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@NASA   
       
       
   Regards,   
       
   Roger   
      
   --- D'Bridge 3.99   
    * Origin: NCS BBS - Houma, LoUiSiAna (1:3828/7)