The Great Daylight Fireball (also known as the Grand Teton Meteor) was an Earth-grazing fireball that passed within 57 kilometres (35 mi; 187,000 ft) of Earth's surface at 20:29 UTC on August 10, 1972. It entered Earth's atmosphere at a speed of 15 kilometres per second (9.3 mi/s)[2] 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.[3] An eyewitness to the event, located in Missoula, Montana, saw the object pass directly overhead and heard a double sonic boom. The smoke trail lingered in the atmosphere for several minutes.
| Date | August 10, 1972 |
|---|---|
| Location | Northern America |
| External media | |
|---|---|
| Images | |
 Earthgrazer:The Great Daylight Fireball of 1972 (Credit & Copyright: Antarctic search for meteorites program, Case Western Reserve University, James M. Baker)[1] | |
| Video | |
 Grand Teton Meteor Near Miss! |
The atmospheric pass modified the object's mass and orbit around the Sun. A 1994 study found that it is probably still in an Earth-crossing orbit and predicted that it would pass close to Earth again in August 1997.[3][4] However, the object has not been observed again and so its post-encounter orbit remains unknown.[5]
Description
Analysis of its appearance and trajectory showed the object was about 3 to 14 meters (10 to 46 feet) in diameter, depending on whether it was a comet made of ice or a stony and therefore denser asteroid.[2][6] Other sources identified it as an Apollo asteroid in an Earth-crossing orbit that would make a subsequent close approach to Earth in August 1997.[3] In 1994, Czech astronomer Zdeněk Ceplecha reanalysed the data and suggested the passage would have reduced the asteroid's mass to about a third or half of its original mass, reducing its diameter to 2 to 10 meters (7 to 33 feet).[6]
The object was tracked by military surveillance systems and sufficient data obtained to determine its orbit both before and after its 100-second passage through Earth's atmosphere. Its velocity was reduced by about 800 metres per second (1,800 mph) and the encounter significantly changed its orbital inclination from 15 degrees to 7 degrees.[2] If it had not entered at such a grazing angle, this meteoroid would have lost all its velocity in the upper atmosphere, possibly ending in an airburst, and any remnant would have fallen at terminal velocity.[7]
See also
References
Further reading
- Abe, S.; Borovicka, J.; Spurny, P.; Koten, P.; Ceplecha, Z.; Tamagawa, T (18–22 September 2006). "Earth-grazing fireball on March 29, 2006". European Planetary Science Congress 2006 (abstract). Berlin: 486. Bibcode:2006epsc.conf..486A.
the first and second Earth-grazing fireballs observed on August 10, 1972 (Jacchia, 1974; Ceplecha, 1979) and on October 13, 1990 (Borovicka and Ceplecha, 1992)
- Abe, Shinsuke; et al. (2006). "Earth-grazing fireball on March 29, 2006" (PDF). European Planetary Science Congress 2006: 486. Bibcode:2006epsc.conf..486A. Retrieved 2008-07-07.
full details: orbit, charts, spectra, composition
External links
- US19720810 (Daylight Earth grazer) orbital characteristics from Global Superbolide Network Archive, 2000
- Fireball, meteorite, bolide, meteor, video and photo link to photos and cine film by Linda Baker
- Earthgrazer: The Great Daylight Fireball of 1972 overview of the event including photo by NASA's Astronomy Picture of the Day
- Astronomical Society of the Pacific: Observation of Meteoroid Impacts by Space-Based Sensors – one of several similar events; includes ground track
- Earth Impact Calculator