LADEE and Jumping Lunar Dust - MyMoon

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LADEE AND JUMPING LUNAR DUST

Part of the goal for LADEE is to study the lunar atmosphere. In fact, it’s right in the spacecraft’s name: Lunar Atmosphere and Dust Environment Explorer.

“But hold up”, you might say, “doesn’t the Moon not have its own atmosphere? Last I knew, there was no air on the Moon.” And you’d be right. Well, almost.

The simple story is that the Moon isn’t massive enough to hold on to an atmosphere. The Earth can have an atmosphere because its gravity is strong enough to hold onto the particles in its atmosphere. Since the Moon is less massive, its gravitational attraction to particles is lower, and therefore a slower escape velocity is necessary to escape from the Moon’s bounds. Therefore, the Moon will start to lose its atmosphere over time.

However, the key is that this is true over the long term. Particles in the lunar atmosphere, on average, don’t always have a high enough velocity to escape from the Moon. Over time, they can gain higher velocities through higher temperatures (thermal excitations) or hitting one another (collisions). Once they do, their velocity can exceed the escape velocity. Since this is lower for the Moon than other places like the Earth, it can happen more frequently and the Moon tends to lose most of the particles in its atmosphere. But this still leaves room for some particles in the lunar atmosphere, especially newer ones. So the Moon can, in fact, have a small atmosphere, made up almost entirely of new particles. And this is where the story for LADEE gets really interesting.

Most of the particles in the lunar atmosphere are thought to be dust from the Moon’s surface. Some theories suggest that radiation from the Sun could excite electrons on the lunar surface and cause them to be expelled. Over time, this would make the surface of the Moon more positively charged, which would cause some of the lightest particles of dust on the surface to be launched up! (It does sound a little far-fetched; in fact it was first predicted in science fiction by Hal Clement in 1956.) This would end up continually contributing to the lunar atmosphere.

inline image Lunar dust jumping from the surface, from Stubbs et al. (2005).

LADEE’s instruments are designed to study this atmosphere. They can perform spectrometry on the dust and even collect samples of the dust to help examine its makeup. With these instruments, LADEE can help us understand how the Moon has built up an atmosphere, as small as it is.

COMMUNITY COMMENTS:

Nick A.

Monday Sep-23-2013

Great blog---excited to see the crazy findings LADEE might uncover with all the weirdness going on with the Moon's surface (and it's jumping particles).

I love the "Dust follows ballistic trajectory"

Dennis M J M.

Thursday Sep-26-2013

nice ref^ to "Dust Rag", its amazing how much truth lay in the early visions of space, based largely on inference with basically NO facts... I haev a great book of space art from the early days and their imaginings of the surfaces of distant moons and stuff isn't far off we now know. some of the things they were wrong about are pretty funny too. I note that no one ever predicted the software we think of today as 'social media' until myspace, basically. I mean they were flying at light speed using computers to hyperjump for years... but still communicated on walkie talkies into the 2300s in some interpretations ?

I guess you never know. Thank goodness those gawd-awful robots from LOST IN SPACE aren't likely to appear thanks to Boston Dynamics ;) unless they turn out to be the 'dollar store' type, you know...always going off "DANGER DANGER!!" when no ones around. :P

Abhimat G.

Monday Sep-30-2013

What I sort of also find really neat about looking back at old science fiction is that at first you might think that it kind of sucks that it’s already 2013 and we don‘t have some of the awesome things they predict we should have, like flying cars or jetpacks.

But then you think about all the awesome technology we already do have that they never really predicted at all. Even something like GPS that might appear really ordinary, is actually pretty revolutionary. We can have a little computer in our pocket that can tell us pretty precisely where exactly in the world we are!


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