Is Vesta the "Smallest Terrestrial Planet?"   
       
   Dec 9, 2011: NASA's Dawn spacecraft spent the last four years voyaging to   
   asteroid Vesta - and may have found a planet.   
       
   Vesta was discovered over two hundred years ago but, until Dawn, has been seen   
   only as an indistinct blur and considered little more than a large, rocky   
   body. Now the spacecraft's instruments are revealing the true complexity of   
   this ancient world.   
       
   "We're seeing enormous mountains, valleys, hills, cliffs, troughs, ridges,   
   craters of all sizes, and plains," says Chris Russell, Dawn principal   
   investigator from UCLA. "Vesta is not a simple ball of rock. This is a world   
   with a rich geochemical history. It has quite a story to tell!"   
       
   http://www.youtube.com/watch?v=_JBNkts5YXA   
       
   Like Earth and other terrestrial planets, Vesta has ancient basaltic lava   
   flows on the surface and a large iron core. It also has tectonic features,   
   troughs, ridges, cliffs, hills and a giant mountain. False colors in this   
   montage represent different rock and mineral types. [more] [video]   
   In fact, the asteroid is so complex that Russell and members of his team are   
   calling it the "smallest terrestrial planet."   
       
   Vesta has an iron core, notes Russell, and its surface features indicate that   
   the asteroid is "differentiated" like the terrestrial planets Earth, Mercury,   
   Mars, and Venus.   
       
   Differentiation is what happens when the interior of an active planet gets hot   
   enough to melt, separating its materials into layers. The light material   
   floats to the top while the heavy elements, such as iron and nickel, sink to   
   the center of the planet.   
       
   Researchers believe this process also happened to Vesta.   
       
   The story begins about 4.57 billion years ago, when the planets of the Solar   
   System started forming from the primordial solar nebula. As Jupiter gathered   
   itself together, its powerful gravity stirred up the material in the asteroid   
   belt so objects there could no longer coalesce. Vesta was in the process of   
   growing into a full-fledged planet when Jupiter interrupted the process.   
       
   http://www.youtube.com/watch?v=_JBNkts5YXA   
       
   Like Earth and other terrestrial planets, Vesta is differentiated into layers.   
   Although Vesta's growth was stunted, it is still differentiated like a true   
   planet.   
       
   "We believe that the Solar System received an extra slug of radioactive   
   aluminum and iron from a nearby supernova explosion at the time Vesta was   
   forming," explains Russell. "These materials decay and give off heat. As the   
   asteroid was gathering material up into a big ball of rock, it was also   
   trapping the heat inside itself."   
       
   As Vesta's core melted, lighter materials rose to the surface, forming   
   volcanoes and mountains and lava flows.   
       
   "We think Vesta had volcanoes and flowing lava at one time, although we've not   
   yet found any ancient volcanoes there," says Russell. "We're still looking.   
   Vesta's plains seem similar to Hawaii's surface, which is basaltic lava   
   solidified after flowing onto the surface.   
       
   Vesta has so much in common with the terrestrial planets, should it be   
   formally reclassified from "asteroid" to "dwarf planet"?   
       
   "That's up to the International Astronomical Union, but at least on the   
   inside, Vesta is doing all the things a planet does."   
       
   If anyone asks Russell, he knows how he would vote.   
       
       
   Author: Dauna Coulter | Editor: Dr. Tony Phillips | Credit: Science@NASA   
       
   More Information   
       
   Dawn will depart Vesta in summer 2012 for Ceres, where it will arrive in 2015.   
   Dawn's mission to Vesta and Ceres is managed by the Jet Propulsion Laboratory,   
   Pasadena, Calif., for NASA's Science Mission Directorate in Washington. JPL is   
   a division of the California Institute of Technology in Pasadena. Dawn is a   
   project of the directorate's Discovery Program, managed by NASA's Marshall   
   Space Flight Center in Huntsville, Ala.   
       
       
   Regards,   
       
   Roger   
      
   --- D'Bridge 3.64   
    * Origin: NCS BBS (1:3828/7)