"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. 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.
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.
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We think that 3200 Pantheon may be a comet that's exhausted all of it's "stuff". A dead comet so to speak. But, last night's show was spectacular. Last year we had to deal with a full moon and didn't get much of a show. But this year the lack of a moon made the show so amazing.
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