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A meteoroid () is a small rocky or metallic body in
outer space Outer space, commonly shortened to space, is the expanse that exists beyond Earth and its atmosphere and between celestial bodies. Outer space is not completely empty—it is a near-perfect vacuum containing a low density of particles, pred ...
. Meteoroids are defined as objects significantly smaller than asteroids, ranging in size from grains to objects up to a meter wide. Objects smaller than this are classified as micrometeoroids or space dust. Most are fragments from
comet A comet is an icy, small Solar System body that, when passing close to the Sun, warms and begins to release gases, a process that is called outgassing. This produces a visible atmosphere or coma, and sometimes also a tail. These phenomena ...
s or asteroids, whereas others are collision impact debris ejected from bodies such as the
Moon The Moon is Earth's only natural satellite. It is the fifth largest satellite in the Solar System and the largest and most massive relative to its parent planet, with a diameter about one-quarter that of Earth (comparable to the width of ...
or
Mars Mars is the fourth planet from the Sun and the second-smallest planet in the Solar System, only being larger than Mercury. In the English language, Mars is named for the Roman god of war. Mars is a terrestrial planet with a thin at ...
. When a meteoroid, comet, or asteroid enters Earth's atmosphere at a speed typically in excess of , aerodynamic heating of that object produces a streak of light, both from the glowing object and the trail of glowing particles that it leaves in its wake. This phenomenon is called a
meteor A meteoroid () is a small rocky or metallic body in outer space. Meteoroids are defined as objects significantly smaller than asteroids, ranging in size from grains to objects up to a meter wide. Objects smaller than this are classified as mi ...
or "shooting star". Meteors typically become visible when they are about 100 km above sea level. A series of many meteors appearing seconds or minutes apart and appearing to originate from the same fixed point in the sky is called a meteor shower. A
meteorite A meteorite is a solid piece of debris from an object, such as a comet, asteroid, or meteoroid, that originates in outer space and survives its passage through the atmosphere to reach the surface of a planet or moon. When the original object ...
is the remains of a meteoroid that has survived the
ablation Ablation ( la, ablatio – removal) is removal or destruction of something from an object by vaporization, chipping, erosive processes or by other means. Examples of ablative materials are described below, and include spacecraft material for ...
of its surface material during its passage through the atmosphere as a meteor and has impacted the ground. An estimated 25 million meteoroids, micrometeoroids and other space debris enter Earth's atmosphere each day, which results in an estimated 15,000 tonnes of that material entering the atmosphere each year.


Meteoroids

In 1961, the
International Astronomical Union The International Astronomical Union (IAU; french: link=yes, Union astronomique internationale, UAI) is a nongovernmental organisation with the objective of advancing astronomy in all aspects, including promoting astronomical research, outreac ...
(IAU) defined a meteoroid as "a solid object moving in interplanetary space, of a size considerably smaller than an asteroid and considerably larger than an atom". In 1995, Beech and Steel, writing in the '' Quarterly Journal of the Royal Astronomical Society'', proposed a new definition where a meteoroid would be between 100
µm The micrometre ( international spelling as used by the International Bureau of Weights and Measures; SI symbol: μm) or micrometer ( American spelling), also commonly known as a micron, is a unit of length in the International System of Uni ...
and across. In 2010, following the discovery of asteroids below 10 m in size, Rubin and Grossman proposed a revision of the previous definition of meteoroid to objects between 10 µm and in diameter in order to maintain the distinction. According to Rubin and Grossman, the minimum size of an asteroid is given by what can be discovered from Earth-bound telescopes, so the distinction between meteoroid and asteroid is fuzzy. Some of the smallest asteroids discovered (based on
absolute magnitude Absolute magnitude () is a measure of the luminosity of a celestial object on an inverse logarithmic astronomical magnitude scale. An object's absolute magnitude is defined to be equal to the apparent magnitude that the object would have if it ...
''H'') are with ''H'' = 33.2 and with ''H'' = 32.1 both with an estimated size of . In April 2017, the IAU adopted an official revision of its definition, limiting size to between 30 µm and one meter in diameter, but allowing for a deviation for any object causing a meteor. Objects smaller than meteoroids are classified as
micrometeoroid A micrometeoroid is a tiny meteoroid: a small particle of rock in space, usually weighing less than a gram. A micrometeorite is such a particle that survives passage through Earth's atmosphere and reaches Earth's surface. The term "micrometeor ...
s and interplanetary dust. The
Minor Planet Center The Minor Planet Center (MPC) is the official body for observing and reporting on minor planets under the auspices of the International Astronomical Union (IAU). Founded in 1947, it operates at the Smithsonian Astrophysical Observatory. Function T ...
does not use the term "meteoroid".


Composition

Almost all meteoroids contain extraterrestrial nickel and iron. They have three main classifications: iron, stone, and stony-iron. Some stone meteoroids contain grain-like inclusions known as
chondrule A chondrule (from Ancient Greek χόνδρος ''chondros'', grain) is a round grain found in a chondrite. Chondrules form as molten or partially molten droplets in space before being accreted to their parent asteroids. Because chondrites repr ...
s and are called
chondrite A chondrite is a stony (non-metallic) meteorite that has not been modified, by either melting or differentiation of the parent body. They are formed when various types of dust and small grains in the early Solar System accreted to form pr ...
s. Stony meteoroids without these features are called " achondrites", which are typically formed from extraterrestrial igneous activity; they contain little or no extraterrestrial iron. The composition of meteoroids can be inferred as they pass through Earth's atmosphere from their trajectories and the light spectra of the resulting meteor. Their effects on radio signals also give information, especially useful for daytime meteors, which are otherwise very difficult to observe. From these trajectory measurements, meteoroids have been found to have many different orbits, some clustering in streams ''(see meteor showers)'' often associated with a parent
comet A comet is an icy, small Solar System body that, when passing close to the Sun, warms and begins to release gases, a process that is called outgassing. This produces a visible atmosphere or coma, and sometimes also a tail. These phenomena ...
, others apparently sporadic. Debris from meteoroid streams may eventually be scattered into other orbits. The light spectra, combined with trajectory and light curve measurements, have yielded various compositions and densities, ranging from fragile snowball-like objects with density about a quarter that of ice, to nickel-iron rich dense rocks. The study of meteorites also gives insights into the composition of non-ephemeral meteoroids.


In the Solar System

Most meteoroids come from the asteroid belt, having been perturbed by the gravitational influences of planets, but others are particles from
comet A comet is an icy, small Solar System body that, when passing close to the Sun, warms and begins to release gases, a process that is called outgassing. This produces a visible atmosphere or coma, and sometimes also a tail. These phenomena ...
s, giving rise to meteor showers. Some meteoroids are fragments from bodies such as Mars or our moon, that have been thrown into space by an impact. Meteoroids travel around the Sun in a variety of orbits and at various velocities. The fastest move at about through space in the vicinity of Earth's orbit. This is escape velocity from the Sun, equal to the square root of two times Earth's speed, and is the upper speed limit of objects in the vicinity of Earth, unless they come from interstellar space. Earth travels at about , so when meteoroids meet the atmosphere head-on (which only occurs when meteors are in a retrograde orbit such as the Eta Aquariids, which are associated with the retrograde Halley's Comet) the combined speed may reach about (see Specific energy#Astrodynamics). Meteoroids moving through Earth's orbital space average about . On January 17, 2013, at 05:21 PST, a one meter-sized comet from the Oort cloud entered Earth atmosphere over
California California is a state in the Western United States, located along the Pacific Coast. With nearly 39.2million residents across a total area of approximately , it is the most populous U.S. state and the 3rd largest by area. It is also the m ...
and
Nevada Nevada ( ; ) is a U.S. state, state in the Western United States, Western region of the United States. It is bordered by Oregon to the northwest, Idaho to the northeast, California to the west, Arizona to the southeast, and Utah to the east. N ...
. The object had a retrograde orbit with perihelion at 0.98 ± 0.03  AU. It approached from the direction of the constellation Virgo (which was in the south about 50° above the horizon at the time), and collided head-on with Earth's atmosphere at , vaporising more than above ground over a period of several seconds.


Collision with Earth's atmosphere

When meteoroids intersect with Earth's atmosphere at night, they are likely to become visible as meteors. If meteoroids survive the entry through the atmosphere and reach Earth's surface, they are called meteorites. Meteorites are transformed in structure and chemistry by the heat of entry and force of impact. A noted asteroid, , was observed in space on a collision course with Earth on 6 October 2008 and entered Earth's atmosphere the next day, striking a remote area of northern Sudan. It was the first time that a meteoroid had been observed in space and tracked prior to impacting Earth.
NASA The National Aeronautics and Space Administration (NASA ) is an independent agency of the US federal government responsible for the civil space program, aeronautics research, and space research. NASA was established in 1958, succeedin ...
has produced a map showing the most notable asteroid collisions with Earth and its atmosphere from 1994 to 2013 from data gathered by U.S. government sensors (see below).


Meteors

A meteor, known colloquially as a shooting star or falling star, is the visible passage of a glowing meteoroid,
micrometeoroid A micrometeoroid is a tiny meteoroid: a small particle of rock in space, usually weighing less than a gram. A micrometeorite is such a particle that survives passage through Earth's atmosphere and reaches Earth's surface. The term "micrometeor ...
,
comet A comet is an icy, small Solar System body that, when passing close to the Sun, warms and begins to release gases, a process that is called outgassing. This produces a visible atmosphere or coma, and sometimes also a tail. These phenomena ...
or asteroid through Earth's atmosphere, after being heated to incandescence by collisions with air molecules in the upper atmosphere, creating a streak of light via its rapid motion and sometimes also by shedding glowing material in its wake. Although a meteor may seem to be a few thousand feet from the Earth, meteors typically occur in the mesosphere at altitudes from . The root word ''meteor'' comes from the Greek ''meteōros'', meaning "high in the air". Millions of meteors occur in Earth's atmosphere daily. Most meteoroids that cause meteors are about the size of a grain of sand, i.e. they are usually millimeter-sized or smaller. Meteoroid sizes can be calculated from their mass and density which, in turn, can be estimated from the observed meteor trajectory in the upper atmosphere. Meteors may occur in
showers A shower is a place in which a person bathes under a spray of typically warm or hot water. Indoors, there is a drain in the floor. Most showers have temperature, spray pressure and adjustable showerhead nozzle. The simplest showers have a ...
, which arise when Earth passes through a stream of debris left by a comet, or as "random" or "sporadic" meteors, not associated with a specific stream of space debris. A number of specific meteors have been observed, largely by members of the public and largely by accident, but with enough detail that orbits of the meteoroids producing the meteors have been calculated. The atmospheric velocities of meteors result from the movement of Earth around the Sun at about , the orbital speeds of meteoroids, and the
gravity well The Hill sphere of an astronomical body is the region in which it dominates the attraction of satellites. To be retained by a planet, a moon must have an orbit that lies within the planet's Hill sphere. That moon would, in turn, have a Hil ...
of Earth. Meteors become visible between about above Earth. They usually disintegrate at altitudes of . Meteors have roughly a fifty percent chance of a daylight (or near daylight) collision with Earth. Most meteors are, however, observed at night, when darkness allows fainter objects to be recognized. For bodies with a size scale larger than to several meters meteor visibility is due to the atmospheric ram pressure (not friction) that heats the meteoroid so that it glows and creates a shining trail of gases and melted meteoroid particles. The gases include vaporised meteoroid material and atmospheric gases that heat up when the meteoroid passes through the atmosphere. Most meteors glow for about a second.


History

Although meteors have been known since ancient times, they were not known to be an astronomical phenomenon until early in the nineteenth century. Prior to that, they were seen in the West as an atmospheric phenomenon, like lightning, and were not connected with strange stories of rocks falling from the sky. In 1807,
Yale University Yale University is a private research university in New Haven, Connecticut. Established in 1701 as the Collegiate School, it is the third-oldest institution of higher education in the United States and among the most prestigious in the w ...
chemistry professor Benjamin Silliman investigated a meteorite that fell in Weston, Connecticut. Silliman believed the meteor had a cosmic origin, but meteors did not attract much attention from astronomers until the spectacular meteor storm of November 1833. People all across the eastern United States saw thousands of meteors, radiating from a single point in the sky. Careful observers noticed that the radiant, as the point is now called, moved with the stars, staying in the constellation Leo. The astronomer Denison Olmsted made an extensive study of this storm, and concluded that it had a cosmic origin. After reviewing historical records, Heinrich Wilhelm Matthias Olbers predicted the storm's return in 1867, which drew the attention of other astronomers to the phenomenon. Hubert A. Newton's more thorough historical work led to a refined prediction of 1866, which proved to be correct. With Giovanni Schiaparelli's success in connecting the
Leonids The Leonids ( ) are a prolific meteor shower associated with the comet Tempel–Tuttle, which are also known for their spectacular meteor storms that occur about every 33 years. The Leonids get their name from the location of their radiant ...
(as they are now called) with comet Tempel-Tuttle, the cosmic origin of meteors was now firmly established. Still, they remain an atmospheric phenomenon, and retain their name "meteor" from the Greek word for "atmospheric".


Fireball

A fireball is a brighter-than-usual meteor that also becomes visible when about 100 km from sea level. The
International Astronomical Union The International Astronomical Union (IAU; french: link=yes, Union astronomique internationale, UAI) is a nongovernmental organisation with the objective of advancing astronomy in all aspects, including promoting astronomical research, outreac ...
(IAU) defines a fireball as "a meteor brighter than any of the planets" (
apparent magnitude Apparent magnitude () is a measure of the brightness of a star or other astronomical object observed from Earth. An object's apparent magnitude depends on its intrinsic luminosity, its distance from Earth, and any extinction of the object's ...
−4 or greater). The International Meteor Organization (an amateur organization that studies meteors) has a more rigid definition. It defines a fireball as a meteor that would have a magnitude of −3 or brighter if seen at
zenith The zenith (, ) is an imaginary point directly "above" a particular location, on the celestial sphere. "Above" means in the vertical direction ( plumb line) opposite to the gravity direction at that location ( nadir). The zenith is the "high ...
. This definition corrects for the greater distance between an observer and a meteor near the horizon. For example, a meteor of magnitude −1 at 5 degrees above the horizon would be classified as a fireball because, if the observer had been directly below the meteor, it would have appeared as magnitude −6. Fireballs reaching apparent magnitude −14 or brighter are called bolides. The IAU has no official definition of "bolide", and generally considers the term synonymous with "fireball". Astronomers often use "bolide" to identify an exceptionally bright fireball, particularly one that explodes in a meteor air burst. They are sometimes called detonating fireballs. It may also be used to mean a fireball which creates audible sounds. In the late twentieth century, bolide has also come to mean any object that hits Earth and explodes, with no regard to its composition (asteroid or comet). The word ''bolide'' comes from the Greek βολίς (''bolis'') which can mean ''a missile'' or ''to flash''. If the magnitude of a bolide reaches −17 or brighter it is known as a
superbolide A bolide is normally taken to mean an exceptionally bright meteor, but the term is subject to more than one definition, according to context. It may refer to any large crater-forming body, or to one that explodes in the atmosphere. It can be a s ...
. A relatively small percentage of fireballs hit Earth's atmosphere and then pass out again: these are termed Earth-grazing fireballs. Such an event happened in broad daylight over North America in 1972. Another rare phenomenon is a meteor procession, where the meteor breaks up into several fireballs traveling nearly parallel to the surface of Earth. A steadily growing number of fireballs are recorded at the
American Meteor Society The American Meteor Society, Ltd. (AMS) is a non-profit scientific organization established to encourage and support the research activities of both amateur and professional astronomers who are interested in the field of meteor astronomy. Its aff ...
every year. There are probably more than 500,000 fireballs a year, but most go unnoticed because most occur over the ocean and half occur during daytime. A European Fireball Network and a NASA All-sky Fireball Network detect and track many fireballs.


Effect on atmosphere

The entry of meteoroids into Earth's atmosphere produces three main effects: ionization of atmospheric molecules, dust that the meteoroid sheds, and the sound of passage. During the entry of a meteoroid or asteroid into the
upper atmosphere Upper atmosphere is a collective term that refers to various layers of the atmosphere of the Earth above the troposphere and corresponding regions of the atmospheres of other planets, and includes: * The mesosphere, which on Earth lies between th ...
, an ionization trail is created, where the air molecules are ionized by the passage of the meteor. Such ionization trails can last up to 45 minutes at a time. Small, sand-grain sized meteoroids are entering the atmosphere constantly, essentially every few seconds in any given region of the atmosphere, and thus ionization trails can be found in the upper atmosphere more or less continuously. When radio waves are bounced off these trails, it is called meteor burst communications. Meteor radars can measure atmospheric density and winds by measuring the decay rate and Doppler shift of a meteor trail. Most meteoroids burn up when they enter the atmosphere. The left-over debris is called ''meteoric dust'' or just meteor dust. Meteor dust particles can persist in the atmosphere for up to several months. These particles might affect climate, both by scattering electromagnetic radiation and by catalyzing chemical reactions in the upper atmosphere. Meteoroids or their fragments achieve dark flight after deceleration to terminal velocity. Dark flight starts when they decelerate to about . Larger fragments fall further down the strewn field.


Colours

The visible light produced by a meteor may take on various hues, depending on the chemical composition of the meteoroid, and the speed of its movement through the atmosphere. As layers of the meteoroid abrade and ionize, the colour of the light emitted may change according to the layering of minerals. Colours of meteors depend on the relative influence of the metallic content of the meteoroid versus the superheated air plasma, which its passage engenders: * Orange-yellow (
sodium Sodium is a chemical element with the symbol Na (from Latin ''natrium'') and atomic number 11. It is a soft, silvery-white, highly reactive metal. Sodium is an alkali metal, being in group 1 of the periodic table. Its only stable ...
) * Yellow (
iron Iron () is a chemical element with symbol Fe (from la, ferrum) and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common element on Earth, right in ...
) * Blue-green (
magnesium Magnesium is a chemical element with the symbol Mg and atomic number 12. It is a shiny gray metal having a low density, low melting point and high chemical reactivity. Like the other alkaline earth metals (group 2 of the periodic ...
) * Violet (
calcium Calcium is a chemical element with the symbol Ca and atomic number 20. As an alkaline earth metal, calcium is a reactive metal that forms a dark oxide-nitride layer when exposed to air. Its physical and chemical properties are most similar ...
) * Red (atmospheric
nitrogen Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at se ...
and
oxygen Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements ...
)


Acoustic manifestations

Sound generated by a meteor in the upper atmosphere, such as a sonic boom, typically arrives many seconds after the visual light from a meteor disappears. Occasionally, as with the
Leonid meteor shower The Leonids ( ) are a prolific meteor shower associated with the comet Tempel–Tuttle, which are also known for their spectacular meteor storms that occur about every 33 years. The Leonids get their name from the location of their radiant i ...
of 2001, "crackling", "swishing", or "hissing" sounds have been reported, occurring at the same instant as a meteor flare. Similar sounds have also been reported during intense displays of Earth's auroras. Theories on the generation of these sounds may partially explain them. For example, scientists at NASA suggested that the turbulent ionized wake of a meteor interacts with
Earth's magnetic field Earth's magnetic field, also known as the geomagnetic field, is the magnetic field that extends from Earth's interior out into space, where it interacts with the solar wind, a stream of charged particles emanating from the Sun. The magneti ...
, generating pulses of
radio wave Radio waves are a type of electromagnetic radiation with the longest wavelengths in the electromagnetic spectrum, typically with frequencies of 300 gigahertz ( GHz) and below. At 300 GHz, the corresponding wavelength is 1 mm (sho ...
s. As the trail dissipates,
megawatt The watt (symbol: W) is the unit of power or radiant flux in the International System of Units (SI), equal to 1 joule per second or 1 kg⋅m2⋅s−3. It is used to quantify the rate of energy transfer. The watt is named after James ...
s of electromagnetic power could be released, with a peak in the power spectrum at audio frequencies. Physical
vibration Vibration is a mechanical phenomenon whereby oscillations occur about an equilibrium point. The word comes from Latin ''vibrationem'' ("shaking, brandishing"). The oscillations may be periodic, such as the motion of a pendulum—or random, su ...
s induced by the electromagnetic impulses would then be heard if they are powerful enough to make grasses, plants, eyeglass frames, the hearer's own body (see microwave auditory effect), and other conductive materials vibrate. This proposed mechanism, although proven to be plausible by laboratory work, remains unsupported by corresponding measurements in the field. Sound recordings made under controlled conditions in Mongolia in 1998 support the contention that the sounds are real. ''(Also see Bolide.)''


Meteor shower

A meteor shower is the result of an interaction between a planet, such as Earth, and streams of debris from a
comet A comet is an icy, small Solar System body that, when passing close to the Sun, warms and begins to release gases, a process that is called outgassing. This produces a visible atmosphere or coma, and sometimes also a tail. These phenomena ...
or other source. The passage of Earth through cosmic debris from comets and other sources is a recurring event in many cases. Comets can produce debris by water vapor drag, as demonstrated by Fred Whipple in 1951, and by breakup. Each time a comet swings by the Sun in its
orbit In celestial mechanics, an orbit is the curved trajectory of an object such as the trajectory of a planet around a star, or of a natural satellite around a planet, or of an artificial satellite around an object or position in space such as ...
, some of its ice vaporizes and a certain amount of meteoroids are shed. The meteoroids spread out along the entire orbit of the comet to form a meteoroid stream, also known as a "dust trail" (as opposed to a comet's "dust tail" caused by the very small particles that are quickly blown away by solar radiation pressure). The frequency of
fireball Fireball may refer to: Science * Fireball (meteor), a brighter-than-usual meteor * Ball lightning, an atmospheric electrical phenomenon * ''Bassia scoparia'', a plant species Arts and entertainment Films * '' The Fireball'', a 1950 film starring ...
sightings increases by about 10–30% during the weeks of vernal equinox. Even
meteorite A meteorite is a solid piece of debris from an object, such as a comet, asteroid, or meteoroid, that originates in outer space and survives its passage through the atmosphere to reach the surface of a planet or moon. When the original object ...
falls are more common during the northern hemisphere's spring season. Although this phenomenon has been known for quite some time, the reason behind the anomaly is not fully understood by scientists. Some researchers attribute this to an intrinsic variation in the meteoroid population along Earth's orbit, with a peak in big fireball-producing debris around spring and early summer. Others have pointed out that during this period the ecliptic is (in the northern hemisphere) high in the sky in the late afternoon and early evening. This means that fireball radiants with an asteroidal source are high in the sky (facilitating relatively high rates) at the moment the meteoroids "catch up" with Earth, coming from behind going in the same direction as Earth. This causes relatively low relative speeds and from this low entry speeds, which facilitates survival of meteorites. It also generates high fireball rates in the early evening, increasing chances of eyewitness reports. This explains a part, but perhaps not all of the seasonal variation. Research is in progress for mapping the orbits of the meteors to gain a better understanding of the phenomenon.


Notable meteors

; 1992Peekskill, New York : The Peekskill Meteorite was recorded on October 9, 1992 by at least 16 independent videographers. Eyewitness accounts indicate the fireball entry of the Peekskill meteorite started over West Virginia at 23:48 UT (±1 min). The fireball, which traveled in a northeasterly direction, had a pronounced greenish colour, and attained an estimated peak visual magnitude of −13. During a luminous flight time that exceeded 40 seconds the fireball covered a ground path of some . One meteorite recovered at Peekskill, New York, for which the event and object gained their name, had a mass of and was subsequently identified as an H6 monomict breccia meteorite. The video record suggests that the Peekskill meteorite had several companions over a wide area. The companions are unlikely to be recovered in the hilly, wooded terrain in the vicinity of Peekskill. ; 2009Bone, Indonesia : A large fireball was observed in the skies near
Bone A bone is a rigid organ that constitutes part of the skeleton in most vertebrate animals. Bones protect the various other organs of the body, produce red and white blood cells, store minerals, provide structure and support for the body, ...
,
Sulawesi Sulawesi (), also known as Celebes (), is an island in Indonesia. One of the four Greater Sunda Islands, and the world's eleventh-largest island, it is situated east of Borneo, west of the Maluku Islands, and south of Mindanao and the Sulu ...
, Indonesia on October 8, 2009. This was thought to be caused by an asteroid approximately in diameter. The fireball contained an estimated energy of 50 kilotons of TNT, or about twice the Nagasaki atomic bomb. No injuries were reported. ; 2009Southwestern US : A large bolide was reported on 18 November 2009 over southeastern California, northern Arizona, Utah, Wyoming, Idaho and Colorado. At 00:07 local time a security camera at the high altitude W. L. Eccles Observatory ( above sea level) recorded a movie of the passage of the object to the north. Of particular note in this video is the spherical "ghost" image slightly trailing the main object (this is likely a lens reflection of the intense fireball), and the bright fireball explosion associated with the breakup of a substantial fraction of the object. An object trail can be seen to continue northward after the bright fireball event. The shock from the final breakup triggered seven seismological stations in northern Utah; a timing fit to the seismic data yielded a terminal location of the object at 40.286 N, −113.191 W, altitude . This is above the Dugway Proving Grounds, a closed Army testing base. ; 2013Chelyabinsk Oblast, Russia : The
Chelyabinsk meteor The Chelyabinsk meteor was a superbolide that entered Earth's atmosphere over the southern Ural region in Russia on 15 February 2013 at about 09:20 YEKT (03:20 UTC). It was caused by an approximately near-Earth asteroid that entered the a ...
was an extremely bright, exploding
fireball Fireball may refer to: Science * Fireball (meteor), a brighter-than-usual meteor * Ball lightning, an atmospheric electrical phenomenon * ''Bassia scoparia'', a plant species Arts and entertainment Films * '' The Fireball'', a 1950 film starring ...
, known as
superbolide A bolide is normally taken to mean an exceptionally bright meteor, but the term is subject to more than one definition, according to context. It may refer to any large crater-forming body, or to one that explodes in the atmosphere. It can be a s ...
, measuring about across, with an estimated initial mass of 11,000 tonnes, as the relatively small asteroid entered Earth's atmosphere. It was the largest known natural object to have entered Earth's atmosphere since the Tunguska event in 1908. Over 1,500 people were injured mostly by glass from shattered windows caused by the air burst approximately above the environs of Chelyabinsk, Russia on 15 February 2013. An increasingly bright streak was observed during morning daylight with a large contrail lingering behind. At no less than 1 minute and up to at least 3 minutes after the object peaked in intensity (depending on distance from trail), a large concussive blast was heard that shattered windows and set-off car alarms, which was followed by a number of smaller explosions. ; 2019Midwestern United States : On November 11, 2019, a meteor was spotted streaking across the skies of the Midwestern United States. In the St. Louis Area, security cameras, dashcams, webcams, and video doorbells captured the object as it burned up in the earth's atmosphere. The
superbolide A bolide is normally taken to mean an exceptionally bright meteor, but the term is subject to more than one definition, according to context. It may refer to any large crater-forming body, or to one that explodes in the atmosphere. It can be a s ...
meteor was part of the South Taurids meteor shower. It traveled east to west ending its visible flight path somewhere over the US state of South Carolina becoming visible once again as it entered the earth's atmosphere creating a large fireball. The fireball was brighter than the planet Venus in the night sky.


Gallery of meteors

File:Orionid meteor.jpg, Orionid meteor File:Meteor Bolide.JPG, Sporadic bolide over the desert of Central Australia and a Lyrid (top edge) File:Looking Down on a Shooting Star.JPG, Meteor (center) seen from the
International Space Station The International Space Station (ISS) is the largest Modular design, modular space station currently in low Earth orbit. It is a multinational collaborative project involving five participating space agencies: NASA (United States), Roscosmos ( ...
File:Earth Sol63A UFO-A067R1.jpg, Possible meteor (center) photographed from Mars, March 7, 2004, by MER ''Spirit'' File:SL9ImpactGalileo.jpg, Comet Shoemaker–Levy 9 colliding with Jupiter: The sequence shows fragment W turning into a
fireball Fireball may refer to: Science * Fireball (meteor), a brighter-than-usual meteor * Ball lightning, an atmospheric electrical phenomenon * ''Bassia scoparia'', a plant species Arts and entertainment Films * '' The Fireball'', a 1950 film starring ...
on the planet's dark side


Meteorites

A meteorite is a portion of a meteoroid or asteroid that survives its passage through the atmosphere and hits the ground without being destroyed.''The Oxford Illustrated Dictionary''. 1976. Second Edition. Oxford University Press. p. 533 Meteorites are sometimes, but not always, found in association with hypervelocity impact craters; during energetic collisions, the entire impactor may be vaporized, leaving no meteorites.
Geologist A geologist is a scientist who studies the solid, liquid, and gaseous matter that constitutes Earth and other terrestrial planets, as well as the processes that shape them. Geologists usually study geology, earth science, or geophysics, althou ...
s use the term, "bolide", in a different sense from
astronomer An astronomer is a scientist in the field of astronomy who focuses their studies on a specific question or field outside the scope of Earth. They observe astronomical objects such as stars, planets, moons, comets and galaxies – in either ...
s to indicate a very large impactor. For example, the
USGS The United States Geological Survey (USGS), formerly simply known as the Geological Survey, is a scientific agency of the United States government. The scientists of the USGS study the landscape of the United States, its natural resources, ...
uses the term to mean a generic large crater-forming projectile in a manner "to imply that we do not know the precise nature of the impacting body ... whether it is a rocky or metallic asteroid, or an icy comet for example". Meteoroids also hit other bodies in the Solar System. On such stony bodies as the
Moon The Moon is Earth's only natural satellite. It is the fifth largest satellite in the Solar System and the largest and most massive relative to its parent planet, with a diameter about one-quarter that of Earth (comparable to the width of ...
or
Mars Mars is the fourth planet from the Sun and the second-smallest planet in the Solar System, only being larger than Mercury. In the English language, Mars is named for the Roman god of war. Mars is a terrestrial planet with a thin at ...
that have little or no atmosphere, they leave enduring craters.


Frequency of impacts

The diameter of the largest impactor to hit Earth on any given day is likely to be about , in a given year about , and in a given century about . These statistics are obtained by the following: Over at least the range from to roughly , the rate at which Earth receives meteors obeys a power-law distribution as follows: :N(>D) = 37 D^\ where ''N'' (>''D'') is the expected number of objects larger than a diameter of ''D'' meters to hit Earth in a year. This is based on observations of bright meteors seen from the ground and space, combined with surveys of
near-Earth asteroids A near-Earth object (NEO) is any small Solar System body whose orbit brings it into proximity with Earth. By convention, a Solar System body is a NEO if its closest approach to the Sun ( perihelion) is less than 1.3 astronomical units (AU ...
. Above in diameter, the predicted rate is somewhat higher, with a asteroid (one teraton TNT equivalent) every couple of million yearsabout 10 times as often as the power-law extrapolation would predict.


Impact craters

Meteoroid collisions with solid Solar System objects, including the Moon, Mercury, Callisto, Ganymede, and most small moons and asteroids, create impact craters, which are the dominant geographic features of many of those objects. On other planets and moons with active surface geological processes, such as Earth, Venus,
Mars Mars is the fourth planet from the Sun and the second-smallest planet in the Solar System, only being larger than Mercury. In the English language, Mars is named for the Roman god of war. Mars is a terrestrial planet with a thin at ...
,
Europa Europa may refer to: Places * Europe * Europa (Roman province), a province within the Diocese of Thrace * Europa (Seville Metro), Seville, Spain; a station on the Seville Metro * Europa City, Paris, France; a planned development * Europa Clif ...
, Io, and
Titan Titan most often refers to: * Titan (moon), the largest moon of Saturn * Titans, a race of deities in Greek mythology Titan or Titans may also refer to: Arts and entertainment Fictional entities Fictional locations * Titan in fiction, fictiona ...
, visible impact craters may become eroded, buried, or transformed by tectonics over time. In early literature, before the significance of impact cratering was widely recognised, the terms
cryptoexplosion In geology, a cryptoexplosion structure (or cryptovolcanic structure) is an explosion of unknown cause. The term is now largely obsolete. It was once commonly used to describe sites where there was geological evidence of a large-scale explosion wit ...
or cryptovolcanic structure were often used to describe what are now recognised as impact-related features on Earth. Molten terrestrial material ejected from a meteorite impact crater can cool and solidify into an object known as a tektite. These are often mistaken for meteorites.


Gallery of meteorites

File:Two tektites.JPG, Two tektites, molten terrestrial ejecta from a meteorite impact File:Esquel pallasite partial slice.jpg, A partial slice of the Esquel pallasite Image:Willamette Meteorite AMNH.jpg,
Willamette Meteorite The Willamette Meteorite, officially named WillametteMeteoritical Bulleti ...
, from Oregon, US Image:Meteorite Lapham.jpg, Meteorite, which fell in
Wisconsin Wisconsin () is a state in the upper Midwestern United States. Wisconsin is the 25th-largest state by total area and the 20th-most populous. It is bordered by Minnesota to the west, Iowa to the southwest, Illinois to the south, Lake M ...
in 1868 Image:Meteorito Marília.jpg, Marília Meteorite, a
chondrite A chondrite is a stony (non-metallic) meteorite that has not been modified, by either melting or differentiation of the parent body. They are formed when various types of dust and small grains in the early Solar System accreted to form pr ...
H4, which fell in Marília, Brazil (1971) File:Mesa-Arizona Museum of Natural History-Tucson Meteorite.JPG, Children posing behind the Tucson Meteorite at the Arizona Museum of Natural History File:Meteorite Tindouf NWA 869.jpg, Meteorite with
breccia Breccia () is a rock composed of large angular broken fragments of minerals or rocks cemented together by a fine-grained matrix. The word has its origins in the Italian language, in which it means "rubble". A breccia may have a variety of ...
tion and
carbon Carbon () is a chemical element with the symbol C and atomic number 6. It is nonmetallic and tetravalent—its atom making four electrons available to form covalent chemical bonds. It belongs to group 14 of the periodic table. Carbon ma ...
inclusions from Tindouf, Algeria


See also

*
Glossary of meteoritics This is a glossary of terms used in meteoritics, the science of meteorites. # * 2 Pallas – an asteroid from the asteroid belt and one of the likely parent bodies of the CR meteorites. * 4 Vesta – second-largest asteroid in the asteroid b ...


Relating to meteoroids

* Interplanetary dust *
Micrometeoroid A micrometeoroid is a tiny meteoroid: a small particle of rock in space, usually weighing less than a gram. A micrometeorite is such a particle that survives passage through Earth's atmosphere and reaches Earth's surface. The term "micrometeor ...
*
Near-Earth object A near-Earth object (NEO) is any small Solar System body whose orbit brings it into proximity with Earth. By convention, a Solar System body is a NEO if its closest approach to the Sun (Apsis, perihelion) is less than 1.3 astronomical unit ...


Relating to meteors

*
American Meteor Society The American Meteor Society, Ltd. (AMS) is a non-profit scientific organization established to encourage and support the research activities of both amateur and professional astronomers who are interested in the field of meteor astronomy. Its aff ...
* Bolide * Desert Fireball Network * Green fireballs * Hydrometeor * International Meteor Organization *
Leonids The Leonids ( ) are a prolific meteor shower associated with the comet Tempel–Tuttle, which are also known for their spectacular meteor storms that occur about every 33 years. The Leonids get their name from the location of their radiant ...
* List of meteor showers * Lyrids * Meteor air burst * North American Meteor Network * Orionids * Perseids * Tollmann's hypothetical bolide


Relating to meteorites

* Baetylus – Sacred stones made from meteorites * Impact crater * Impact event * *
Meteorite A meteorite is a solid piece of debris from an object, such as a comet, asteroid, or meteoroid, that originates in outer space and survives its passage through the atmosphere to reach the surface of a planet or moon. When the original object ...
* Micrometeorite * Tektite


References


External links


A History of Meteors and Other Atmospheric Phenomena

American Meteor Society

British Astronomical Society meteor page

International Meteor Organization



Meteoroids Page
a
NASA's Solar System Exploration

Meteor shower predictions

Meteor Showers and Viewing Tips

Society for Popular Astronomy – Meteor Section
* {{Authority control Articles containing video clips