Earth-grazing fireball

An Earth-grazing fireball (or Earth-grazer)[2] is a small solar system body (SSSB) 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.[1] Famous examples of this are The Great Daylight 1972 Fireball and the Meteor Procession of July 20, 1860.[1][3][4]

As an Earth-grazer passes through the atmosphere its mass and velocity are changed, so that its orbit, when it re-enters space, might also change.[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, just incrementally thinner air from the stratosphere (~50 km), mesosphere, and (~85 km) 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). An SSSB 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)

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Known Earth-grazing fireballs

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. ^ a b c d http://www.txstate.edu/news/news_releases/news_archive/2010/06/YearOfMeteors060110.html
  2. ^ http://antwrp.gsfc.nasa.gov/apod/ap090302.html
  3. ^ a b Images of Harper's Weekly front page story
  4. ^ a b 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 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'
  7. ^ a b 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. ^ a b P. Spurný, J. Borovička, Z. Ceplecha and L. Shrbený, Astronomical Institute of the Academy of Sciences, 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
  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

Further reading

External links