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Watching Lunar Dust Settle

Understanding the effects of meteorites and space “junk” is important for our colonization of the moon and Mars.

When the SMART-1 (Small Missions for Advanced Research in Technology) spacecraft smashes into the lunar surface on September 3, it will provide some valuable information about the moon – and the frequent impacts that take place there.

A 3-D model of the SMART-1 spacecraft, slated to crash into the moon on September 3. (Credit: European Space Agency)

The European Space Agency (ESA), which built SMART-1, is still enlisting observers to capture images and data during the brief moment when the craft completes its spiraling descent and crashes into the Lake of Excellence (Lacus Excellentiae), a volcanic plain in the moon’s southern mid-latitudes.

Even binoculars might be adequate for detecting the flash of light when the 366-kilogram craft hits the surface at about two kilometers per second. More importantly, though, bigger telescopes with high-speed video or spectroscopic detectors could provide important data about the lunar surface and the dynamics of such impacts in a vacuum.

“We look for fast imaging of the impact and of the associated ejected material, and for spectroscopic analysis – for example, to find hints about the mineralogy of the impact area,” says Bernard Foing, ESA’s project scientist for SMART-1.

Like the Deep Impact mission that smashed into comet Tempel 1 last year, this mission could lead to an improved understanding of the composition of this unexplored region of the moon, and of the strength and material properties of the surface – information that could be useful as NASA prepares for a new generation of human landings on Mars, slated to begin in 2018.

Future “moon-crash” missions could reveal even more. For example, a mission called LCROSS (Lunar Crater Observation and Sensing Satellite) is planned to hit the moon’s polar region in 2009, where some data suggest there may be significant amounts of water-ice in the soil. Analysis of the plume of material ejected by that mission might not only prove the presence of that ice, but also reveal how much there is, and thus whether or not it could be a practical source of drinking water and even rocket fuel for future lunar missions.

Another proposed mission, designed by students at Brown University, could help to answer some fundamental questions about the natural meteorite impacts that occur all the time on the moon as well as on the Earth and other planets.

The mission, dubbed FLASH (First Lunar Appulsion Spacecraft at Hypervelocity), would be the first ever to hit the moon at a speed comparable to natural meteorites, and thus it could provide a highly useful baseline for calibrating what size object it takes to produce a given brightness of the impact flash. That, in turn, would allow better estimates of the number of impacts that occur naturally on the airless moon – something that could become an important safety issue for scientific research instruments on the moon, eventual human exploration, and ultimately permanent lunar bases.

As space exploration missions go, FLASH would be a bargain, costing well under $10 million. It would be the first student-built spacecraft to leave the Earth’s orbit, says Peter Schultz, an impact specialist at Brown University. The impact could be bright enough to reveal a great deal of detail about the composition of the lunar surface, and the brightness of the flash, from an object of precisely known mass and velocity, would provide the first data “to calibrate all those lunar flashes” seen regularly by telescopes equipped with high-speed video and computerized image analysis, says Schultz.

Last November, Robert Suggs of NASA’s Marshall Space Flight Center saw such a lunar flash using a 10-inch telescope – and thousands of amateurs have telescopes that size or larger. Suggs says that few professional astronomers observe the moon any more: “We tend to think of it as a known quantity. But there is still knowledge to be gained there.”

Of course the chances of an astronaut on the moon being hit by a meteorite are vanishingly small. But we don’t know much about how lunar dust is kicked up by impacts and how far it spreads. Because of the potential risks from such dust plumes, which might obscure the view from lunar telescopes or clog the gears of machinery, NASA’s planetary protection officer, John Rummel, says that in the future there will need to be clear rules and procedures for nations, and even private companies, to register plans for lunar impacts, and to make sure they don’t interfere with any other planned lunar activities.

Fortunately, contamination is not a real concern on the moon because the surface has already been determined to be completely sterile. Any terrestrial organisms that might be introduced from spacecraft would not spread or multiply, according to Rummel. From a biological perspective, “the moon is not interesting in itself,” he says, and the only requirement at this time for anyone planning a lunar impact is “to keep track of where it goes.” A central database should be established to catalogue such sites.

Once there start to be active research sites and human landings on the moon, Rummel says, the main point is that “everybody’s going to have to be polite about where they put things” to make sure they don’t contaminate each others’ sites.

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