Earth-grazing fireball

Frederic Edwin Church, "The Meteor of 1860". 150 years later in 2010 it was determined to be an Earth-grazing meteor procession.[1]

An Earth-grazing fireball (or Earth-grazer)[2] 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 and become a meteorite.[1] Famous examples of this are the 1972 Great Daylight Fireball and the Meteor Procession of July 20, 1860.[1][3][4]

Overview

As an Earth-grazer passes through the atmosphere its mass and velocity are changed, so that its orbit, as it re-enters space, will be different from its orbit as it encountered Earth's atmosphere.[5][6][7]

There is no exact criterion for passing by outside of the atmosphere, except perhaps roughly 80 km (50 mi) up, or the Kármán line at 100 km (62 mi). There is no agreed-upon end to the upper atmosphere, but rather incrementally thinner air from the stratosphere (~50 km), mesosphere (~85 km), and thermosphere (~690 km) up to the exosphere (~10,000) (see also thermopause). For example, a meteoroid can become a meteor at an altitude of 85–120 km above the Earth.

The term Earth-grazer or inner-grazer is also sometimes used for an asteroid or meteoroid whose orbit brings it close to Earth (such as within a Lunar distance).

A small Solar System body with a grazing orbit does not necessarily make contact with the Earth's atmosphere, although it may be more likely to collide with it (see List of Earth-crossing minor planets and Outer-grazer).

Known Earth-grazing fireballs

All-sky photo with the Earth-grazing meteoroid of 13 October 1990 (the light track across the picture going from the south to the north) taken at Červená hora (Czechoslovakia), one of the stations of the European Fireball Network. The bright track on the left is the Moon.

An Earth-grazing fireball is a rarely measured kind of fireball[8] 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.[9]

See also

References

  1. ↑ 1.0 1.1 1.2 1.3 "Texas State astronomers solve Walt Whitman meteor mystery : University News Service : Texas State University". Retrieved 2013-10-19.. Txstate.edu (2010-05-28). Retrieved on 2013-10-19.
  2. ↑ "APOD: 2009 March 2 - Earthgrazer: The Great Daylight Fireball of 1972". Retrieved 2013-10-19.. Antwrp.gsfc.nasa.gov. Retrieved on 2013-10-19.
  3. ↑ 3.0 3.1 Images of Harper's Weekly front page story
  4. ↑ 4.0 4.1 150-year-old meteor mystery solved
  5. ↑ US19720810 (Daylight Earth grazer) Global Superbolic Network Archive, 2000, 'Size: 5 to 10 m'
  6. ↑ 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'
  7. ↑ 7.0 7.1 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)
  8. ↑ 8.0 8.1 Spurný, P. Spurný; J. Borovička, Z. Ceplecha and L. Shrbený (2008). "Precise Multi-instrument Data on 45 Fireballs Recorded over Central Europe in the Period 2006-2008" (PDF). Asteroids, Comets, Meteors (2008) (Czech Republic: Astronomical Institute of the Academy of Sciences, Fričova 298, CZ-251 65 Ondřejov Observatory). Retrieved 2008-07-06. EN070807 fireball ... very rare Earth-grazing fireball ... Aten type
  9. ↑ 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)
  10. ↑ 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
  11. ↑ Abe 2006 (abstract)
  12. ↑ Abe 2006 (PDF) approximately 100 kg, orbit aphelion reaches Jupiter
  13. ↑ EN indicates the European Fireball Network

External links