NASA scientists confirmed that the bright luminescence seen surrounding the exosphere of the moon over the decades is in fact neon, a type of gas that often used to give electric signs on Earth their intense and alluring glow.
The confirmation was made through the help of instruments on board the American space agency's spacecraft known as the Lunar Atmosphere and Dust Environment Explorer (LADEE).
Space expert Mehdi Benna, at the Goddard Space Flight Center of NASA, explained that while the presence of the gas neon in the moon's exosphere has long been debated on since the Apollo space missions, there has been no reliable detections made over the years.
Benna, who led a team of researchers in studying the LADEE observations, added that they were not only able to confirm the existence of neon, but that the gas is relatively abundant in the exosphere of the moon.
NASA said that the moon does not have enough neon to make it glow more visibly because its exosphere is 100 trillion times less dense compared to the atmosphere of the Earth at sea level. The density of the Earth's own atmosphere makes it relatively uncommon in the solar system because for gravity to be able to effectively hold on to an object, it has to be massive in size.
The Neutral Mass Spectrometer (NMS) featured in the LADEE spacecraft verified that the exosphere of the moon consists of mostly of neon, argon and helium. The abundance of these gases is dependent on the moon's time of day.
NASA instruments show that argon is most abundant on the moon during sunrise, neon is mostly detected at 4 a.m. and helium is at 1 a.m.
The NMS carried out systematic measurements of the gases in the moon's exosphere for a seven-month period, allowing NASA scientists to find out how these gases are released to the lunar atmosphere, as well as how they are eventually lost.
A majority of the exosphere is known to be supplied by solar wind, but data collected from the NMS showed that some of the gases found in the moon's atmosphere originate from lunar rocks. The element Argon-40 is derived from decaying potassium-40 that can be found in terrestrial planet rocks as a leftover from its development.
Benna said that they also discovered that argon-40 causes the creation of a local bulge high above an odd part of the surface of the moon, which contains Oceanus Procellarum and Mare Imbrium. The cause of this occurrence, however, is not yet clearly understood.
"One could not help to notice that this region happens to be the place where potassium-40 is most abundant on the surface," Benna said.
"So there may be a connection between the atmospheric argon, the surface potassium and deep interior sources."
The findings of the NASA Goddard Space Flight Center study are featured in the journal Geophysical Research Letters.
