There is no agreed-upon end to the upper atmosphere, but rather incrementally thinner air from thestratosphere (11~50 km (7~31 mi)),mesosphere (~85 km or 53 mi), andthermosphere (~690 km or 430 mi) up to theexosphere (~10,000 km or 6,200 mi) (see alsothermopause). For example, ameteoroid can become ameteor at an altitude of 85–120 km (53–75 mi) above the Earth.
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[update] four grazers have been scientifically observed.[9]
1972 Great Daylight Fireball, August 10, 1972, US19720810 at 15 km/s above United States and Canada (first scientific observation). It was estimated to have lost about half its mass,[6] and 800 m/s of velocity during the encounter.[5]
March 29, 2006, fireball passed 18.8 km/s through the atmosphere 71.4 km above Japan[11][12]
August 7, 2007, EN070807 passed through the atmosphere over Europe with an orbit belonging to the rareAten asteroid type[8][13]
June 10, 2012, an Earth-grazing fireball from the Daytime ζ-Perseid shower passed over Spain, travelling 510 km in the atmosphere. It was the faintest Earth-grazing meteor reported in the scientific literature and the first one belonging to a meteor shower.[14]
December 24, 2014, a slow movingChristmas Eve fireball SPMN241214 passed over north Africa, Spain, and Portugal, travelling about 1,200 km in the atmosphere.[15]
July 7, 2017, theDesert Fireball Network observed a grazing fireball that traveled over 1300 km through the atmosphere above Western Australia and South Australia. The closest approach was about 58.5 km, and the initial mass is estimated to be a minimum of ~60 kg. The meteoroid came from anApollo-type orbit, and due to the close encounter with the Earth, it was sent onto a Jupiter-family comet-like orbit.[16]
^abDaylight 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'
^Although other grazers have been seen and, rarely, photographed, without specialised scientific observations their orbits cannot be determined. An example is theLeonid grazer over Hawaii on 2001-11-18 -Abe 2006 (PDF)
The dictionary definition ofEarth-grazing at Wiktionary
