1972 Great Daylight Fireball

The Great Daylight Fireball (also known as the Grand Teton Meteor ) was an Earth-grazing fireball that passed within of Earth's surface at 20:29 UTC on August 10, 1972. It entered Earth's atmosphere at a speed of 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.Observation of Meteoroid Impacts by Space-Based Sensors
Astronomical Society of the Pacific, Edward Tagliaferri, 2003, 'It was first detected by satellite at an altitude of about 73 km, tracked as it descended to about 53 km, and then tracked as it climbed back out of the atmosphere', 'object is still in an Earth-crossing orbit around the Sun and passed close to the Earth again in August 1997' 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.

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. However, the object has not been observed again and so its post-encounter orbit remains unknown.

Description

Analysis of its appearance and trajectory showed the object was about 3–14 m (10–45 ft) in diameter, depending on whether it was a comet made of ice or a stony and therefore denser asteroid. 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. 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 ).Daylight Fireball of August 10, 1972
C. Kronberg, Munich Astro Archive, archived summary by Gary W. Kronk of early analysis and of Zdeněk Ceplecha's paper for Astronomy and Astrophysics in 1994, '3 meters, if a carbonaceous chondrite, or as large as 14 meters, if composed of cometary materials', 'post-encounter ... 2 or 10 meters'

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 and the encounter significantly changed its orbital inclination from 15 degrees to 7 degrees.US19720810 (Daylight Earth grazer)
Global Superbolic Network Archive, 2000, 'Size: 5 to 10 m' 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. [Robert Marcus, H. Jay Melosh, and Gareth Collins
Computing Effects of an Impact on Earth
] by Collins et al. [Collins, Gareth S. et al
Earth Impact Effects Program: A Web-based computer program for calculating the regional environmental consequences of a meteoroid impact on Earth
Meteoritics & Planetary Science 40, Nr 6, 817–840 (2005) "The curvature of the Earth is also ignored."].

See also

* List of asteroid close approaches to Earth

References

Further reading

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External links

US19720810 (Daylight Earth grazer)
orbital characteristics from Global Superbolide Network Archive, 2000


link to photos and cine film by Linda Baker


overview of the event including photo by NASA's Astronomy Picture of the Day


– one of several similar events; includes ground track

Earth Impact Calculator

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August 1972 events in North America
August 1972 events in the United States