Another meteor shower, another bunch of lunarimpacts...
"OnDec. 14, 2006, we observed at least five Geminid meteorshitting the Moon," reports Bill Cooke of NASA's Meteoroid EnvironmentOffice in Huntsville, AL. Each impact caused an explosion ranging in power from50 to 125 pounds (22 to 56 kilograms) of TNT and a flash of light as bright asa 7th-to-9th magnitude star.
Theexplosions occurred while Earth and Moon were passing through a cloud ofdebris following near-Earth asteroid 3200 Phaethon. This happens every year inmid-December and gives rise to the annual Geminid meteor shower: Streaks oflight fly across the sky as rocky chips of Phaethon hit Earth's atmosphere.It's a beautiful display.
The samechips hitthe Moon, of course, but on the Moon there is no atmosphere to interceptthem. Instead, they hit the ground. "We saw about one explosion perhour," says Cooke.
How does ameteoroid explode? "This isn't the kind of explosion we experience onEarth," explains Cooke. The Moon has no oxygen to support fire orcombustion, but in this case no oxygen is required: Geminid meteoroids hit theground traveling 78,000 mph (35 km/second). "At that speed, even a pebblecan blast a crater several feet wide," says Cooke. "The flash oflight comes from rocks and soil made so hot by impact that they suddenlyglow."
Cooke'sgroup has been monitoring the Moon's nightside (the best place to see flashesof light) since late 2005 and so far they've recorded 19 hits: five or sixGeminids, threeLeonids, one Taurid and a dozen random meteoroids (sporadics). "Theamazing thing is," says Cooke, "we've done it using a pair ofordinary backyard telescopes, 14-inch (35-centimeter), and off-the-shelf CCDcameras. Amateur astronomers could be recording these explosions, too."
Indeed, hehopes they will. The NASA team can't observe 24-7. Daylight, bad weather,equipment malfunctions, vacations--"lots of things get in the way ofmaximum observing." Amateur astronomers could fill in the gaps. Aworldwide network of amateurs, watching the Moon whenever possible, "wouldincrease the number of explosions we catch," he says.
To thatend, Cooke plans to release data reduction software developed specifically foramateur and professional astronomers wishing to do this type of work. (Therelease will be announced on Science@NASAin the near future.) The software runs on an ordinary PC equipped with adigital video card. "If you have caught a lunar meteor on tape, thisprogram can find it. It eliminates the need to stare at hours of black andwhite video, looking for split-second flashes."
More datawill help NASA assess the meteoroid threat as the agency prepares to sendastronauts back to the Moon. Ready to assist? Stay tuned to Science@NASA forfurther instructions.