Saturday, December 25, 2010

The Geeks of Pompeii

You want a head-scratcher a little closer to home? Try this:
The Geminid meteor shower, which peaks [in early mid-December], is the most intense meteor shower of the year. It lasts for days, is rich in fireballs, and can be seen from almost any point on Earth.
And astronomers can't figure out why.
Most meteor showers come from comets, which spew ample meteoroids for a night of 'shooting stars.' The Geminids are different. The parent is not a comet but a weird rocky object named 3200 Phaethon that sheds very little dusty debris—not nearly enough to explain the Geminids.
The debris stream that produces the Geminids is massive compared to the others through which the Earth passes, but compared to typical comets, 3200 Phaethon, classified as an asteroid, "is more of a 98-lb weakling."

One possible explanation is that when 3200 Phaethon passes inside the orbit of Mercury, which it does every 1.4 years, the Sun boils off debris that becomes part of the Geminid stream. One problem: When researchers observed 3200 Phaethon pass just 13 million miles (21 million km) from the Sun's surface - that's just a little more than one-third the distance from the Sun to Mercury, in other words, damn close - the amount of debris boiled off amounted to only 0.01% of the mass of the Geminid stream, which is not enough to keep the stream from dissipating over time.
Perhaps the rock comet was more active in the past?

"We just don't know," says [NASA astronomer Bill] Cooke. "Every new thing we learn about the Geminids seems to deepen the mystery."
And no matter what the deniers and dodos may say, scientists love a good mystery.

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