A Major Moon Dust-Up
October 16, 2008
by Seth Shostak, Senior Astronomer, SETI Institute
Like Rodney Dangerfield, dust don’t get no respect. If you make a laundry list of the material contents of the cosmos, you’ll be sure to put stars, planets, gas clouds and dark matter on the ticket. But dust? Who cares about such tiny, sticky bits of carbon, silicon, and other boring stuff?
Well, about a century ago, astronomers began to care. Dust first became a subject for the telescope crowd when they recognized it as an annoyance similar to windshield grime. Back in the day, researchers were looking around the Milky Way, counting the number of stars per square degree in every direction. The purpose of this tedious exercise was to locate our position in the cosmos. (The universe was thought to consist of one giant galaxy.) They found that the counts didn’t vary a great deal, suggesting that we are situated near the middle of things – right downtown.
But in 1930 – when R. J. Trumpler proved that smoky clouds of dust fill the tracts between stars, blocking our view of the Milky Way’s more distant realms – we realized we’d been fooled. Astronomers were chastened to discover that we’re not situated in the Galaxy’s scintillating central regions, but in its sedate suburbs. Dumb dust had gotten in our way.
Today, there’s powdered crud a lot closer to home that’s a worrisome commodity for astronomers – possibly even affecting our future searches for extraterrestrial intelligence. Lunar dust.
Now let’s face it: the moon seems like dullsville to most folks – after all, it’s lacking in several important everyday conveniences, such as water and air. But NASA has a mandate and plans (if not much budget) to go back to the moon, and eventually use it as a springboard for further space exploration – such as sending humans to Mars.
In addition to being a lay-over for trips elsewhere, the moon is a great place to erect telescopes. There’s no churning atmosphere to distort the images in optical scopes, and – if radio is your game – the back side of the moon is the only place in the universe that’s perpetually shielded from the cacophony of terrestrial transmitters. The lunar far side has been proposed as the perfect location for a SETI antenna.
But the dust is worrisome. The moon’s surface is wrapped in a dust layer between four inches to a yard deep – a pulverized blanket produced by a few billion years’ of micrometeorites slamming into the surface. Earth, you’ll note, doesn’t have this ubiquitous granular carpet. Our planet is blessed with weather, including wind and rain, which washes fine particles into rivers and oceans. (This is not to mention the various household sprays that will remove dust from your Louis XIV furniture.)
But without any climate to disturb it, the dust on the moon not only stays where it lays, it also retains its jagged nature – the edges of the grains remain sharp. It’s dust with bite.
“It will get into anything with moving parts,” says Ryan Kobrick, a PhD candidate in the Aerospace Engineering Sciences program at the University of Colorado who’s trying to determine the properties of lunar dust.
“In addition, sunlight charges up the particles, and they cling together. Think of the famous moon-boot photo,” says Kobrick. “Facts are, any piece of equipment could be choked by dust within days.”
It’s a problem that’s undoubtedly escaped your notice and consideration. It’s not, however, trivial.
“You’ll have to design systems with seals, or with gears that are hard enough that they won’t wear,” said Kobrick.
I made an obvious suggestion: if this dust is going to cramp our style, why not simply bulldoze it away? Kobrick acknowledged that this might help for a while, but “the dust would still migrate around and eventually get onto any equipment. Remember, it’s got an electric charge, and the gravity on the moon is lower, too. It will crawl up the surfaces of your structure.”
Is this a show stopper? Do we abandon the moon’s surface as a useless dust bowl?
Kobrick isn’t that pessimistic. “Elevating your equipment will help,” he confides. “And microwaving the surface under your instrument might be a good idea too, since that would melt the dust into a solid mass if the iron content is high enough.”
“But in the end, there’s going to be maintenance. You’re going to need people to clean out the clogs, and repair the inevitable jams.”
I asked Kobrick whether, when you got right down to it, that was the best reason to send humans to the moon: as dust busters.
He laughed. “I didn’t say that! But dusting is definitely going to be on their to-do list.”
Add it to your roster of requisite astronaut skills.