Hubble Observes Aftermath of Possible Asteroid Collision   
       
   Oct. 13, 2010:  Astronomers using NASA's Hubble Space Telescope have captured   
   rare images of a suspected asteroid collision. The snapshots show a bizarre   
   X-shaped object at the head of a comet-like trail of material. Their findings   
   will be published in the Oct. 14th issue of Nature.   
       
   In January 2010, astronomers began using Hubble to track the object, named   
   "P/2010 A2," for five months. At first they thought they had witnessed a fresh   
   asteroid collision, but were surprised to learn the collision occurred in   
   early 2009.   
       
   "We expected the debris field to expand dramatically, like shrapnel flying   
   from a hand grenade," said astronomer David Jewitt of the University of   
   California in Los Angeles, who is a leader of the Hubble observations. "But   
   what happened was quite the opposite. We found that the object is expanding   
   very, very slowly."   
   [...]   
   These three Hubble Space Telescope images, taken over a five-month period,   
   show the odd-shaped debris that likely came from a collision between two   
   asteroids. [more images]   
       
   P/2010 A2 is located in the asteroid belt, a reservoir of millions of rocky   
   bodies between the orbits of Mars and Jupiter. Astronomers estimate that   
   modest-sized asteroids smash into each other about once a year.  Catching   
   asteroids in the act of colliding, however, is difficult because large impacts   
   are rare while small ones, such as the one that produced P/2010 A2, are   
   exceedingly faint. The Lincoln Near-Earth Research (LINEAR) Program Sky Survey   
   first spotted the object's comet-like tail in January 2010, and indeed some   
   astronomers thought it might be a comet. But only Hubble discerned the X   
   pattern, offering unequivocal evidence that something stranger than a comet   
   outgassing had occurred.   
       
   The Hubble images, taken from January to May 2010 with the telescope's Wide   
   Field Camera 3, reveal a point-like object about 400 feet wide, with a long,   
   flowing dust tail behind a never-before-seen X pattern. The tail contains   
   enough dust to make a ball 65 feet wide, most of it blown out of the bigger   
   body by the impact-caused explosion. The 400-foot-wide object in the Hubble   
   image is the remnant of a slightly larger precursor body.   
   [...]   
   A close up of the X-pattern observed by Hubble in Jan. 2010. [more]   
   Astronomers think a smaller rock, perhaps 10 to 15 feet wide, slammed into the   
   larger one. The pair probably collided at high speed, about 11,000 mph, which   
   smashed and vaporized the small asteroid and stripped material from the larger   
   one. Jewitt estimates that the violent encounter happened in February or March   
   2009 and was as powerful as the detonation of a small atomic bomb.   
       
   Astronomers still do not have a good explanation for the X shape. The   
   crisscrossed filaments at the head of the tail suggest that the colliding   
   asteroids were not perfectly symmetrical. Material ejected from the impact,   
   therefore, did not make a symmetrical pattern, a bit like the ragged splash   
   made by throwing a rock into a lake. Larger particles in the X disperse very   
   slowly and give this structure its longevity.   
       
   Astronomers plan to use Hubble again next year to view the object. Jewitt and   
   his colleagues hope to see how far the dust has been swept back by the sun's   
   radiation and how the mysterious X-shaped structure has evolved.   
       
   Stay tuned!   
       
       
   Editor: Dr. Tony Phillips | Credit: Science@NASA   
       
   More Information   
   For images, movies, and more information about asteroid encounter P/2010 A2,   
   visit: http://hubblesite.org/news/2010/34   
   Although the Hubble images give compelling evidence for an asteroid collision,   
   Jewitt says he still does not have enough information to rule out other   
   explanations for the peculiar object. In one such scenario, a small asteroid's   
   rotation increases from solar radiation and loses mass, forming the comet-like   
   tail.   
       
   "These observations are important because we need to know where the dust in   
   the solar system comes from, and how much of it comes from colliding asteroids   
   as opposed to 'outgassing' comets," Jewitt said.  "We also can apply this   
   knowledge to the dusty debris disks around other stars, because these are   
   thought to be produced by collisions between unseen bodies in the disks.   
   Knowing how the dust was produced will yield clues about those invisible   
   bodies."   
       
       
   Regards,   
       
   Roger   
      
   --- D'Bridge 3.55   
    * Origin: NCS BBS (1:3828/7)