The Great Daylight 1972 Fireball

The Great Daylight 1972 Fireball (or US19720810) is an Earth-grazing meteoroid which passed within 57 kilometres 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. [ 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']


Analysis of its appearance and trajectory showed it was a meteoroid about 3 (if a carbonaceous chondrite) to 14 metres (if made of cometary ices) in diameter 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-analysed 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 metres). [ Daylight Fireball of August 10, 1972] C. Kronberg, Munich Astro Archive, archived summary by Gary W. Kronk of early analysis and of Zdenek 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 meteoroid's 100 second passage through the atmosphere reduced its velocity by about 800 metre per second and the whole encounter significantly changed its orbital inclination from 15 degrees to 8 degrees. [ US19720810 (Daylight Earth grazer)] Global Superbolic Network Archive, 2000, 'Size: 5 to 10 m']

The fireball was filmed by a tourist at the Grand Teton National Park in Wyoming using an 8-millimeter color movie camera [ [ Grand Teton Meteor Video] , Youtube]

This was the first Earth grazing fireball observed. As of 2008 only three subsequent Earth grazers have been scientifically observed: the Earth-grazing fireball of October 13, 1990 passing at around 100 kilometres altitude over Czechoslovakia; the possible Earth-grazing fireball on March 29, 2006 over Japan,Abe 2006 (abstract)] and EN070807 (see All known Earth-grazing fireballs).

What if it had impacted?

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. Atmospheric entry of meteoroids is complex and a full calculation requires a full simulation, but a highly simplified calculation can be made using the web-based program [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."] . This table shows how sensitive the result is to the entry angle and composition:

All known Earth-grazing fireballs

Earth-grazing fireballs are a very rare kind of fireballP. Spurný, J. Borovička, Z. Ceplecha and L. Shrbený, Astronomical Institute of the Academy ofSciences, Fričova 298, CZ-251 65 Ondřejov Observatory, Czech Republic [ PRECISE MULTI-INSTRUMENT DATA ON 45 FIREBALLS RECORDED OVER CENTRAL EUROPE IN THE PERIOD 2006-2008] . Retrieved 2008-07-06] caused by a meteoroid that collides with the Earth but survives the collision by passing through, and exiting, the atmosphere. As of 2008 four grazers have been scientifically observed. [Although other grazers have been seen and, rarely, photographed, without specialised scientific observations their orbits cannot be determined. An example is the Leonid grazer over Hawaii in 2001-11-18 -Abe 2006 (PDF)]

* 1913-02-09, a narrow fireball stream led to conclusions a probable natural satellite of Earth had broken up [O'Keefe, John A. 1959. [ A Probable Natural Satellite: The Meteor Procession of February 9 1913] . Journal of the Royal Astronomical Society of Canada, Vol. 53, p.59. Code 1959JRASC..53...59O. Retrieved 2008-07-07]
* 1972-08-10, US19720810 at 15 km/sec above United States and Canada (first scientific observation)
* 1990-10-13, a 40 kilogram, 41.5 km per sec meteoroid passed at 97.9 km above Czechoslovakia [Spurny', P.; Ceplecha, Z.; Borovicka, J. [ Earth-grazing fireball: Czechoslovakia, Poland, October 13, 1990, 03h27m16sUT] . WGN, Vol. 19, Nr. 1, p. 13; (aphelion of its orbit changed from 2.80 AU to 1.80 AU)]
* 2006-03-29, fireball passed 18.8 km per sec through the atmosphere 71.4 km above JapanAbe 2006 (PDF) approximately 100 kg, orbit aphelion reaches Jupiter]
* 2007-08-07, EN070807 passed through with an orbit belonging to the rare Aten asteroid type [EN indicates the European Fireball Network]

ee also

* Record-setting close approaches by asteroids to Earth


*Abe, S. et al. (abstract) [ Earth-grazing fireball on March 29, 2006] European Planetary Science Congress 2006. Berlin, Germany, 18 - 22 September 2006., p.486. code: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. (PDF). [ Earth-grazing fireball on March 29,2006] (full details: orbit, charts, spectra, composition) Retrieved 2008-07-07

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
* [ The Great Daylight 1972 Fireball] youtube link to Linda Baker's film

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