Published December 13, 2010
For sky-watchers willing to brave frosty winter temperatures, more than a hundred meteors an hour may fall overnight on December 13 and 14, the peak of the annual Geminid meteor shower.
"The quarter moon will obscure the first part of the show, but once it sets after midnight [your local time], the conditions should be ideal," said Geza Gyuk, an astronomer at the Adler Planetarium in Chicago, Illinois.
"If you can't stay up that late, then after 10 p.m. is okay too, but the later the better."
The missed sleep may be worth it: The Geminids have been rising in intensity and brightness, and the upcoming show may outshine the more famous August Persieds as the best meteor shower of 2010.
"The Geminids have been slowly getting better over the past years, making it one of the best showers," Gyuk said. "And it has become very reliable, so we can expect a fairly nice show."
To See Geminids, Look to the East
Geminid meteors appear to radiate from the shower's namesake constellation, Gemini, the twins from Greek legend. Gemini will rise above the eastern horizon at about 9 p.m. local time, so sky-watchers should face northeast to spot the meteors.
Observers in the Northern Hemisphere will have the advantage, because that's where Gemini will appear high in the night sky, making most of the shooting stars visible.
"For folks in the Southern Hemisphere, it will simply be lower in the sky and hence have a lower rate," Gyuk said.
Dozens of shooting stars should be visible over the course of the entire week. But the main peak of activity will center on the early morning hours of December 14, between about 2 a.m. and dawn.
Geminids Created by Active Asteroid?
Most annual meteor showers happen when Earth passes through clouds of debris left behind by passing comets, causing tons of dust to rain down on the planet in short periods of time.
The particles of dust—most no bigger than grains of sand—enter Earth’s atmosphere at high speed, burning up and superheating the air around them, which then shine with quick streaks of light.
The Geminids are unusual, though, because they're thought to be the only annual meteor shower created by an asteroid-like object: 3200 Phaethon.
Discovered in 1983 by a NASA satellite, Phaethon is a three-mile-wide (five-kilometer-wide) space rock. Its year-and-a-half-long orbit precisely matches the appearance of the Geminids, making the body a prime candidate for the source of the meteors.
But unlike a comet, Phaethon has no tail, it orbits near other asteroids, and its surface colors look more like those of asteroids than comets. So experts have been debating whether that means Phaethon is an ancient comet that has sputtered out or a dusty asteroid that for some reason sheds material near the sun.
According to recent studies, "Phaethon—which was expected to be like a dead comet—is actually more like an activated asteroid," said Humberto Campins, an astronomer at the University of Central Florida who has been studying the weird object.
"Spectral analysis shows that it is a lot like 500-kilometer-wide [310-mile-wide] Pallas, the second largest asteroid in the solar system," Campins said. For instance, both bodies contain minerals known as carbonates and hydrated silicates. Astronomers think Phaethon may be a piece of Pallas that broke off during a long-ago collision.
Using NASA's sun-studying STEREO orbiter, astronomers recently observed Phaethon as it made one of its close approaches to the sun, and they noted an increase in the object's brightness.
"It is because of these close encounters with the sun that it has these outbursts, raising its temperatures well above 1,000 degrees Celsius [1,832 degrees Fahrenheit], where minerals like carbonates become unstable and become explosive," Campins said. (See "Exploding Clays Drive Geminids Sky Show?")
"A cloud of particles end up forming around Phaethon, and eventually these would spread out along the orbit of the asteroid and form the Geminids."
Geminid Meteorites May Be Asteroid Samples
Evidence for this theory may lie even closer to home.
Some of the Geminids hit Earth's atmosphere at such a grazing angle that they may survive atmospheric entry. In fact, the Geminid meteor shower is known to produce slow-moving fireballs caused by baseball- to basketball-size stones.
"It is conceivable that we have meteorites that come from Pallas via Phaethon right here on Earth," Campins said.
"It's amazing to think that we might end up with nature providing us with a kind of sample-return mission to the second largest asteroid in our solar system—and it doesn't cost us anything."
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