Another meteor shower, another bunch of lunar
impacts...
"On
Dec. 14, 2006, we observed at least five Geminid meteors
hitting the Moon," reports Bill Cooke of NASA's Meteoroid Environment
Office in Huntsville, AL. Each impact caused an explosion ranging in power from
50 to 125 pounds (22 to 56 kilograms) of TNT and a flash of light as bright as
a 7th-to-9th magnitude star.
The
explosions occurred while Earth and Moon were passing through a cloud of
debris following near-Earth asteroid 3200 Phaethon. This happens every year in
mid-December and gives rise to the annual Geminid meteor shower: Streaks of
light fly across the sky as rocky chips of Phaethon hit Earth's atmosphere.
It's a beautiful display.
The same
chips hit
the Moon, of course, but on the Moon there is no atmosphere to intercept
them. Instead, they hit the ground. "We saw about one explosion per
hour," says Cooke.
How does a
meteoroid explode? "This isn't the kind of explosion we experience on
Earth," explains Cooke. The Moon has no oxygen to support fire or
combustion, but in this case no oxygen is required: Geminid meteoroids hit the
ground traveling 78,000 mph (35 km/second). "At that speed, even a pebble
can blast a crater several feet wide," says Cooke. "The flash of
light comes from rocks and soil made so hot by impact that they suddenly
glow."
Cooke's
group has been monitoring the Moon's nightside (the best place to see flashes
of light) since late 2005 and so far they've recorded 19 hits: five or six
Geminids, three
Leonids, one Taurid and a dozen random meteoroids (sporadics). "The
amazing thing is," says Cooke, "we've done it using a pair of
ordinary backyard telescopes, 14-inch (35-centimeter), and off-the-shelf CCD
cameras. Amateur astronomers could be recording these explosions, too."
Indeed, he
hopes they will. The NASA team can't observe 24-7. Daylight, bad weather,
equipment malfunctions, vacations--"lots of things get in the way of
maximum observing." Amateur astronomers could fill in the gaps. A
worldwide network of amateurs, watching the Moon whenever possible, "would
increase the number of explosions we catch," he says.
To that
end, Cooke plans to release data reduction software developed specifically for
amateur and professional astronomers wishing to do this type of work. (The
release will be announced on Science@NASA
in the near future.) The software runs on an ordinary PC equipped with a
digital video card. "If you have caught a lunar meteor on tape, this
program can find it. It eliminates the need to stare at hours of black and
white video, looking for split-second flashes."
More data
will help NASA assess the meteoroid threat as the agency prepares to send
astronauts back to the Moon. Ready to assist? Stay tuned to Science@NASA for
further instructions.
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