video capture photo
video capture photo

Dec. 9, 2012:  Every year in mid-December, astronomers look up in the sky and witness a mystery. It announces itself with a flurry of shooting stars. For several nights in a row, dozens to hundreds of meteors per hour cut across the glistening constellations of winter, each one a little puzzle waiting to be solved.

“It’s the Geminid meteor shower–set to peak on Dec. 13th and 14th,” says Bill Cooke of NASA’s Meteoroid Environment Office. “Although the Geminids come every year, we still don’t fully understand them.”

A ScienceCast video explores how a “rock comet” can produce a meteor shower like the Geminids.

Most meteor showers are caused by icy comets, which spew jets of meteoroids when they are heated by sunlight. The Geminids are different. The parent is not a comet but a weird rocky object named 3200 Phaethon.

When 3200 Phaethon was discovered in 1983 by NASA’s IRAS satellite, astronomers quickly realized that they had found the source of the Geminids. The orbit of 3200 Phaethon was such a close match to that of the Geminid debris stream, no other conclusion was possible. Yet here was a puzzler: Everything about 3200 Phaethon suggests it is an asteroid.

In fact, 3200 Phaethon resembles main belt asteroid Pallas so much, it could well be a 5-kilometer chip off that 544 km block. “If 3200 Phaethon broke apart from asteroid Pallas, as some researchers believe, then Geminid meteoroids might be debris from the breakup,” speculates Cooke.

There is, however, another possibility: Perhaps 3200 Phaethon is a “rock comet.”

A “rock comet” is a new kind of object being discussed by some astronomers. It is, essentially, an asteroid that comes very close to the sun–so close that solar heating scorches dusty debris right off its rocky surface. Rock comets could thus grow comet-like tails made of gravely debris that produce meteor showers on Earth.

Written by: DR. TONY PHILLIPS  – continue at NASA SCIENCE/SCIENCE NEWS

 

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