Sunday, April 25, 2004
When Meteors Explode: Full Account of a Wild Chicago Night "It hit the atmosphere at about 40,000 mph,' Simon said. 'At this great speed, air pressure builds up in front of the object and is much greater than the pressure behind it. This will pull apart many meteors, especially if they already had some cracks. This object probably went though four fragmentation events as it passed through the atmosphere.'

Tremendous heat created by the pressure lit much of the object in a fiery display.

Park Forest resident Noe Garza was asleep when a fragment burst through his ceiling, sliced some window blinds, then bounced across the room and broke a mirror. 'I thought somebody was breaking in,' Garza told a new agency the next day. 'It was a big bang. I can't really describe it.'

Another resident whose home was hit said the room lit up and it sounded like a plane had crashed.

Simon's team examined hundreds of fragments -- 65 pounds worth that were picked up and delivered to the scientists -- to estimate the original rock's size and weight.

The measurements are difficult to pin down, he explained, because a lot of fragments probably hit wooded areas and were not found. And some of the original meteor was probably broken into particles too small to notice. The scientists also analyzed the fragments for a certain radioactive form of cobalt, which can reveal the rock's minimum size. 'If the object is too small [while in space for eons] the cosmic rays will just pass through and not make 60 cobalt,' Simon said.

He said the original rock weighed at least 1,980 pounds as it entered the atmosphere. Long ago, the analysis shows, it was probably heated for a long period of time inside a larger parent asteroid. That asteroid then broke apart, again a long time ago, perhaps in a collision with another asteroid."

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