NASA Spacecraft Closes in on Comet Tempel 1   
       
   February 9, 2011: NASA is about to discover how solar heat devours a comet.   
       
   Stardust-NExT chases a comet, an artist's concept. [more] "For the first time,   
   we'll see the same comet before and after its closest approach to the sun,"   
   explains Joe Veverka, principal investigator for NASA's Stardust-NExT mission.   
       
   The comet is Tempel 1, which NASA's Deep Impact probe visited in 2005. Now   
   another NASA spacecraft, Stardust-NExT, is closing in for a second look on   
   Valentine's Day, Feb. 14, 2011. The two visits bracket one complete orbit of   
   the comet around the sun--and a blast of solar heat.   
       
   "Close encounters with the sun never go well for a comet," says Veverka.   
   "Fierce solar heat vaporizes the ices in the comet's core, causing it to spit   
   dust and spout gas. The cyclic loss of material eventually leads to its   
   demise."   
       
   Researchers suspect the flamboyant decay doesn't happen evenly all over a   
   comet's surface*, but until now they've lacked a way to document where,   
   exactly, it does occur. Stardust NExT will image some of the same surface   
   areas Deep Impact photographed 6 years ago, revealing how these areas have   
   changed and where material has been lost.   
       
   "Deep Impact gave us tantalizing glimpses of Temple 1," says Veverka. "And we   
   saw strange and unusual things we'd like a closer look at."   
       
   At a January 2011 press conference, Veverka and other Stardust-NExT team   
   members listed the features they're most interested in seeing again:   
       
   For starters, parts of the comet's surface are layered like pancakes.   
       
   "Earth has layers because water and wind move dirt and debris around here, but   
   layering on a comet was a surprise - and a mystery," says Veverka.   
   [...]   
   Pancake-layers and a possible powdery flow are among the surface features of   
   interest highlighted in this July 4, 2005, Deep Impact photo of Comet Tempel   
   1. The bright flash is where Deep Impact dropped an 820 lb copper projectile   
   onto the comet. Stardust-NExT could get a first look at the aftermath of the   
   blast. [more]   
       
   "One idea is that two protocometary bodies collided at low speeds and smushed   
   together to form something like a stack of flapjacks," says Pete Shultz,   
   Stardust-NExT co-investigator.   
       
   Is that right? Data obtained by Stardust-NExT will provide clues and possibly   
   reveal what made the "comet pancakes."   
       
   Another area intrigues the research team even more.   
       
   "There's a large plateau that looks like a flow," says Shultz. "If it really   
   is a flow, it means there was recently gas and dust emanating from the   
   [surface]."   
       
   Stardust-NExT will reveal how the plateau has changed (Is it flowing?),   
   helping the team determine its origin. Whatever their origin, the plateau and   
   layering show that comets have a much more complicated geologic history than   
   previously thought.   
   [...]   
   A close-up view of a possible flow on Tempel 1. [more] "Tempel 1 is not just a   
   fuzzy ball," says Shultz. "It has history."   
       
   It's a history NASA has had a hand in. During its 2005 visit, Deep Impact   
   dropped an 820-pound projectile into the comet's core. In a development that   
   surprised mission scientists, the impact excavated so much material that the   
   underlying crater was hidden from view. Deep Impact's cameras were unable to   
   see through the enormous cloud of dust the impactor had stirred up. Stardust   
   NExT could provide a long anticipated look at the impact site.   
       
   "The dust has settled there, so if the right part of the comet is facing us,   
   we could see the crater and learn its size," says Veverka. "That would answer   
   some key questions. For instance, is a comet's surface hard or soft?"   
       
   In a future mission, a spacecraft may land on a comet and gather samples for   
   analysis. To design a suitable lander, researchers need to know what kind of   
   surface it would land on. They'll also need to know which tools to send -   
   drills for hard surfaces or scoops for something softer.   
       
   Like Deep Impact, the Stardust spacecraft has already had a productive career.   
   Launched in 1999, it approached Comet Wild 2 close enough in 2004 to image its   
   feature-rich surface and even gather dust particles from the comet's   
   atmosphere. (A key finding in the sample was the amino acid glycene - a   
   building block of life.)   
       
   "We could have just let this old spacecraft rest on those laurels, leaving it   
   to forever orbit the sun," says Veverka. "But instead, we're doing first-class   
   comet science with it -- again."   
       
   As for Tempel 1, a hungry sun awaits.   
       
       
   Author: Dauna Coulter | Editor: Dr. Tony Phillips | Credit: Science@NASA   
       
   More Information   
   Stardust NExT -- home page   
       
   Stardust-NExT: A Comet "Before and After"   
       
   Punching a Hole in a Comet: Take 2 -- Science@NASA   
       
   *Scientists estimate that a comet's surface is diminished an average of 5 to 6   
   feet of during each "date" with the sun, and the loss is not uniform.   
   "Typically only 10 to 20 percent of a comet's surface is active, so those   
   areas could lose as much as 50 to 60 feet," explains Veverka. "That means   
   comets are not uniform on the inside either - some places are icier, some   
   rockier."   
       
       
   Regards,   
       
   Roger   
      
   --- D'Bridge 3.59   
    * Origin: NCS BBS (1:3828/7)