
According to NASA's Lunar Reconnaissance Orbiter page, the instrument on the LRO that picked up hydrogen was the Lyman-Alpha Mapping Project (LAMP). LAMP was an ultraviolet instrument that was used to help detect the existence of water ice within the permanently shadowed craters at the lunar poles. According to the Space.com account, LAMP was retasked to confirm the existence of helium in the lunar atmosphere in a campaign taking 50 polar orbits of the moon. Some care was take to make sure that the helium being detected was not just floating in interplanetary space but was in fact part of the lunar atmosphere.
Where the helium comes from
LAMP will now be used to determine where the source of the helium is, according to the Space.com account. Scientists are divided over where the helium is coming from. Some suggest that the helium in the lunar atmosphere is the result of outgassing from the lunar interior, as a result of the radioactive decay of rocks. Others maintain that the helium is being deposited from the outside, by solar wind or the impact of comets and meteors.
Mark R. Whittington is the author of Children of Apollo and The Last Moonwalker. He has written on space subjects for a variety of periodicals, including The Houston Chronicle, The Washington Post, USA Today, the L.A. Times, and The Weekly Standard.