Earth-grazing fireball
Encyclopedia
An Earth-grazing fireball (or Earth-grazer) 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. Famous examples of this are The Great Daylight 1972 Fireball
and the Meteor Procession of July 20, 1860.
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.
There is no exact criterion for passing by outside of the atmosphere, except perhaps roughly 80 km (49.7 mi) up, or the Kármán line
at 100 km (62.1 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
)
Small solar system body
A small Solar System body is an object in the Solar System that is neither a planet nor a dwarf planet, nor a satellite of a planet or dwarf planet:...
(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
Meteor procession
A 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...
, and some fragments may impact the Earth. Famous examples of this are The Great Daylight 1972 Fireball
The Great Daylight 1972 Fireball
The Great Daylight 1972 Fireball was an Earth-grazing meteoroid which passed within 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 and passed northwards leaving the atmosphere over Alberta, Canada...
and the Meteor Procession of July 20, 1860.
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.
There is no exact criterion for passing by outside of the atmosphere, except perhaps roughly 80 km (49.7 mi) up, or the Kármán line
Karman line
The Kármán line lies at an altitude of above the Earth's sea level, and is commonly used to define the boundary between the Earth's atmosphere and outer space...
at 100 km (62.1 mi). There is no agreed-upon end to the upper atmosphere, just incrementally thinner air from the stratosphere
Stratosphere
The stratosphere is the second major layer of Earth's atmosphere, just above the troposphere, and below the mesosphere. It is stratified in temperature, with warmer layers higher up and cooler layers farther down. This is in contrast to the troposphere near the Earth's surface, which is cooler...
(~50 km), mesosphere
Mesosphere
The mesosphere is the layer of the Earth's atmosphere that is directly above the stratosphere and directly below the thermosphere. In the mesosphere temperature decreases with increasing height. The upper boundary of the mesosphere is the mesopause, which can be the coldest naturally occurring...
, and (~85 km) thermosphere
Thermosphere
The thermosphere is the biggest of all the layers of the Earth's atmosphere directly above the mesosphere and directly below the exosphere. Within this layer, ultraviolet radiation causes ionization. The International Space Station has a stable orbit within the middle of the thermosphere, between...
(~690 km) up to the exosphere
Exosphere
The exosphere is the uppermost layer of Earth's atmosphere. In the exosphere, an upward travelling molecule moving fast enough to attain escape velocity can escape to space with a low chance of collisions; if it is moving below escape velocity it will be prevented from escaping from the celestial...
(~10,000) (See also thermopause
Thermopause
The thermopause is the atmospheric boundary of Earth's energy system, located at the top of the thermosphere.Below this, the atmosphere is defined to be active on the insolation received, due to the increased presence of heavier gases such as monoatomic oxygen. The solar constant is thus expressed...
.) For example, a 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...
can become a meteor
METEOR
METEOR is a metric for the evaluation of machine translation output. The metric is based on the harmonic mean of unigram precision and recall, with recall weighted higher than precision...
at an altitude of 85–120 km above the Earth.
The term Earth-grazer or inner-grazer
Inner-grazer
Inner-grazer is a class of solar orbits. This diagram shows the six possible types of orbits one planet can have in relation to another. The Sun is shown in the middle and the outer planet's orbital band is in yellow...
is also sometimes used for an asteroid
Asteroid
Asteroids are a class of small Solar System bodies in orbit around the Sun. They have also been called planetoids, especially the larger ones...
or 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...
whose orbit brings it close to Earth (such as within a Lunar distance
Lunar distance (astronomy)
In astronomy, a lunar distance is a measurement of the distance from the Earth to the Moon. The average distance from Earth to the Moon is 384,400 kilometers...
). An SSSB
Small solar system body
A small Solar System body is an object in the Solar System that is neither a planet nor a dwarf planet, nor a satellite of a planet or dwarf planet:...
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
Outer-grazer
Outer-grazer is a scheme of Sun Orbits, linked in with Inner-grazer. All six diagrams show the Sun in the middle and a putative planet's orbital band...
)
Known Earth-grazing fireballs
An Earth-grazing fireball is a rarely measured kind of fireball caused by a meteoroid that collides with the Earth but survives the collision by passing through, and exiting, the atmosphere. four grazers have been scientifically observed.- 1860-7-20, the Meteor Procession of July 20, 1860
- 1913-02-09, the Meteor Procession of February 9, 1913Meteor procession of February 9, 1913The meteor procession of February 9, 1913, was a unique meteoric phenomenon reported from locations across Canada, the north-eastern United States, Bermuda and from several ships at sea, including one off Brazil, giving a total recorded track of some 5659 miles...
led to conclusions a probable natural satelliteNatural satelliteA natural satellite or moon is a celestial body that orbits a planet or smaller body, which is called its primary. The two terms are used synonymously for non-artificial satellites of planets, of dwarf planets, and of minor planets....
of Earth had broken up - 1972-08-10, US19720810 at 15 km/s above United States and Canada (first scientific observation). (aka The Great Daylight 1972 Fireball)
- 1990-10-13, a 40 kilogram, 41.5 km per sec meteoroid passed at 97.9 km above Czechoslovakia
- 2006-03-29, fireball passed 18.8 km per sec through the atmosphere 71.4 km above Japan
- 2007-08-07, EN070807 passed through with an orbit belonging to the rare Aten asteroidAten asteroidThe Aten asteroids are a group of near-Earth asteroids, named after the first of the group to be discovered . They are defined by having semi-major axes of less than one astronomical unit...
type
See also
- MeteorMETEORMETEOR is a metric for the evaluation of machine translation output. The metric is based on the harmonic mean of unigram precision and recall, with recall weighted higher than precision...
- 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
- Near-earth asteroids
Further reading
External links
- Fireball of 1972
- Fireball of 1860 (painting)