A NASA astronomer has said the upcoming Geminid meteor shower – probably best late night December 13, or early morning December 14 – defies explanation.
“The Geminids are my favorite,” NASA astronomer Bill Cooke said in a recent post at NASA Science, “because they defy explanation.”
The Geminid meteor shower comes every year in December. It’s one of the best meteor showers of the year. Most meteors in annual showers are thought to originate as debris left behind by comets. But the parent of the Geminid meteor shower is not a comet. It’s a rocky object – more like an asteroid – named 3200 Phaethon by astronomers.
Astronomers say this object sheds very little dusty debris—not nearly enough to explain the Geminids. This makes the Geminids the 900-pound gorilla of meteor showers, while 3200 Phaethon is more of a 98-pound weakling, according to NASA scientists.
3200 Phaethon was discovered in 1983. Astronomers classified it as an asteroid and gave it an asteroid’s name. But asteroids aren’t known to spawn meteor showers. Instead, meteor showers typically originate in comets, which are icy bodies – fragile – and more likely to leave a trail of debris behind them .
3200 Phaethon resembles a main belt asteroid – one of the largest asteroids – Pallas. Some astronomers have speculated that 3200 Phaethon might be the result a collision of another body with Pallas long ago. But researchers who have looked carefully at the orbits of Geminid meteoroids and concluded that they were ejected from 3200 Phaethon when Phaethon was close to the sun—not when it was out in the asteroid belt breaking up with Pallas. Another mystery!
The orbit of 3200 Phaethon brings it inside Mercury’s orbit every 1.4 years. A recent idea is that 3200 Phaethon might receive a regular blast of heat from the sun – when it swings closest to our star. That extra heat might boil jets of dust into the Geminid stream.
But the mystery isn’t solved yet. Astronomers still can’t explain the amount of dust 3200 Phaethon needs to keep the Geminid meteor stream replenished over time.
So the Geminid meteor shower continues to defy explanation – as it delights sky watchers every year around December 13/14. Be sure to watch in 2010. The morning of December 14 will probably be best!