The Great Daylight 1972 Fireball
Encyclopedia
The Great Daylight 1972 Fireball (or US19720810) was an Earth-grazing
meteoroid
which passed within 57 kilometres (35.4 mi) 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.
about 3 metres (9.8 ft) in diameter, if a carbonaceous chondrite
, to 14 metres (45.9 ft), if made of comet
ary ices. It 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-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).
The meteoroid's 100-second passage through the atmosphere reduced its velocity by about 800 m/s and the whole encounter significantly changed its orbital inclination from 15 degrees to 8 degrees.
The US19720810 meteoroid is described in the preface of the first chapter of Arthur C. Clarke
's The Hammer of God
.
. 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 by Collins et al. This table shows how sensitive the result is to the entry angle and composition:
Earth-grazing fireball
An Earth-grazing fireball is a small solar system body that enters the Earth's atmosphere and leaves again. If it starts to break up in the atmosphere it can become an Earth-grazing meteor procession, and some fragments may impact the Earth...
meteoroid
Meteoroid
A meteoroid is a sand- to boulder-sized particle of debris in the Solar System. The visible path of a meteoroid that enters Earth's atmosphere is called a meteor, or colloquially a shooting star or falling star. If a meteoroid reaches the ground and survives impact, then it is called a meteorite...
which passed within 57 kilometres (35.4 mi) of the surface of the Earth at 20:29 UTC on August 10, 1972. It entered the Earth's atmosphere in daylight over Utah
Utah
Utah is a state in the Western United States. It was the 45th state to join the Union, on January 4, 1896. Approximately 80% of Utah's 2,763,885 people live along the Wasatch Front, centering on Salt Lake City. This leaves vast expanses of the state nearly uninhabited, making the population the...
, United States (14:30 local time) and passed northwards leaving the atmosphere over Alberta
Alberta
Alberta is a province of Canada. It had an estimated population of 3.7 million in 2010 making it the most populous of Canada's three prairie provinces...
, Canada. It was seen by many people and recorded on film and by space-borne sensors.
Description
Analysis of its appearance and trajectory showed it was a meteoroidMeteoroid
A meteoroid is a sand- to boulder-sized particle of debris in the Solar System. The visible path of a meteoroid that enters Earth's atmosphere is called a meteor, or colloquially a shooting star or falling star. If a meteoroid reaches the ground and survives impact, then it is called a meteorite...
about 3 metres (9.8 ft) in diameter, if a carbonaceous chondrite
Carbonaceous chondrite
Carbonaceous chondrites or C chondrites are a class of chondritic meteorites comprising at least 7 known groups and many ungrouped meteorites. They include some of the most primitive known meteorites...
, to 14 metres (45.9 ft), if made of comet
Comet
A comet is an icy small Solar System body that, when close enough to the Sun, displays a visible coma and sometimes also a tail. These phenomena are both due to the effects of solar radiation and the solar wind upon the nucleus of the comet...
ary ices. It was in the Apollo asteroid
Apollo asteroid
The Apollo asteroids are a group of near-Earth asteroids named after 1862 Apollo, the first asteroid of this group to be discovered by Karl Wilhelm Reinmuth...
class in an Earth-crossing orbit
Earth-crosser asteroid
An Earth-crosser is a near-Earth asteroid whose orbit crosses that of Earth as observed from the ecliptic pole of Earth's orbit. The known numbered Earth-crossers are listed here. Those Earth-crossers whose semi-major axes are smaller than Earth's are Aten asteroids; the remaining ones are Apollo...
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).
The meteoroid's 100-second passage through the atmosphere reduced its velocity by about 800 m/s and the whole encounter significantly changed its orbital inclination from 15 degrees to 8 degrees.
The US19720810 meteoroid is described in the preface of the first chapter of Arthur C. Clarke
Arthur C. Clarke
Sir Arthur Charles Clarke, CBE, FRAS was a British science fiction author, inventor, and futurist, famous for his short stories and novels, among them 2001: A Space Odyssey, and as a host and commentator in the British television series Mysterious World. For many years, Robert A. Heinlein,...
's The Hammer of God
The Hammer of God
The Hammer of God is a science fiction novel by Arthur C. Clarke originally published in 1993. It deals with an asteroid named Kali headed toward Earth. Captain Robert Singh of the spacecraft Goliath is sent to deflect it. Kali is discovered by Dr...
.
What if it had collided?
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 velocityTerminal velocity
In fluid dynamics an object is moving at its terminal velocity if its speed is constant due to the restraining force exerted by the fluid through which it is moving....
. 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 by Collins et al. This table shows how sensitive the result is to the entry angle and composition:
| Diameter | Density | Entry angle | Energy lost | Airburst altitude | Airburst energy |
|---|---|---|---|---|---|
| 3 | 3.4 | 1 degree | 1.3 kiloton | 43 km | 0.7 kiloton |
| 3 | 3.4 | 45 degrees | 1.3 kiloton | 39 km | 0.4 kiloton |
| 8 | 0.9 | 1 degree | 6 kiloton | 80 km | 0.4 kiloton |
| 8 | 0.9 | 45 degrees | 6 kiloton | 45 km | 2 kiloton |
See also
- Earth-grazing fireballEarth-grazing fireballAn Earth-grazing fireball is a small solar system body that enters the Earth's atmosphere and leaves again. If it starts to break up in the atmosphere it can become an Earth-grazing meteor procession, and some fragments may impact the Earth...
- Meteor processionMeteor processionA meteor procession is the term used to describe when an Earth-grazing meteor breaks apart, and the fragments travel across the sky in the same path...
- Record-setting close approaches by asteroids to Earth
- 2008 TC32008 TC3thumb|right|300px|Ground path of the meteoroid; red line is the path, terminating where it would have hit the ground; green line is the infrasound detection of the explosion; orange crosshairs show METEOSAT IR fireball location; predicted altitudes are listed; exact path and fireball altitude not...
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