Comet Lovejoy Plunges into the Sun and Survives   
       
   Dec. 16, 2011: This morning, an armada of spacecraft witnessed something that   
   many experts thought impossible. Comet Lovejoy flew through the hot atmosphere   
   of the sun and emerged intact.   
       
   "It's absolutely astounding," says Karl Battams of the Naval Research Lab in   
   Washington DC.  "I did not think the comet's icy core was big enough to   
   survive plunging through the several million degree solar corona for close to   
   an hour, but Comet Lovejoy is still with us."   
       
   The comet's close encounter was recorded by at least five spacecraft: NASA's   
   Solar Dynamics Observatory and twin STEREO probes, Europe's Proba2   
   microsatellite, and the ESA/NASA Solar and Heliospheric Observatory.  The most   
   dramatic footage so far comes from SDO, which saw the comet go in (movie) and   
   then come back out again (movie).   
       
   http://science.nasa.gov/media/medialibrary/2011/12/16/lovejoyemerges.m4v   
       
   NASA's Solar Dynamics Observatory caught Comet Lovejoy emerging from its   
   scorching close encounter with the sun. [Entrance movie:Quicktime (22 MB), m4v   
   (0.8 MB)] [Exit movie:Quicktime (26 MB), m4v (0.8 MB)]   
       
   In the SDO movies, the comet's tail wriggles wildly as the comet plunges   
   through the sun's hot atmosphere only 120,000 km above the stellar surface.   
   This could be a sign that the comet was buffeted by plasma waves coursing   
   through the corona.  Or perhaps the tail was bouncing back and forth off great   
   magnetic loops known to permeate the sun's atmosphere.  No one knows.   
       
   "This is all new," says Battams.  "SDO is giving us our first look1 at comets   
   travelling through the sun's atmosphere. How the two interact is cutting-edge   
   research."   
       
   "The motions of the comet material in the sun's magnetic  field are just   
   fascinating," adds SDO project scientist Dean Pesnell of the Goddard Space   
   Flight Center.   "The abrupt changes in direction reminded me of how the solar   
   wind affected the tail of Comet Encke in 2007 (movie)."   
       
   Comet Lovejoy was discovered on Dec. 2, 2011, by amateur astronomer Terry   
   Lovejoy of Australia.  Researchers quickly realized that the new find was a   
   member of the Kreutz family of sungrazing comets.  Named after the German   
   astronomer Heinrich Kreutz, who first studied them, Kreutz sungrazers are   
   fragments of a single giant comet that broke apart back in the 12th century   
   (probably the Great Comet of 1106).  Kreutz sungrazers are typically small   
   (~10 meters wide) and numerous. The Solar and Heliospheric Observatory sees   
   one falling into the sun every few days.   
       
   At the time of discovery, Comet Lovejoy appeared to be at least ten times   
   larger than the usual Kreutz sungrazer, somewhere in the in the 100 to 200   
   meter range.  In light of today's events, researchers are re-thinking those   
   numbers.   
       
   http://science.nasa.gov/media/medialibrary/2011/12/16/lovejoy_c3_anim2.gif   
       
   This coronagraph image from the Solar and Heliospheric Observatory shows Comet   
   Lovejoy receding from the sun after its close encounter. The horizontal lines   
   through the comet's nucleus are digital artifacts caused by saturation of the   
   detector; Lovejoy that that bright! [movie]   
   "I'd guess the comet's core must have been at least 500 meters in diameter;   
   otherwise it couldn't have survived so much solar heating," says Matthew   
   Knight. "A significant fraction of that mass would have been lost during the   
   encounter. What's left is  probably much smaller than the original comet."   
       
   SOHO and NASA's twin STEREO probes are monitoring the comet as it recedes from   
   the sun. It is still very bright and should remain in range of the   
   spacecrafts' cameras for several days to come. Researchers will be watching   
   closely, because there a good chance for more surprises.   
       
   "There is still a possibility that Comet Lovejoy will start to fragment,"   
   continues Battams. "It's been through a tremendously traumatic event;   
   structurally, it could be extremely weak. On the other hand, it could hold   
   itself together and disappear back into the recesses of the solar system."   
       
   "It's hard to say," agrees Knight.  "There has been so little work on what   
   happens to sungrazing comets after perihelion (closest approach).  This   
   continues to be fascinating."   
       
       
   Author:Dr. Tony Phillips| Production editor: Dr. Tony Phillips | Credit:   
   Science@NASA   
       
   More Information   
   Footnote: 1 "When SDO was launched we thought we would see nothing besides the   
   Sun and the dark disks of the Moon, Earth, Venus, and Mercury in our images,"   
   says SDO project scientist Dean Pesnell of GSFC. "No other bright object would   
   be visible because our instruments are designed to look at the Sun. Now we are   
   measuring the mass and composition of comets by turning the comet inside out."   
       
   Solar Dynamics Observatory -- home page   
       
       
   Regards,   
       
   Roger   
      
   --- D'Bridge 3.64   
    * Origin: NCS BBS (1:3828/7)