Embers from a Rock Comet
 
Dec. 12, 2014: December has arrived, and for backyard sky watchers that
means one thing:  It is time for the annual Geminid meteor shower. Every
year in early December, Earth passes through a stream of gravelly, dusty
debris from "rock comet" 3200 Phaethon.  This causes a meteor
shower that sometimes lasts more than two weeks.
 
"This year's Geminid meteor shower will peak on Dec. 13th and 14th
with as many as 120 meteors per hour," predicts Bill Cooke, head of
NASA's Meteoroid Environment Office.  "I'm looking forward to a good
display."
 
https://www.youtube.com/watch?v=sT3D6t8VT-k&feature=youtu.be
 
A new ScienceCast video previews the Geminid meteor shower of 2014. Play it
Everyone has heard of "comets"--icy visitors from the outer solar
system that sprout long tails of gas and dust when they come close to the
sun. But what is a rock comet?
 
A "rock comet" is a new kind of object being discussed by
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 that produce meteor
showers on Earth.
 
The source of the Geminid meteor shower, 3200 Phaethon, looks a lot like an
asteroid.  Indeed, it comes from the asteroid belt and its colors resemble
the colors of other asteroids in the rocky zone between Mars and Jupiter.
Yet 3200 Phaethon has an unusual orbit that brings it deep inside the orbit
of Mercury.  When this happens, it brightens and sprouts a little tail in
mimicry of a comet.  A team of astronomers led by Dave Jewitt of UCLA have
been monitoring 3200 Phaethon using NASA's twin STEREO probes. They think
that intense solar heating blasts the asteroid's rocky surface, causing
3200 Phaethon to shed meteoroids like embers spitting off a log in a
roaring campfire.
 
The debris stream of 3200 Phaethon is broad and massive. "Of all the
debris streams Earth passes through every year, the Geminids' is by far the
most massive," says Cooke. "When we add up the amount of dust in
the Geminid stream, it outweighs other streams by factors of 5 to
500."
 
Geminid meteoroids fly out of--you guessed it--the constellation Gemini.
They hit the top of Earth's atmosphere traveling about 35 km/s or 78
thousand mph.  That may sound fast, but it is actually somewhat slow
compared to other meteor showers.  Geminid meteors tend to be leisurely and
bright, producing many fireballs on the nights around the shower's peak.
 
The best time to look, advises Cooke, is probably between local midnight
and sunrise on Saturday, Dec. 13th, and again at the same time on Sunday,
Dec. 14th, when the constellation Gemini is high overhead, spitting bright
embers of a rock comet across a sparkling starry sky.
 
On Dec. 13, Cooke and a team of astronomers from Marshall Space Flight
Center will host an overnight NASA web chat from 10 p.m. to 2 a.m. CST,
answering questions about the Geminid meteor shower.  To join the webchat
on Dec. 13, log into the chat page at:
 
http://www.nasa.gov/connect/chat/geminids_2014.html
 
Credits:
Author:  Dr. Tony Phillips |  Production editor: Dr. Tony Phillips |
Credit: Science{at}NASA
 
 
Regards,
 
Roger

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