There's helium in the moon's atmosphere, and we don't quite know why.

Wait, the moon has an atmosphere, you ask? You thought it was a vacuum, right? Why, yes it does have an atmosphere - technically speaking. But for all practical purposes such as landing and habitation - no. In fact, the lunar atmosphere is so tenuous that it is really more properly known as an "exosphere", and it can only be measured with sensitive scientific instruments.

To illustrate how tenuous the lunar exosphere is, it's reported that the weight of a feather dropped on your hand would exert 1 trillion times more pressure than the lunar atmosphere. David Woods, in a recent podcast, mentioned that the total lunar atmosphere is about 10 tons. That's about the same amount as the weight of the propellant used during the lunar activities in each Apollo mission. So, essentially, each Apollo mission doubled the total weight of the lunar atmosphere (though these extra molecules very quickly dissipated due to the solar wind).

But back to helium. We knew from instruments deployed by the Apollo missions that the moon has a tiny atmosphere, composed mostly of argon and helium, with trace amounts of sodium, potassium, and hydrogen. NASA's Lunar Reconnaissance Orbiter has recently confirmed the presence of helium in the lunar atmosphere. What's new in this announcement is that the helium concentrations fluctuate, and that in turn highlights the fact that we don't know where that helium comes from. Is it outgassing from lunar minerals? 

Alan Stern of the Southwest Research Institute in Boulder, Colo., said in a statement

The question now becomes, does the helium originate from inside the moon — for example, due to radioactive decay in rocks — or from an exterior source, such as the solar wind? If we find the solar wind is responsible, that will teach us a lot about how the same process works in other airless bodies.

More info on the LRO finding after the jump. And check out David Wood's book "How Apollo Flew to the Moon" - essential reading for those interested in the Apollo missions and one of the best books ever written on the subject. The above-mentioned Omega Tau podcast(s) with Mr. Woods is similarly outstanding and highly recommended.

Image courtesy: NASA

 

NASA orbiter confirms there's helium in moon's atmosphere

MSNBC, 16 August 2012

A NASA spacecraft has detected helium in the moon's tenuous atmosphere, confirming observations made four decades ago on the lunar surface.

NASA's Lunar Reconnaissance Orbiter (LRO) sniffed out the helium from above with an onboard spectrometer. The finding corroborates measurements made by the Lunar Atmosphere Composition Experiment (LACE), which was deployed by moonwalking Apollo 17 astronauts in 1972.

"The question now becomes, does the helium originate from inside the moon — for example, due to radioactive decay in rocks — or from an exterior source, such as the solar wind?" Alan Stern of the Southwest Research Institute in Boulder, Colo., said in a statement. Stern is principal investigator of LRO's Lyman Alpha Mapping Project spectrometer, or LAMP.

NASA

The Lunar Atmosphere Composition Experiment (LACE), deployed by Apollo 17 astronauts in 1972, provided the first measurements of helium in the moon's atmosphere.

While LAMP is primarily a surface-mapping tool, researchers used the instrument to study the moon's thin atmosphere over a campaign lasting more than 50 orbits. They detected helium, then applied several different techniques to confirm that LAMP wasn't just picking up gas in the interplanetary background. [ 10 Coolest Moon Discoveries by LRO ]

Further LAMP observations could help scientists nail down the dominant source of the helium, Stern said.

"If we find the solar wind is responsible, that will teach us a lot about how the same process works in other airless bodies," Stern said.

The LACE measurements from the 1970s showed an increase in helium abundance as night progressed, a result that could be explained by atmospheric cooling (which concentrates atoms at lower altitudes). LAMP should build on those findings by investigating how helium abundances vary with latitude, researchers said.

The $504 million LRO probe launched in June 2009 along with a piggyback spacecraft called LCROSS. In October of that year, LCROSS slammed intentionally into a shadowed crater at the moon's south pole, unearthing lots of water ice.

LRO is about the size of a Mini Cooper, and it carries seven instruments to observe the moon. The spacecraft circles the moon in a polar orbit, at an altitude of about 31 miles (50 kilometers).

For the first year of its operational life, LRO scouted the moon to help NASA plan for future lunar exploration missions. In September 2010, the probe wrapped up this mission and shifted into a pure science mode.

"These ground-breaking measurements were enabled by our flexible operations of LRO as a science mission, so that we can now understand the moon in ways that were not expected when LRO was launched in 2009," said Richard Vondrak, LRO project scientist at NASA’s Goddard Space Flight Center in Greenbelt, Md.

via www.msnbc.msn.com