A speculation for decades that the moon’s thin atmosphere contains neon, which is known for use in electric signs on Earth with its typical characteristsics of intense glow has come true finally with NASA’s Lunar Atmosphere and Dust Environment Explorer (LADEE) spacecraft confirming the existence of the gas for the first time.
The speculation has been there since the Apollo missions in the late 1960s and early 70s, 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.”
In her paper on LADEE’s Neutral Mass Spectrometer (NMS) instrument’s findings that was published May 28 in Geophysical Research Letters, she said, “It’s critical to learn about the lunar exosphere before sustained human exploration substantially alters it.”
Since the moon’s atmosphere is tenuous and thin, rocket exhaust and outgassing from spacecraft could easily change its composition and this could be the reason why not enough neon was deciphered earlier on the moon. The tenous atmposphere on moon is about 100 trillion times less dense than Earth. A dense atmosphere like Earth’s is relatively rare in our solar system as any object has to be massive to have enough gravity to hold onto it.
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.
Most of the moon’s exosphere comes from the solar wind, which is hydrogen and helium, but it contains many other elements in small amounts, including neon. All these elements impact the moon, but only helium, neon, and argon are volatile enough to be returned back to space. The rest of the elements will stick indefinitely to the moon’s surface.
The LADEE NMS instrument confirms that the moon’s exosphere is made up of mostly helium, argon, and neon. Their relative abundance is linked to the time of day on the moon–argon peaks at sunrise, with neon at 4 a.m. and helium at 1 a.m. The LADEE NMS instrument measured these gases for seven months to arrive at these findings.
“These discoveries highlight the limitations of current exospheric models, and the need for more sophisticated ones in the future,” said Benna.
LADEE was launched in September 2013 and began orbiting the moon from Oct. 6 the same year collecting data from Nov. 10. The spacecraft entered its science orbit around the moon’s equator on Nov. 20, and in March 2014, LADEE extended its mission operations into the lunar surface, impacting the moon on April 17, 2014. The spacecraft’s orbit naturally decayed following the mission’s final low-altitude science phase due to lack of fuel.