Sunday, December 13 brings 2015’s best meteor shower—the Geminids. It’s also the most mysterious. This year, the Moon is absent and conditions are perfect to see a meteor-a-minute all night long if you’re away from city lights!
Oddity number one: Other major meteor showers require observers to wait until midnight for the best fireworks. And even then the meteors are easy to miss because they’re super-fast. Not the Geminids. They’re in full swing by 9 PM and lope along at 22 miles a second. Not quite stuck-in-traffic slow, but only about half the blazing speed of November’s Leonids or August’s Perseids.
Oddity Number Two: What the heck are they? All other showers are debris from comets, skimpy stuff flimsier than ice. Strangely, Geminid meteors are twice as dense, yet nonetheless a bit too lightweight to be bonafide stone or metal asteroid material.
Oddity Number Three: They just got here. All other major meteor showers have been observed for centuries or millennia. But the Geminids were unseen as recently as the mid-1800s. When Lincoln was in the White House, the Geminids started as a modest shower that delivered only 20 meteors per hour. Over time it’s grown increasingly rich. Now it delivers one to two a minute. That usually qualifies as the year’s best display.
Despite decades of searching, the source of this strange shower was unknown until 1983, when NASA’s infrared-detecting satellite found a small body moving in exactly the same path as the meteoroid swarm. Named 3200 Phaethon, it has an oval, 1.4 year orbit that carries it far within the orbit of Mercury and then out past Mars into the asteroid belt. Since Phaethon does not develop a cometlike tail nor shed appreciable material when approaching the sun, it was assumed to be an asteroid, a rocky body.
Fine. Except asteroids don’t disintegrate to produce meteor showers: Curioser and curioser. Nowadays a few researchers continue to believe Phaethon is nonetheless a true asteroid that suffered enough collisions to fill its lopsided orbit with debris. Phaethon is even officially designated an asteroid.
But most astronomers now think that Phaethon is a has-been comet that completely lost its outer covering and is presently just a comet-core.
Either way, no matter which direction you face, the mystery material puts on quite a show. But do try to get away from artificial lights.