August 10th marks the 40th anniversary of the "Daylight Fireball" which was seen over North America from Utah to Canada. Also called US19720810 or the Great Daylight 1972 Fireball, this Earth-grazing meteoroid passed within 57 kilometers (35 miles) of the surface of the Earth at 20:29 UTC on August 10, 1972. It entered the Earth's atmosphere in daylight over Utah, United States (14:30 local time) and passed northwards leaving the atmosphere over Alberta, Canada. It was seen by many people and recorded on film and by space-borne sensors.
Analysis of its appearance and trajectory showed it was a meteoroid whose size depended on its composition. It would have ranged from about 3 meters (9.8 feet) in diameter, if a carbonaceous chondrite, to 14 meters (46 ft), if made of cometary ices. The meteoroid was in the Apollo asteroid class in an Earth-crossing orbit that would make a subsequent close approach to Earth in August 1997. In 1994, Czech astronomer Zdenek Ceplecha re-analyzed the data and suggested the passage would have reduced the meteoroid's mass to about a third or half of its original mass (reducing its diameter to 2 to 10 meters (6 ft 7 in to 32 ft 10 in).
The meteoroid's 100-second passage through the atmosphere reduced its velocity by about 800 meters per second (2,600 ft/s) and the whole encounter significantly changed its orbital inclination from 15 degrees to 8 degrees.
To learn more about meteors, comets, and asteroids, check out these URLs.
NASA's All Fireball Network (fireballs.ndc.nasa.gov), part of NASA's Meteoroid Environment Office, www.nasa.gov/offices/meo .
Asteroids, Comets, Meteorites (a NASA Asteroid Watch article): www.jpl.nasa.gov/asteroidwatch/asteroids-comets.cfm
NASA's Near-Earth Object (NEO) Program coordinates NASA-sponsored efforts to detect, track and characterize potentially hazardous asteroids and comets that could approach the Earth. To learn more, visit the home page of NASA's Near-Earth Object Program: neo.jpl.nasa.gov .
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