New Asteroid Families Discovered   
       
   May 29, 2013: Astronomers using data from NASA's Wide-field Infrared Survey   
   Explorer (WISE) have identified 28 new families of asteroids. The findings are   
   a critical step in understanding the origins of asteroid families, and the   
   collisions thought to have created these rocky clans.   
       
   "We're separating zebras from the gazelles," said Joseph Masiero of NASA's Jet   
   Propulsion Laboratory in Pasadena, Calif., who is lead author of a report on   
   the new study that appears in the Astrophysical Journal. "Before, asteroid   
   family members were harder to tell apart because they were traveling in nearby   
   packs. But now we have a better idea of which asteroid belongs to which   
   family."   
       
   http://www.nasa.gov/mission_pages/WISE/multimedia/pia17016.html   
       
   This artist's conception shows how families of asteroids are created. Image   
   credit: NASA/JPL-Caltech   
       
   An asteroid family is formed when a collision breaks apart a large parent body   
   into fragments of various sizes. Some collisions leave giant craters. For   
   example, the asteroid Vesta's southern hemisphere was excavated by two large   
   impacts. Other smash-ups are catastrophic, shattering an object into numerous   
   fragments, as was the case with the Eos asteroid family. The cast-off pieces   
   move together in packs, traveling on the same path around the sun, but over   
   time the pieces become more and more spread out.   
       
   The new families were found in millions of infrared snapshots from the   
   asteroid-hunting portion of the WISE all-sky survey, called NEOWISE.   
       
   The NEOWISE team looked at about 120,000 main belt asteroids out of the   
   approximately 600,000 known. They found that about 38,000 of these objects,   
   roughly one third of the observed population, could be assigned to 76   
   families, 28 of which are new. In addition, some asteroids thought to belong   
   to a particular family were reclassified.   
       
   "NEOWISE has given us the data for a much more detailed look at the evolution   
   of asteroids throughout the solar system," said Lindley Johnson, the program   
   executive for the Near-Earth Object Observation Program at NASA Headquarters   
   in Washington. "This will help us trace [near-Earth asteroids] back to their   
   sources and understand how some of them have migrated to orbits hazardous to   
   the Earth."   
       
   The next step for the team is to learn more about the original parent bodies   
   that spawned the families.   
       
   "It's as if you have shards from a broken vase, and you want to put it back   
   together to find out what happened," said Amy Mainzer, the NEOWISE principal   
   investigator at JPL. "Why did the asteroid belt form in the first place and   
   fail to become a planet? We are piecing together our asteroids' history."   
       
   More information about the mission is online at: http://www.nasa.gov/wise   
       
   Credits:   
       
   Author: Dr. Tony Phillips | Production editor: Dr. Tony Phillips | Credit:   
   Science@NASA   
       
   JPL, a division of the California Institute of Technology in Pasadena, managed   
   and operated WISE for NASA's Science Mission Directorate. The spacecraft was   
   put into hibernation mode in 2011, after completing its main objectives of   
   scanning the entire sky twice.   
       
   More information:   
       
   Previous knowledge of asteroid family lineages comes from observations of   
   their orbits. NEOWISE also looked at the asteroids' reflectivity to identify   
   family members.   
       
   Asteroids in the same family generally have similar mineral composition and   
   reflect similar amounts of light. Some families consist of darker-colored, or   
   duller, asteroids, while others are made up of lighter-colored, or shinier,   
   rocks. It is difficult to distinguish between dark and light asteroids in   
   visible light. A large, dull asteroid can appear the same as a small, shiny   
   one. The dark asteroid reflects less light but has more total surface area, so   
   it appears brighter.   
       
   NEOWISE could distinguish between the dark and light asteroids because it   
   could detect infrared light, which reveals the heat of an object. The larger   
   the object, the more heat it gives off. When the size of an asteroid can be   
   measured, its true reflective properties can be determined, and a group of   
   asteroids once thought to belong to a single family circling the sun in a   
   similar orbit can be sorted into distinct families.   
       
       
   Regards,   
       
   Roger   
      
   --- D'Bridge 3.94   
    * Origin: NCS BBS - Houma, LoUiSiAna (1:3828/7)