Hello All!   
      
   A New Count of Potentially Hazardous Asteroids    
      
   May 16, 2012:  Observations from NASA's Wide-field Infrared Survey Explorer   
   (WISE) have led to the best assessment yet of our solar system's population of   
   potentially hazardous asteroids. Also known as "PHAs," these asteroids have   
   orbits that come within five million miles (about eight million kilometers) of   
   Earth, and they are big enough to survive passing through Earth's atmosphere   
   and cause damage on a regional, or greater, scale.   
      
   The asteroid-hunting portion of the WISE mission, called NEOWISE, sampled 107   
   PHAs to make predictions about the population as a whole. Findings indicate   
   there are roughly 4,700 PHAs, plus or minus 1,500, with diameters larger than   
   330 feet (about 100 meters). So far, an estimated 20 to 30 percent of these   
   objects have been found.    
      
   http://www.nasa.gov/mission_pages/WISE/multimedia/gallery/neowise/pia15627.html   
      
   In this simulated view of the near-Earth asteroid population, potentially   
   hazardous asteroids (PHAs) are denoted in orange. Less dangerous near-Earth   
   asteroids are blue. Earth's orbit is green. [more]    
      
   While previous estimates of PHAs predicted similar numbers, they were rough   
   approximations. NEOWISE has generated a more credible estimate of the objects'   
   total numbers and sizes. Because the WISE space telescope detected the   
   infrared light, or heat, of asteroids, it was able to pick up both light and   
   dark objects, resulting in a more representative look at the entire   
   population.    
      
   "The NEOWISE analysis shows us we've made a good start at finding those   
   objects that truly represent an impact hazard to Earth," said Lindley Johnson,   
   program executive for the Near-Earth Object Observation Program at NASA   
   Headquarters. "But we've many more to find, and it will take a concerted   
   effort during the next couple of decades to find all of them that could do   
   serious damage or be a mission destination in the future."    
      
      
   This orbit diagram illustrates the difference between a PHA and less hazardous   
   near-Earth asteroids (NEA). [more] The new analysis suggests that about twice   
   as many PHAs as previously thought reside in low-inclination orbits, which are   
   roughly aligned with the plane of Earth's orbit.    
      
   "Our team was surprised to find the overabundance of low-inclination PHAs,"   
   said Amy Mainzer, NEOWISE principal investigator, at NASA's Jet Propulsion   
   Laboratory. "Because they will tend to make more close approaches to Earth,   
   these targets can provide the best opportunities for the next generation of   
   human and robotic exploration."    
      
   http://science.nasa.gov/media/medialibrary/2012/05/16/orbits_med.jpg   
      
   The NEOWISE analysis suggests a possible origin for the low-inclinaton PHAs:   
   Many of them could have originated from a collision between two asteroids in   
   the main belt lying between Mars and Jupiter. A larger body with a   
   low-inclination orbit may have broken up in the main belt, causing some of the   
   fragments to drift into orbits closer to Earth and eventually become PHAs.    
      
   The lower-inclination PHAs appear to be somewhat brighter and smaller than   
   other near-Earth asteroids. The discovery that PHAs tend to be bright says   
   something about their composition; they are more likely to be either stony,   
   like granite, or metallic. This type of information is important in assessing   
   the space rocks' potential hazards to Earth. The composition of the bodies   
   would affect how quickly they might burn up in our atmosphere if an encounter   
   were to take place.    
      
   "The NEOWISE project, which wasn't originally planned as part of WISE, has   
   turned out to be a huge bonus," said Mainzer.  "Everything we can learn about   
   these objects helps us understand their origins and fate."   
      
   The NEOWISE results have been accepted for publication in the Astrophysical   
   Journal.    
      
      
   Production editor: Dr. Tony Phillips | Credit: Science@NASA   
      
   More Information    
   The WISE spacecraft scanned the sky twice in infrared light before entering   
   hibernation mode in early 2011. It catalogued hundreds of millions of objects,   
   including super-luminous galaxies, stellar nurseries and closer-to-home   
   asteroids. The NEOWISE project snapped images of about 600 near-Earth   
   asteroids, about 135 of which were new discoveries. Because the telescope   
   detected the infrared light, or heat, of asteroids, it was able to pick up   
   both light and dark objects, resulting in a more representative look at the   
   entire population. The infrared data allowed astronomers to make good   
   measurements of the asteroids' diameters and, when combined with visible light   
   observations, how much sunlight they reflect.   
      
   JPL manages, and operates the Wide-field Infrared Survey Explorer for NASA's   
   Science Mission Directorate, Washington. The principal investigator, Edward   
   Wright, is at UCLA. The mission was competitively selected under NASA's   
   Explorers Program managed by the Goddard Space Flight Center, Greenbelt, Md.   
   The science instrument was built by the Space Dynamics Laboratory, Logan,   
   Utah, and the spacecraft was built by Ball Aerospace & Technologies Corp.,   
   Boulder, Colo. Science operations and data processing and archiving take place   
   at the Infrared Processing and Analysis Center at the California Institute of   
   Technology in Pasadena. Caltech manages JPL for NASA.    
      
   More information is online at http://www.nasa.gov/wise and http:   
   /jpl.nasa.gov/wise .     
      
      
   Regards,   
      
   Roger    
   --- timEd/386 1.10.y2k+   
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