October 15, 2010:  NASA's Deep Impact/EPOXI spacecraft is hurtling toward   
   Comet Hartley 2 for a breathtaking 435-mile flyby on Nov. 4th. Mission   
   scientists say all systems are go for a close encounter with one of the   
   smallest yet most active comets they've seen.   
   [...]   
   Artist's concept of the spacecraft's previous encounter with Comet Tempel 1.   
   [more]   
       
   "There are billions of comets in the solar system, but this will be only the   
   fifth time a spacecraft has flown close enough to one to snap pictures of its   
   nucleus," says Lori Feaga of the EPOXI science team. "This one should put on   
   quite a show!"   
       
   Cometary orbits tend to be highly elongated; they travel far from the sun and   
   then swing much closer. At encounter time, Hartley 2 will be nearing the sun   
   and warming up after its cold, deep space sojourn. The ices in its nucleus   
   will be vaporizing furiously - spitting dust and spouting gaseous jets.   
       
   "Hartley 2's nucleus is small, less than a mile in diameter," says Feaga. "But   
   its surface offgasses at a higher rate than nuclei we've seen before. We   
   expect more jets and outbursts from this one."   
       
   EPOXI will swoop down into the comet's bright coma - the sparkling aura of   
   debris, illuminated by the sun - shrouding the nucleus. The spacecraft's   
   cameras, taking high-resolution (7 meters per pixel at closest approach)   
   pictures all the while, will reveal this new world in all its fizzy glory.   
       
   "We hope to see features of the comet's scarred face: craters, fractures,   
   vents," says Sebastien Besse of the science team. "We may even be able to tell   
   which features are spewing jets!"   
       
   The spacecraft's instruments are already trained on their speeding target.   
       
   "We're still pretty far out, so we don't yet see a nucleus," explains Besse.   
   "But our daily observations with the spectrometer and cameras are already   
   helping us identify the species and amounts of gases in the coma and learn how   
   they evolve over time as we approach."   
   [...]   
   Comet Hartley 2, photographed on Oct. 13 by Science@NASA reader Nick Howes   
   using the 2-meter Faulkes North Telescope in Hawaii.   
       
   The aim of the mission is to gather details about what the nucleus is made of   
   and compare it to other comets. Because comets spend much of their time far   
   from the sun, the cold preserves their composition - and that composition   
   tells a great story.   
       
   "Comets are left-overs from the 'construction' of our solar system," explains   
   Besse. "When the planets formed out of the 'stuff' in the solar nebula   
   spinning around the sun, comets weren't drawn in."   
       
   Researchers study these pristine specimens of the primal solar system to learn   
   something about how it formed, and how it birthed a life-bearing planet like   
   Earth.   
   [...]   
   Click on the EPOXI logo to visit the mission home page.   
       
   "These flybys help us figure out what happened 4 1/2 billion years ago," says   
   Feaga. "So far we've only seen four nucleii. We need to study more comets to   
   learn how they differ and how they are the same. This visit will help,   
   especially since Hartley 2 is in many ways unlike the others we've seen."   
       
   EPOXI will provide not only a birds-eye view of a new world but the best   
   extended view of a comet in history.   
       
   "This spacecraft is built for close encounters. Its instruments and our   
   planned observations are optimized for this kind of mission. When, as Deep   
   Impact, it flew by Tempel 1, it turned its instruments away from the nucleus   
   to protect them from debris blasted up by the impactor. This time we won't   
   turn away."   
       
   The EPOXI team will be waiting at NASA's Jet Propulsion Laboratory.   
       
   "We'll start diving into the data as soon as we receive it," says Feaga.   
   "We'll work round the clock, on our toes the whole time, waiting for the next   
   thing to come down."   
       
   Sounds like it could be intense.   
       
   "It's already intense," says Besse. "We're getting more and more data, but at   
   encounter we'll be flooded!"   
       
   And that will be only the beginning.   
       
       
   Author: Dauna Coulter | Editor: Dr. Tony Phillips | Credit: Science@NASA   
       
   More Information   
   EPOXI -- home page   
       
   Sebastien Besse's EPOXI blog   
       
   On July 4, 2005, NASA's Deep Impact spacecraft's impactor blasted out a crater   
   in the nucleus of Comet Tempel 1. Deep Impact's prime mission was to punch a   
   hole in Tempel 1 and look inside, giving researchers their first glimpse of a   
   comet's internal structure. EPOXI is Deep Impact "recycled." The EPOXI mission   
   uses the already "in flight" Deep Impact flyby spacecraft. The name EPOXI   
   comes from the spacecraft's two extended missions: the extrasolar planet   
   observations, called Extrasolar Planet Observations and Characterization   
   (EPOCh), already completed, and the impending flyby of comet Hartley 2, called   
   the Deep Impact Extended Investigation (DIXI). For the first time scientists   
   will be able to directly compare two different comets with the same cameras,   
   the same science team, and same processes. This eliminates possible systematic   
   variations like calibration difference between instruments. "We'll know we're   
   comparing apples to apples," says Feaga.   
       
   Before Comet Hartley 2, spacecraft have given us close up looks at four   
   cometary nuclei: Halley, Borrelly, Tempel 1, and Wild 2.   
       
       
   Regards,   
       
   Roger   
      
   --- D'Bridge 3.56   
    * Origin: NCS BBS (1:3828/7)