Finally, we have proof of the moon’s “noble” heritage! Measurements from NASA’s Lunar Atmosphere and Dust Environment Explorer, aka LADEE (pronounced “laddie”) have confirmed the long-suspected presence of neon in its atmosphere (neon is one of the noble gases — see what I did there?) along with isotopes of argon and helium. The relative concentrations of each of these elements also appears to depend on the time of day.
“The presence of neon in the exosphere of the moon has been a subject of speculation since the Apollo missions, but no credible detections were made,” said Mehdi Benna of NASA’s Goddard Space Flight Center in Greenbelt, Md., and the University of Maryland, Baltimore County, lead author of a paper describing the findings. “We were very pleased to not only finally confirm its presence, but to show that it is relatively abundant.”
Of course, this has nothing to do with the appearance of the moon from Earth. Despite its “relative abundance” the amount of neon in the lunar atmosphere is much too sparse to actually create any visible glow.
These elements in the lunar atmosphere have their source in the solar wind. As this constant stream of charged particles from the sun encounters the moon, heavier elements remain on the surface while lighter and more volatile elements like neon and argon return to space… except for the small portion that get trapped by gravity.
While we say “atmosphere,” in realty what the moon has is an exosphere — an extremely diffuse cloud of atoms, ions, and fine dust particles held in place by the moon’s weak gravity. It’s nothing a human could breathe or even feel; it’s 100 trillion times less dense than air on Earth at sea level.
Still, it’s something that interacts with the solar wind environment and, possibly, whatever activities we may one day establish on the lunar surface. Such a thin and fragile exosphere could easily be disturbed by rocket exhaust or outgassing from a permanent base, for example.
“It’s critical to learn about the lunar exosphere before sustained human exploration substantially alters it,” said Benna.
The presence of the moon’s exosphere was famously hinted at in a series of sketches made by Apollo 17 astronaut Gene Cernan, who claimed to have witnessed a lunar horizon glow (referred to as LHG in true NASA form) as well as long “streamers” of light preceding a sunrise from lunar orbit. While LADEE could not observe this phenomenon with its star tracker cameras, its Neutral Mass Spectrometer did collect the numbers.
Launched from NASA’s Wallops Flight Facility in Virginia on Sept. 6, 2013, the 844-lb (383-kg) NASA Ames-built LADEE arrived in lunar orbit 30 days later and, after a month reviewing the functionality of its instruments, began its 100-day-long scientific investigation of the Moon’s atmosphere. LADEE’s mission came to an end when it impacted the surface of the moon as planned on the evening of April 17, 2014.
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