It followed the same path around the sun as the particles in the Geminid meteoroid stream. To Harvard astronomer Fred Whipple, best known for his “dirty snowball” model of comets ( SN: 3/14/92, p. In October of that year, the satellite discovered a small asteroid. Instead, it was a heat-seeking spacecraft named the Infrared Astronomical Satellite. “I assumed it was an ICBM or something that the Air Force was launching to test,” he says. Jewitt, then a graduate student at Caltech, remembers walking home one January evening when he happened to see a rocket lift off from a military base. In 1983, astronomers finally found the Geminids’ parent. And based on how little the meteoroids slow down when they hit the air, astronomers deduced that Geminid meteoroids are fairly dense, about three times as dense as water and twice as dense as the Perseid meteoroids. Over time, streams spread out, but this one is so narrow it must have formed less than 2,000 years ago and maybe only a few hundred years ago. On top of that, the Geminid meteoroid stream, the ribbon of dust that traces the asteroid’s orbit around the sun, is newer than many other streams. That’s better than most Perseid performances. Nowadays, at the shower’s peak, a single observer under a dark sky can see more than 100 meteors an hour. During the 20th century, however, the shower strengthened. The shower in those days was weak, producing at most only one or two dozen meteors an hour. First reports of their existence came from England and the United States in 1862. Unlike the Perseid meteors, which people have been observing for nearly 2,000 years, the Geminids are relatively new. The Geminid meteors stood out in other ways, too. Still, as comet after comet was linked to different meteor showers, the Geminids remained apart no one knew their source. As these electrons lose energy, they emit the streak of light - the meteor - that looks as though a star has fallen from the sky. The typical meteoroid is no larger than a grain of sand, but it travels so fast that it energizes electrons both in its own atoms as it disintegrates and in atmospheric atoms and molecules. If Earth plows into this long dust stream, we see a fiery shower as the particles hit our atmosphere. These dust particles, called meteoroids, sprinkle along the comet’s orbit like a dandelion gone to seed. When a comet’s ice vaporizes in sunlight, dust grains also fly off the comet. Astronomers later matched most major meteor showers with one comet or another. They connected the well-known Perseid meteors, visible to most of the world every August, with a comet named Swift-Tuttle that had passed Earth four years earlier. Cosmic connectionsĪstronomers first linked a meteor shower to a comet in 1866. They now look forward to the launch of a spacecraft that will image the asteroid’s surface. Three years ago, however, the asteroid swung extra close to Earth and gave scientists their best chance to study the humble space rock. It’s akin to an ugly duckling’s offspring usurping the beautiful swan’s to win first place in a beauty contest.Īstronomers still don’t know the secret to the asteroid’s success in creating a shower that at its peak normally produces more meteors per hour than any other shower of the year. So how can a mere asteroid outdo all of the glamorous comets and spawn a meteor shower that surpasses its rivals? “It remains a mystery,” says David Jewitt, an astronomer at UCLA. In contrast, asteroids have earned the name “vermin of the skies” for streaking through and ruining photographs of celestial vistas by reflecting the sun’s light. Known as the Geminid shower, it strikes every December and arises not from a flamboyant comet but from an ordinary asteroid - the first, but not the last, linked to a meteor shower.Īlthough both comets and asteroids are small objects orbiting the sun, icy comets sprout beautiful tails when their ice vaporizes in the heat of the sun. Most meteor showers occur when Earth slams into debris left behind by a comet.īut not this meteor shower, which is likely to be the most spectacular of the year. On Sunday night, December 13, countless meteors will shoot across the sky as space particles burn up in our atmosphere and meet a fiery end.
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