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rock comet meteor shower presented by

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science at nasa

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every year in mid-december astronomers

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look up in the sky and witness a mystery

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it announces itself with a flurry of

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shooting stars

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for several nights in a row

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dozens to hundreds of meteors per hour

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cut across the glistening constellations

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of winter each one a piece of a puzzle

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waiting to be solved

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it's the geminid meteor shower set to

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peak on december 13th and 14th says bill

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cook of nasa's meteoroid environment

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office

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although the geminids come every year we

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still don't fully understand them most

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meteor showers are caused by icy comets

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which spew jets of meteoroids when they

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are heated by sunlight

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a recent example the orionid meteor

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shower of october was caused by halley's

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comet

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the geminids are different

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the parent is not a comet but a weird

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rocky object named 3200 phaethon

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when 3200 phaethon was discovered in

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1983 by nasa's iris satellite

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astronomers quickly realized that they

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had found the source of the geminids

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the orbit of 3200 phaethon was such a

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close match to that of the geminid

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debris stream

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no other conclusion was possible

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yet here was a puzzler

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everything about 3200 phaethon suggests

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it's an asteroid not a typical comet

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in fact 3200 phaethon resembles main

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belt asteroid palace so much it could

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well be a five kilometer chip off that

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544 kilometer block

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if 3200 phaethon broke apart from

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asteroid palace as some researchers

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believe

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then geminid meteoroids might be debris

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from the breakup speculates cook

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there is however another possibility

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perhaps 3200 phaethon is a rock comet

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a rock comet is a new kind of object

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being discussed by some astronomers

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it is essentially an asteroid that comes

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very close to the sun so close that

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solar heating scorches dusty debris

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right off its rocky surface

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rock comets could thus grow comet like

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tails made of gravelly debris that

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produce meteor showers on earth

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could this be the answer

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to test the idea researchers turn to

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nasa's twin stereo spacecraft which are

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designed to study solar activity

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in june 2009 stereo watched 3200

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phaethon passing only 15 solar diameters

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from the sun's surface

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what happened next surprised ucla

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planetary scientists david jewett and

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jing li who analyzed the data

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3200 phaethon unexpectedly brightened by

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a factor of two they wrote the most

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likely explanation is that phaethon

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ejected dust perhaps in response to a

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breakdown of surface rocks through

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thermal fracture and decomposition

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cracking of hydrated minerals in the

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intense heat of the sun

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so according to the stereo observations

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3200 phaethon does behave like a rock

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comet

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but jude and lee point out a problem

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the amount of dust 3200 phaeton ejected

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during its sun encounter added a paltry

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0.01 percent to the mass of the geminid

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debris strain

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not enough to keep the debris stream

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stocked up with meteoroids for the

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annual display of shooting stars 3200

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phaethon is not spewing enough dust to

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account for the geminids

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could the rock comet have been more

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active in the past we just don't know

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says cook

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forecasters expect geminid meteor rates

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to top 100 per hour when the shower

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peaks on the moonless nights of december

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13th and 14th 2012.

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cook encourages skywatches to go out

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look up

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and savor the mystery

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