Comet ISON Meteor Shower   
       
   April 19, 2013: Anticipation is building as Comet ISON plunges into the inner   
   solar system for a close encounter with the sun in November 2013. Blasted at   
   point-blank range by solar radiation, the sungrazer will likely become one of   
   the finest comets in many years.   
       
   When NASA's Swift spacecraft observed the comet in January 2013, it was still   
   near the orbit of Jupiter, but already very active. More than 112,000 pounds   
   of dust were spewing from the comet's nucleus every minute.   
       
   It turns out, some of that dust might end up on Earth.   
       
   http://www.youtube.com/watch?v=_eSYxvUWwVk   
       
   In a new ScienceCast video, experts discuss what might happen if Comet ISON   
   peppers Earth's atmosphere with dust. Play itVeteran meteor researcher Paul   
   Wiegert of the University of Western Ontario has been using a computer to   
   model the trajectory of dust ejected by Comet ISON, and his findings suggest   
   that an unusual meteor shower could be in the offing.   
       
   "For several days around January 12, 2014, Earth will pass through a stream of   
   fine-grained debris from Comet ISON," says Wiegert. "The resulting shower   
   could have some interesting properties.   
       
   According to Wiegert's computer models, the debris stream is populated with   
   extremely tiny grains of dust, no more than a few microns wide, pushed toward   
   Earth by the gentle radiation pressure of the sun. They will be hitting at a   
   speed of 56 km/s or 125,000 mph. Because the particles are so small, Earth's   
   upper atmosphere will rapidly slow them to a stop.   
       
   "Instead of burning up in a flash of light, they will drift gently down to the   
   Earth below," he says.   
       
   Don't expect to notice. The invisible rain of comet dust, if it occurs, would   
   be very slow. It can take months or even years for fine dust to settle out of   
   the high atmosphere.   
       
   While the dust is "up there," it could produce noctilucent clouds (NLCs).   
       
   Paul Wiegert's model of the Comet ISON debris stream: AVI movieNLCs are icy   
   clouds that glow electric-blue as they float more than 80 km above Earth's   
   poles. Recent data from NASA's AIM spacecraft suggests that NLCs are seeded by   
   space dust. Tiny meteoroids act as nucleating points where water molecules   
   gather; the resulting ice crystals assemble into clouds at the edge of space   
   itself.   
       
   This is still speculative, but Comet ISON could provide the seeds for a   
   noctilucent display. Electric-blue ripples over Earth's polar regions might be   
   the only visible sign that a shower is underway.   
       
   Wiegert notes another curiosity: "The shower is going to hit our planet from   
   two directions at once."   
       
   When Earth passes through the debris stream, we will encounter two populations   
   of comet dust. One swarm of dust will be following the Comet ISON into the   
   sun. Another swarm will be moving in the opposite direction, pushed away from   
   the sun by solar radiation pressure. The streams will pepper opposite sides of   
   Earth simultaneously.   
       
   "In my experience, this kind of double whammy is unprecedented," says Wiegert.   
       
   Bill Cooke, lead scientist at NASA's Meteoroid Environment Office, says   
   there's little danger to Earth-orbiting spacecraft. "These particles are just   
   too small to penetrate the walls of our satellites, and they don't stand a   
   chance against the heavy shielding of the ISS." However, he adds, mission   
   operators will be alert around January 12th for possible anomalies.   
       
   Sky watchers should probably be alert, too. The odds of seeing anything are   
   low, but Comet ISON could prove full of surprises.   
       
   Credits:   
       
   Author: Dr. Tony Phillips | Production editor: Dr. Tony Phillips | Credit:   
   Science@NASA   
       
   More information:   
       
   Comet of the Century?  -- ScienceCast video about Comet ISON   
       
   NASA's Swift Sizes Up Comet ISON -- press release   
       
   The NASA Comet ISON Observing Campaign -- get involved!   
       
       
   Regards,   
       
   Roger   
      
   --- D'Bridge 3.91   
    * Origin: NCS BBS - Houma, LoUiSiAna (1:3828/7)