Comet Corpses in the Solar Wind   
       
   Jan. 20, 2012: A paper published in today's issue of Science raises an   
   intriguing new possibility for astronomers: unearthing comet corpses in the   
   solar wind.  The new research is based on dramatic images of a comet   
   disintegrating in the sun's atmosphere last July.   
       
   Comet Lovejoy grabbed headlines in Dec. 2011 when it plunged into the sun's   
   atmosphere and emerged again relatively intact.  But it was not the first   
   comet to graze the sun. Last summer a smaller comet took the same trip with   
   sharply different results. Comet C/2011 N3 (SOHO) was completely destroyed on   
   July 6, 2011, when it swooped 100,000 km above the stellar surface.  NASA's   
   Solar Dynamics Observatory (SDO) recorded the disintegration.   
       
       
   Comet C/2011 N3 fragments as it passes through the sun's atmosphere on July 6,   
   2011. Credit: Solar Dynamics Observatory/K. Schrijver et al [larger image]     
   "For the first time, we saw a comet move across the face of the sun and   
   disappear," says Dean Pesnell, a co-author of the Science paper and Project   
   Scientist for SDO at the Goddard Space Flight Center.  "It was unprecedented."   
       
   In Jan. 20th issue of Science, the research team reported their analysis of   
   the SDO images.   
       
   A key finding was the amount of material deposited into the sun's atmosphere.    
   "The comet dissolved into more than a million tons of electrically charged   
   gas," says Pesnell.  "We believe these vapors eventually mixed with the solar   
   wind and blew back into the solar system."   
       
   Pesnell says it might be possible to detect such "comet corpses" as they waft   
   past Earth. Comets are rich in ice (frozen H2O), so when they dissolve in the   
   hot solar atmosphere, the gaseous remains contain plenty of oxygen and   
   hydrogen. A solar wind stream containing extra oxygen could be a telltale sign   
   of a disintegrated comet. Other elements abundant in comets would provide   
   similar markers.   
       
   Comet corpses are probably plentiful.  There's a busy family of comets known   
   as "Kreutz sungrazers," thought to be fragments of a giant comet that broke   
   apart hundreds of years ago. Every day or so, SOHO sees one plunge into the   
   sun and vanish. Each disintegration event creates a puff of comet vapor that   
   might be detectable by spacecraft sampling the solar wind.   
       
   Why bother? Researchers are beginning to think of sungrazers as 'test   
   particles' for studying the sun's atmosphere--kind of like tossing rocks into   
   a pond.  A lot can be learned about the pond by studying the ripples.   
       
       
   An extreme ultraviolet movie recorded by SDO shows comet Comet C/2011 N3   
   flying through the sun's atmosphere. [Quicktime video] Indeed, SDO observed   
   some extraordinary interactions between the sun and the doomed comet.  As   
   C/2011 N3 (SOHO) moved through the hot corona, cold gas lifted off the comet's   
   nucleus and rapidly (within minutes) warmed to more than 500,000K, hot enough   
   to shine brightly in SDO's extreme ultraviolet telescopes.   
       
   "The evaporating comet gas was glowing as brightly as the sun behind it,"   
   marvels Pesnell.   
       
   The gas was also rapidly ionized by a process called "charge exchange," which   
   made the gas responsive to the sun's magnetic field. Caught in the grip of   
   magnetic loops which thread the solar corona, the comet's ionized tail wagged   
   back and forth wildly in the moments before final disintegration.   
       
   Watching this kind of sun-comet interaction could reveal new things about the   
   thermal and magnetic structure of the solar atmosphere.  Likewise, measuring   
   how long it takes for "comet corpses" to reach Earth, and then sampling the   
   gases when they arrive, could be very informative.   
       
   "Before SDO, no one dreamed we could observe a comet disintegrate inside the   
   sun's atmosphere," says Pesnell who confesses that even he was a skeptic. But   
   now, "I'm a believer."   
       
   The original research described in this story may be found in the Jan. 20th   
   edition of Science: Destruction of Sun-grazing comet C/2011 N3 (SOHO) by C. J.   
   Schrijver, J. C. Brown, K. Battams, P. Saint-Hilaire, W. Liu, H. Hudson, and   
   W. D. Pesnell   
       
       
   Author:Dr. Tony Phillips| Production editor: Dr. Tony Phillips | Credit:   
   Science@NASA   
       
   More Information   
   Comet Lovejoy Plunges into the Sun and Survives -- Science@NASA   
       
   Comet's Demise Observed for the First Time -- videos from SDO   
       
   Some Comets Like it Hot -- Science@NASA feature story   
       
   Sungrazing Comet -- ScienceCast video   
       
   Some Comets Like it Hot -- ScienceCast video   
       
       
   Regards,   
       
   Roger   
      
   --- D'Bridge 3.73   
    * Origin: NCS BBS (1:3828/7)