What Exploded over Russia?   
       
   Feb. 26, 2013:  When the sun rose over Russia's Ural Mountains on Friday, Feb.   
   15th, many residents of nearby Chelyabinsk already knew that a space rock was   
   coming. Later that day, an asteroid named 2012 DA14 would pass by Earth only   
   17,200 miles above Indonesia. There was no danger of a collision, NASA assured   
   the public.   
       
   Maybe that's why, when the morning sky lit up with a second sun and a shock   
   wave shattered windows in hundreds of buildings around Chelyabinsk, only a few   
   people picking themselves off the ground figured it out right away. This was   
   not a crashing plane or a rocket attack.   
       
   "It was a meteor strike--the most powerful since the Tunguska event of 1908,"   
   says Bill Cooke of NASA's Meteoroid Environment Office.   
       
   http://www.youtube.com/watch?v=-qZ6oiaSm00   
       
   A new ScienceCast video reviews what researchers have learned about the   
   Russian meteor. Play it   
       
   In a coincidence that still has NASA experts shaking their heads, a small   
   asteroid completely unrelated to 2012 DA14 struck Earth only hours before the   
   publicized event. The impactor flew out of the blue, literally from the   
   direction of the sun where no telescope could see it, and took everyone by   
   surprise.   
       
   "These are rare events and it is incredible to see them happening on the same   
   day," says Paul Chodas of NASA's near-Earth Object Program at JPL.   
       
   Researchers have since pieced together what happened. The most telling   
   information came from a network of infrasound sensors operated by the   
   Comprehensive Test Ban Treaty Organization (CTBTO). Their purpose is to   
   monitor nuclear explosions.   
       
   Infrasound is a type of very low-frequency sound wave that only elephants and   
   a few other animals can hear. It turns out that meteors entering Earth's   
   atmosphere cause ripples of infrasound to spread through the air of our   
   planet. By analyzing infrasound records, it is possible to learn how long a   
   meteor was in the air, which direction it traveled, and how much energy it   
   unleashed.   
       
   The Russian meteor's infrasound signal was was the strongest ever detected by   
   the CTBTO network. The furthest station to record the sub-audible sound was   
   15,000km away in Antarctica.   
       
   https://www.youtube.com/watch?v=H-8ij80vs1E   
       
   Listen to the infrasound recording, sped up 135x into the range of human   
   hearing. Play itWestern Ontario Professor of Physics Peter Brown analyzed the   
   data: "The asteroid was about 17 meters in diameter and weighed approximately   
   10,000 metric tons," he reports. "It struck Earth's atmosphere at 40,000 mph   
   and broke apart about 12 to 15 miles above Earth's surface. The energy of the   
   resulting explosion exceeded 470 kilotons of TNT." For comparison, the first   
   atomic bombs produced only 15 to 20 kilotons.   
       
   Based on the trajectory of the fireball, analysts have also plotted its orbit.   
   "It came from the asteroid belt, about 2.5 times farther from the sun than   
   Earth," says Cooke.   
       
   Comparing the orbit of the Russian meteor to that of 2012 DA14, Cooke has   
   shown that there is no connection between the two. "These are independent   
   objects," he says. "The fact that they reached Earth on the same day, one just   
   a little closer than the other, appears to be a complete coincidence." [orbit   
   diagram]   
       
   Infrasound records confirm that the meteor entered the atmosphere at a shallow   
   angle of about 20 degrees and lasted more than 30 seconds before it exploded.   
   The loud report, which was heard and felt for hundreds of miles, marked the   
   beginning of a scientific scavenger hunt. Thousands of fragments of the meteor   
   are now scattered across the Ural countryside, and a small fraction have   
   already been found.   
       
   Preliminary reports, mainly communicated through the media, suggest that the   
   asteroid was made mostly of stone with a bit of iron--"in other words, a   
   typical asteroid from beyond the orbit of Mars," says Cooke. "There are   
   millions more just like it."   
       
   And that is something to think about as the cleanup in Chelyabinsk continues.   
       
       
   Author: Dr. Tony Phillips |Production editor: Dr. Tony Phillips | Credit:   
   Science@NASA   
       
   More Information   
   Russian fireball largest ever detected by infrasound sensors -- CTBTO press   
   release   
       
   Record-setting Asteroid flyby -- a video from Science@NASA   
       
   Why wasn't the russian meteor detected before it entered Earth's atmosphere?   
   -- Bill Cooke answers   
       
       
   Regards,   
       
   Roger   
      
   --- D'Bridge 3.9   
    * Origin: NCS BBS - Houma, LoUiSiAna (1:3828/7)