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2009-03-05 12:45:09
The timing could not have been worse for public paranoia: This weekend, only days after a U.S. communications satellite collided with a defunct Russian military sat, a fireball appeared in the Texas sky. This prompted worried calls to authorities from several counties. The Federal Aviation Administration also warned pilots to watch out for falling debris, thinking pieces of the satellites might be plummeting to Earth.
The connection between the fireball and satellite crash, however, turned out to be just coincidence. The Texas fireball was most likely a meteor entering the atmosphere, the FAA now says. Preston Starr, the director of the University of North Texas observatory, told the AP that the meteor would have to have been as big as a pickup truck, and traveling somewhere between 15,000 and 40,000 miles per hour when it entered the atmosphere. That's small time for a meteor astrophysicist David Palmer of the Los Alamos National Laboratory tells PM that such speeds are close to the minimum at which meteors enter Earth's atmosphere. Meteors orbiting the sun at the opposite direction of Earth could enter our atmosphere at up to 150,000 miles per hour. NASA officials say some of the wreckage from last week's satellite crash might fall into the atmosphere and burn up, but those fragments are too slow and too small to create a daytime fireball. The U.S. satellite was only 1200 pounds to begin with, and it and the Russian
orbiter probably broke up into hundreds of pieces too small to be seen with the naked eye.
Though a possible connection to the satellite collision brewed up hubbub over this fireball, meteors are not at all rare, Palmer says. "There are probably a lot more that are seen than are reported in the news," he says. NASA estimates that between 1000 and 10,000 tons of meteoric materials enter Earth's atmosphere every day, and Starr says meteors as large as the one seen over Texas arrive eight to 10 times a year. Palmer says that fireballs seem rarer than they really are because many appear over the ocean or unpopulated areas and go unnoticed, and they often leave little evidence of their existence afterwards. Though this meteor may have been as big as a truck, Starr says, only a tiny fragment maybe as big as a fist would have reached the Earth's surface.
No one has yet found a remnant of the meteor on the ground, which would help lock down the Texas fireball-as-meteor explanation and hopefully halt some of the more questionable claims. According to University of Hawaii at Manoa planetary scientist Edward Scott, there's a good chance that thanks to its low velocity, the meteorite will show up. Meteors give off their energy by burning or breaking up in the atmosphere, he says, but slower-moving ones have the chance to do that with less intensity and therefore avoid vaporizing entirely. Andrew Moseman