The LAMP spectrometer installed on board the Lunar Reconnaissance Orbiter station allowed scientists to study the range of substances contained in the atmosphere of the Moon. In particular, it was found that the lunar atmosphere contained helium and argon. The first analyses of the spectrum were made in 1972 as part of the LACE project that was executed by Apollo 17 mission.

Forty years ago, Apollo equipment determined that the amount of lunar helium grows at nighttime. Perhaps this is because the colder atmosphere in the dark time of the lunar day increases the concentration of atoms of this gas at low altitudes.

Although the main objective of LAMP is to display the lunar surface, researchers decided to explore the remote ultraviolet radiation above the Earth's satellite. The presence of helium in the lunar atmosphere was finally confirmed after Apollo orbited the Moon more than fifty times. The equipment managed to suppress the background interplanetary noise (helium may also be present in outer space).

http://english.pravda.ru/science/tech/31-08-2012/122040-moon_atmosp...