Artist’s concept
of NASA's Lunar Atmosphere and Dust Environment Explorer (LADEE) spacecraft in
orbit
above the moon. Credits: NASA Ames / Dana Berry
(August 18, 2015) The
moon's thin atmosphere contains neon, a gas commonly used in electric signs on
Earth because of its intense glow. While scientists have speculated on the
presence of neon in the lunar atmosphere for decades, NASA's Lunar Atmosphere
and Dust Environment Explorer (LADEE) spacecraft has confirmed its existence
for the first time.
"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, Maryland and the University of Maryland, Baltimore County.
"We were very pleased to not only finally confirm its presence, but to
show that it is relatively abundant." Benna is lead author of a paper
describing observations from LADEE's Neutral Mass Spectrometer (NMS) instrument
published May 28 in Geophysical Research Letters.
There's not enough neon to make the moon visibly glow
because the moon's atmosphere is extremely tenuous, about 100 trillion times
less dense than Earth's atmosphere at sea level. A dense atmosphere like
Earth's is relatively rare in our solar system because an object has to be
sufficiently massive to have enough gravity to hold onto it.
The behavior of a dense atmosphere is driven by collisions
between its atoms and molecules. However, the moon's atmosphere is technically
referred to as an exosphere because it’s so thin, its atoms rarely collide.
Exospheres are the most common type of atmosphere in our solar system, so
scientists are interested in learning more about them. "It's critical to
learn about the lunar exosphere before sustained human exploration
substantially alters it," Benna said. Since the moon's atmosphere is so
thin, rocket exhaust and outgassing from spacecraft could easily change its
composition.