Sundiving Comet Storm   
       
   Jan. 12, 2011:  The sun has just experienced a storm-not of explosive flares   
   and hot plasma, but of icy comets.   
       
   "The storm began on Dec 13th and ended on the 22nd," says Karl Battams of the   
   Naval Research Lab in Washington, DC. "During that time, the Solar and   
   Heliospheric Observatory (SOHO) detected 25 comets diving into the sun. It was   
   crazy!"   
       
   Sundiving comets-a.k.a. "sungrazers"-are nothing new. SOHO typically sees one   
   every few days, plunging inward and disintegrating as solar heat sublimes its   
   volatile ices. "But 25 comets in just ten days, that's unprecedented," says   
   Battams.   
       
   "The comets were 10-meter class objects, about the size of a room or a house,"   
   notes Matthew Knight of the Lowell Observatory in Flagstaff, Arizona. "As   
   comets go, these are considered small."   
   [...]   
   A sundiving "storm-comet" recorded by SOHO and first noticed by Polish comet   
   hunter Michal Kusiak on Dec. 20, 2010. Click to watch a movie of the comet's   
   death plunge.   
       
   SOHO excels at this kind of work. The spacecraft's coronagraph uses an opaque   
   disk to block the glare of the sun like an artificial eclipse, revealing faint   
   objects that no Earth-bound telescope could possibly see. Every day, amateur   
   astronomers from around the world scrutinize the images in search of new   
   comets. Since SOHO was launched in 1996, more than 2000 comets have been found   
   in this way, an all-time record for any astronomer or space mission.   
       
   Battams and Knight think the comet-storm of Dec. 2010 might herald a much   
   bigger sungrazer to come, something people could see with the naked eye,   
   perhaps even during the day.   
       
   "It's just a matter of time," says Battams. "We know there are some big ones   
   out there."   
   [...]   
   Comet Ikeya-Seki, photographed by Roger Lynds at Kitt Peak, Arizona, on the   
   morning of 1965 October 29. [more] Comet Ikeya-Seki is a good example. In 1965   
   it appeared out of nowhere, dove toward the sun and swooped over the stellar   
   surface only 450,000 km away. Because Ikeya-Seki's nucleus was large, about 5   
   km wide, it survived the encounter and emerged as one of the brightest comets   
   of the past thousand years. Japanese observers saw it in broad daylight right   
   beside the morning sun. People watched in amazement as Ikeya-Seki fell into at   
   least three pieces before receding back into the solar system. Similar but   
   lesser sungrazing comets were observed in 1843, 1882, 1963 and 1970.   
       
   These sungrazers are all related to one another. Astronomers call them the   
   "Kreutz family" after the 19th century astronomer Heinrich Kreutz who first   
   studied them as a group. Modern thinking about the family is attributed to   
   Brian Marsden (1937-2010) of the Harvard Minor Planet Center. He analyzed the   
   orbits of Kreutz comets and saw that they probably came from the breakup of a   
   single giant comet in the 12th century, probably the Great Comet of 1106.   
   According to Marsden's work, Ikeya-Seki-class comets and the smaller SOHO   
   sungrazers are just different-sized fragments of that one progenitor.   
       
   Researchers Zdenek Sekanina and Paul Chodas of JPL modeled the fragmentation   
   of the Kreutz progenitor, and in a 2007 issue of the Astrophysical Journal   
   suggested that more big chunks were on the way. Knight's own counting of SOHO   
   sungrazers supports their idea.   
       
   "Since SOHO was launched there has been a trend of increasing numbers of   
   Kreutz sungrazers," he points out. A table in Knight's 2008 PhD thesis shows   
   SOHO detecting 69 sungrazers in 1997 compared to 200 sungrazers in 2010. "The   
   increase is significant and cannot be accounted for by improvements in SOHO or   
   the increasing skill of comet hunters."   
       
   Was Comet Ikeya-Seki preceded by a storm like that of Dec. 2010?   
       
   No one knows.   
       
   "We have not seen a really big Kreutz comet in the era of space-based   
   coronagraphs," notes Knight. "SOHO wasn't around in 1965 to record how many   
   little comets dove into the sun before Ikeya-Seki. It might be 200 comets per   
   year--or it could be 1000. Without more information, we can't know for sure   
   how soon we might be privileged to see one of the real monsters."   
       
   Battams offers this advice: "Stay tuned to SOHO."   
       
       
   Author: Dr. Tony Phillips | Credit: Science@NASA   
       
   More Information   
   SOHO Spots Comet #2000   
       
   Sungrazing Comets -- news and information about sungrazing comets from the   
   Naval Research Lab   
       
       
   Regards,   
       
   Roger   
      
   --- D'Bridge 3.59   
    * Origin: NCS BBS (1:3828/7)