"It's the Geminid meteor shower," says NASA astronomer Bill Cooke of the Marshall Space Flight Center. "Start watching on Thursday evening, Dec. 13th, around 10 pm local time," he advises. "At first you might not see very many meteors—but be patient. The show really heats up after midnight and by dawn on Friday, Dec. 14th, there could be dozens of bright meteors per hour streaking across the sky."
The Geminids are not ordinary meteors. While most meteor showers come from comets, Geminids come from an asteroid—a near-Earth object named 3200 Phaethon.
"It's very strange," says Cooke. How does an asteroid make a meteor shower?
Comets do it by evaporating. When a comet flies close to the sun, intense heat vaporizes the comet’s "dirty ice" resulting in high-speed jets of comet dust that spew into interplanetary space. When a speck of this comet dust hits Earth's atmosphere traveling ~100,000 mph, it disintegrates in a bright flash of light—a meteor!
Asteroids, on the other hand, don't normally spew dust into space—and therein lies the mystery. Where did Phaethon's meteoroids come from?
One possibility is a collision. Maybe it bumped against another asteroid. A collision could have created a cloud of dust and rock that follows Phaethon around in its orbit. Such collisions, however, are not very likely.
Cooke favors another possibility: "I think 3200 Phaethon used to be a comet."
Exhibit #1 in favor of this idea is
Phaethon's orbit: it is highly elliptical, like the orbit of a typical comet, and brings Phaethon extremely close to the sun, twice as close as Mercury itself. Every 1.4 years, Phaethon swoops through the inner solar system where repeated blasts of solar heat could easily reduce a flamboyant comet to the rocky skeleton we see today.
If this scenario is correct, Phaethon-the-comet may have produced many rich streams of dust that spent hundreds or thousands of years drifting toward Earth until the first Geminid meteors appeared during the US Civil War. Since then, Geminids have been a regular shower peaking every year in mid-December.
3200 Phaethon is now catalogued as a "PHA"—a potentially hazardous asteroid whose path misses Earth's orbit by only 2 million miles. It measures 5 km wide, about half the size of the asteroid or comet that wiped out the dinosaurs 65 million years ago, and can be seen through backyard telescopes—in fact, now is a good time to look:
"3200 Phaethon is flying past Earth just a few days before this year’s Geminid meteor shower," notes Cooke. On Dec. 10th, Phaethon will be about 11 million miles away shining like a 14th magnitude star in the constellation Virgo: ephemeris. That's too dim for the naked eye, he says, but a good target for amateur telescopes equipped with CCD cameras.
Cooke doesn't expect the flyby to boost the Geminids—"11 million miles is too distant to affect meteor rates"—but the Geminids don't really need boosting. "It's always a great shower," he says. "Don't miss it."
Source: by Dr. Tony Phillips, Science@NASA
Related stories:
The 2006 Geminid Meteor Shower
The best meteor shower of the year peaks this week on Dec. 13th and 14th.
Lunar Leonid Strikes
Meteoroids are smashing into the Moon a lot more often than anyone expected. That's the tentative conclusion of Bill Cooke, head of NASA's Meteoroid Environment Office, after his team observed two Leonids hitting the Moon on Nov. 17, 2006. "We've now seen 11 and possibly 12 lunar impacts since we started monitoring the Moon one year ago," says Cooke. "That's about four times more hits than our computer models predicted."
Making A Meteor
NASA's Deep Impact mission is about to smash into comet 9P/Tempel 1 to excavate a crater and probe the comet's internal structure. It's possible, however, that the comet will break into fragments, creating a cloud of meteoroids. That, say astronomers, may not be unnatural.
The best meteor shower of 2004 peaks on Dec. 13th
by Dr. Tony Phillips
Make hot cocoa. Bundle up. Tell your friends: the best
meteor shower of 2004 is about to peak on a long cold December night.
It's the Geminids. The best time to look is Monday night, Dec. 13th. Sky watchers who stay outside for a few hours around midnight can expect to see dozens to hundreds of "shooting stars."
The source of the shower is asteroid 3200 Phaethon. There's a cloud of dust trailing the asteroid and Earth plows through it every year in mid-December. Bits of dust traveling 80,000 mph hit our atmosphere and turn into glowing meteors.
Lunar Geminids
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 lbs of TNT and a flash of light as bright as a 7th-to-9th magnitude star.
