Meteor

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Meteor seen from the site of the Atacama Large Millimeter Array (ALMA) Cosmic Fireball Falling Over ALMA.jpg
Meteor seen from the site of the Atacama Large Millimeter Array (ALMA)

A meteor, known colloquially as a shooting star or falling star, is the visible passage of a glowing meteoroid, micrometeoroid, comet or asteroid through Earth's atmosphere, after being heated to incandescence by collisions with air molecules in the upper atmosphere, [2] [3] [4] 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, [5] meteors typically occur in the mesosphere at altitudes from 76 to 100 km (250,000 to 330,000 ft). [6] [7] The root word meteor comes from the Greek meteōros, meaning "high in the air". [3]

Contents

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. [8] Meteors may occur in showers, 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 30 km/s (67,000 mph), [9] the orbital speeds of meteoroids, and the gravity well of Earth.

Meteors become visible between about 75 to 120 km (250,000 to 390,000 ft) above Earth. They usually disintegrate at altitudes of 50 to 95 km (160,000 to 310,000 ft). [10] 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 10 cm (3.9 in) 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

Meteors were not known to be an astronomical phenomenon until early in the nineteenth century. Before 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 chemistry professor Benjamin Silliman investigated a meteorite that fell in Weston, Connecticut. [11] 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. [12] 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 called, moved with the stars, staying in the constellation Leo. [13]

The astronomer Denison Olmsted extensively studied this storm, concluding that it had a cosmic origin. After reviewing historical records, Heinrich Wilhelm Matthias Olbers predicted the storm's return in 1867, drawing other astronomers' attention to the phenomenon. Hubert A. Newton's more thorough historical work led to a refined prediction of 1866, which proved correct. [12] With Giovanni Schiaparelli's success in connecting the Leonids (as they are called) with comet Tempel-Tuttle, the cosmic origin of meteors was firmly established. Still, they remain an atmospheric phenomenon and retain their name "meteor" from the Greek word for "atmospheric". [14]

Fireball

Footage of a superbolide, a very bright fireball that exploded over Chelyabinsk Oblast, Russia in 2013

A fireball is a brighter-than-usual meteor that also becomes visible when about 100 km from sea level. The International Astronomical Union (IAU) defines a fireball as "a meteor brighter than any of the planets" (apparent magnitude −4 or greater). [15] 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. 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. [16]

Fireballs reaching apparent magnitude −14 or brighter are called bolides. [17] 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. [18] 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). [19] The word bolide comes from the Greek βολίς (bolis) [20] which can mean a missile or to flash. If the magnitude of a bolide reaches −17 or brighter it is known as a superbolide. [17] [21] 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 every year. [22] There are probably more than 500,000 fireballs a year, [23] 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. [24]

Fireball Sightings reported to the American Meteor Society  [22]
Year20082009201020112012201320142015201620172018201920202021
Number7346769531,6602,1833,5993,7894,2505,3915,5105,9936,9788,2599,629

Effect on atmosphere

A meteoroid of the Perseids with a size of about ten millimetres entering the earth's atmosphere in real time. The meteoroid is at the bright head of the trail, and the ionisation of the mesosphere is still visible in the tail. P10220XX.01.49.MESZ.14.08.2019.Berlin.Perseiden.x1.0.gif
A meteoroid of the Perseids with a size of about ten millimetres entering the earth's atmosphere in real time. The meteoroid is at the bright head of the trail, and the ionisation of the mesosphere is still visible in the tail.

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, 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. [25] Meteoroids or their fragments achieve dark flight after deceleration to terminal velocity. [26] Dark flight starts when they decelerate to about 2–4 km/s (4,500–8,900 mph). [27] Larger fragments fall further down the strewn field.

Colours

A meteor of the Leonid meteor shower; the photograph shows the meteor, afterglow, and wake as distinct components Leonid Meteor.jpg
A meteor of the Leonid meteor shower; the photograph shows the meteor, afterglow, and wake as distinct components

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: [28]

Acoustic manifestations

The 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 of 2001, "crackling", "swishing", or "hissing" sounds have been reported, [29] occurring at the same instant as a meteor flare. These are sometimes called electrophonic sounds. [30] Similar sounds have also been reported during intense displays of Earth's auroras. [31] [32] [33] [34]

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, generating pulses of radio waves. As the trail dissipates, megawatts of electromagnetic power could be released, with a peak in the power spectrum at audio frequencies. Physical vibrations 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. [35] [36] [37] [38] This proposed mechanism, although proven 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. [39] (Also see Bolide.)

Meteor shower

Multiple meteors photographed over an extended exposure time during a meteor shower Meteor burst.jpg
Multiple meteors photographed over an extended exposure time during a meteor shower
Meteor shower on chart PSM V18 D201 Shower of perseids sept 6 and 7.jpg
Meteor shower on chart

A meteor shower is the result of an interaction between a planet, such as Earth, and streams of debris from a comet 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, [40] and by breakup. Each time a comet swings by the Sun in its orbit, 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 sightings increases by about 10–30% during the weeks of vernal equinox. [41] Even meteorite 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. [42] 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. [43]

Notable meteors

Comparison of approximate sizes of notable impactors with the Hoba meteorite, a Boeing 747 and a New Routemaster bus Meteoroid size comparison.svg
Comparison of approximate sizes of notable impactors with the Hoba meteorite, a Boeing 747 and a New Routemaster bus
1992 –Peekskill, New York
The Peekskill Meteorite was recorded on October 9, 1992 by at least 16 independent videographers. [44] 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 430 to 500 mi (700 to 800 km). [45] One meteorite recovered at Peekskill, New York, for which the event and object gained their name, had a mass of 27 lb (12.4 kg) and was subsequently identified as an H6 monomict breccia meteorite. [46] 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.
2009 –Bone, Indonesia
A large fireball was observed in the skies near Bone, Sulawesi, Indonesia on October 8, 2009. This was thought to be caused by an asteroid approximately 10 m (33 ft) in diameter. The fireball contained an estimated energy of 50 kilotons of TNT, or about twice the Nagasaki atomic bomb. No injuries were reported. [47]
2009 –Southwestern 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 (9,610 ft (2,930 m) above sea level) recorded a movie of the passage of the object to the north. [48] [49] It had a spherical "ghost" image slightly trailing the main object (likely a lens reflection of the intense fireball), and a bright fireball explosion associated with the breakup of a substantial fraction of the object. An object trail continued northward after the fireball. The shock from the final breakup triggered seven seismological stations in northern Utah. The seismic data yielded a terminal location of the object at 40.286 N, −113.191 W, altitude 90,000 ft (27 km).[ citation needed ] This is above the Dugway Proving Grounds, a closed Army testing base.
2013 –Chelyabinsk Oblast, Russia
The Chelyabinsk meteor was an extremely bright, exploding fireball, or superbolide, measuring about 17 to 20 m (56 to 66 ft) across, with an estimated mass of 11,000 tonnes as the relatively small asteroid entered Earth's atmosphere. [50] [51] It was the largest natural object known 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 25 to 30 km (80,000 to 100,000 ft) 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 one minute and up to at least three 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. [52]
2019 –Midwestern 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 meteor was part of the South Taurids meteor shower. [53] It traveled east to west ending its flight somewhere near Wellsville, Missouri. [54] [55]

Monitoring

World map of large meteoric events (also see Fireball below) SmallAsteroidImpacts-Frequency-Bolide-20141114.jpg
World map of large meteoric events (also see Fireball below) 

In a range of countries networks of sky observing installations have been set up to monitor meteors.

See also

Related Research Articles

<span class="mw-page-title-main">Leonids</span> Meteor shower associated with the comet Tempel–Tuttle

The Leonids are a prolific annual meteor shower associated with the comet Tempel–Tuttle, and 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 in the constellation Leo: the meteors appear to radiate from that point in the sky. Their proper Greek name should be Leontids with an additional ⟨t⟩, but the word was initially constructed as a Greek/Latin hybrid and it has been used since.

<span class="mw-page-title-main">Tunguska event</span> 1908 meteor air burst explosion in Siberia

The Tunguska event was a large explosion of between 3 and 50 megatons that occurred near the Podkamennaya Tunguska River in Yeniseysk Governorate, Russia, on the morning of 30 June 1908. The explosion over the sparsely populated East Siberian taiga flattened an estimated 80 million trees over an area of 2,150 km2 (830 sq mi) of forest, and eyewitness accounts suggest up to three people may have died. The explosion is generally attributed to a meteor air burst, the atmospheric explosion of a stony asteroid about 50–60 metres wide. The asteroid approached from the east-south-east, probably with a relatively high speed of about 27 km/s (60,000 mph). Though the incident is classified as an impact event, the object is thought to have exploded at an altitude of 5 to 10 kilometres rather than hitting the Earth's surface, leaving no impact crater.

<span class="mw-page-title-main">Meteoroid</span> Sand- to boulder-sized particle of debris in the Solar System

A meteoroid is a small rocky or metallic body in outer space. Meteoroids are distinguished as objects significantly smaller than asteroids, ranging in size from grains to objects up to a meter wide. Objects smaller than meteoroids are classified as micrometeoroids or space dust. Many are fragments from comets or asteroids, whereas others are collision impact debris ejected from bodies such as the Moon or Mars.

<span class="mw-page-title-main">Meteor shower</span> Celestial event caused by streams of meteoroids entering Earths atmosphere

A meteor shower is a celestial event in which a number of meteors are observed to radiate, or originate, from one point in the night sky. These meteors are caused by streams of cosmic debris called meteoroids entering Earth's atmosphere at extremely high speeds on parallel trajectories. Most meteors are smaller than a grain of sand, so almost all of them disintegrate and never hit the Earth's surface. Very intense or unusual meteor showers are known as meteor outbursts and meteor storms, which produce at least 1,000 meteors an hour, most notably from the Leonids. The Meteor Data Centre lists over 900 suspected meteor showers of which about 100 are well established. Several organizations point to viewing opportunities on the Internet. NASA maintains a daily map of active meteor showers.

<span class="mw-page-title-main">Perseids</span> Prolific meteor shower associated with the comet Swift-Tuttle

The Perseids are a prolific meteor shower associated with the comet Swift–Tuttle that are usually visible from mid-July to late-August. The meteors are called the Perseids because they appear from the general direction of the constellation Perseus and in more modern times have a radiant bordering on Cassiopeia and Camelopardalis.

<span class="mw-page-title-main">Bolide</span> Extremely bright meteor

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 synonym for a fireball, sometimes specific to those with an apparent magnitude of −4 or brighter.

<span class="mw-page-title-main">Sikhote-Alin meteorite</span> 1947 meteorite impact in southeastern Russia

In southeastern Russia, an iron meteorite fell on the Sikhote-Alin Mountains in 1947. Large iron meteorite falls have been witnessed, and fragments have been recovered, but never before in recorded history has a fall of this magnitude occurred. An estimated 23 tonnes of fragments survived the fiery passage through the atmosphere and reached the Earth.

<span class="mw-page-title-main">Modra Observatory</span> Observatory

The Astronomical Observatory of Modra, also known as Modra Observatory or the Astronomical and Geophysical observatory in Modra, is an astronomical observatory located in Modra, Slovakia. It is owned and operated by the Comenius University in Bratislava. The scientific research at the observatory is led by the Department of Astronomy, Physics of the Earth and Meteorology, Faculty of Mathematics, Physics and Informatics.

The Taurids are an annual meteor shower, associated with the comet Encke. The Taurids are actually two separate showers, with a Southern and a Northern component. The Southern Taurids originated from Comet Encke, while the Northern Taurids originated from the asteroid 2004 TG10, possibly a large fragment of Encke due to its similar orbital parameters. They are named after their radiant point in the constellation Taurus, where they are seen to come from in the sky. Because of their occurrence in late October and early November, they are also called Halloween fireballs. Since 2P/Encke is such a short period comet, the meteors have the slowest impact speed of the annual well-known meteor showers.

<span class="mw-page-title-main">Radiant (meteor shower)</span> Celestial point in the sky from which meteors appear to originate

The radiant or apparent radiant of a meteor shower is the celestial point in the sky from which the paths of meteors appear to originate. The Perseids, for example, are meteors which appear to come from a point within the constellation of Perseus.

<span class="mw-page-title-main">Peter Jenniskens</span> Dutch astronomer

Petrus Matheus Marie (Peter) Jenniskens is a Dutch-American astronomer and a senior research scientist at the Carl Sagan Center of the SETI Institute and at NASA Ames Research Center. He is an expert on meteor showers, and wrote the book Meteor Showers and their Parent Comets, published in 2006 and Atlas of Earth’s Meteor Showers, published in 2023. He is past president of Commission 22 of the International Astronomical Union (2012–2015) and was chair of the Working Group on Meteor Shower Nomenclature (2006–2012) after it was first established. Asteroid 42981 Jenniskens is named in his honor.

The Great Daylight Fireball was an Earth-grazing fireball that passed within 57 kilometres of Earth's surface at 20:29 UTC on August 10, 1972. It entered Earth's atmosphere at a speed of 15 kilometres per second (9.3 mi/s) in daylight over Utah, United States and passed northwards leaving the atmosphere over Alberta, Canada. It was seen by many people and recorded on film and by space-borne sensors. An eyewitness to the event, located in Missoula, Montana, saw the object pass directly overhead and heard a double sonic boom. The smoke trail lingered in the atmosphere for several minutes.

<span class="mw-page-title-main">Meteor air burst</span> Atmospheric explosion of a meteor

A meteor air burst is a type of air burst in which a meteoroid explodes after entering a planetary body's atmosphere. This fate leads them to be called fireballs or bolides, with the brightest air bursts known as superbolides. Such meteoroids were originally asteroids and comets of a few to several tens of meters in diameter. This separates them from the much smaller and far more common "shooting stars", that usually burn up quickly upon atmospheric entry.

<span class="mw-page-title-main">Meteor procession</span> Meteor that breaks apart into fragments travelling in the same direction

A meteor procession occurs when an Earth-grazing meteor breaks apart, and the fragments travel across the sky in the same path. According to physicist Donald Olson, only four occurrences are known:

<span class="mw-page-title-main">Earth-grazing fireball</span> Meteoroid that enters Earths atmosphere and leaves again

An Earth-grazing fireball is a fireball, a very bright meteor that enters Earth’s atmosphere and leaves again. Some fragments may impact Earth as meteorites, if the meteor starts to break up or explodes in mid-air. These phenomena are then called Earth-grazing meteor processions and bolides. Famous examples of Earth-grazers are the 1972 Great Daylight Fireball and the Meteor Procession of July 20, 1860.

<span class="mw-page-title-main">Sutter's Mill meteorite</span> Meteorite that fell to Earth on 22 April 2012

The Sutter's Mill meteorite is a carbonaceous chondrite which entered the Earth's atmosphere and broke up at about 07:51 Pacific Time on April 22, 2012, with fragments landing in the United States. The name comes from Sutter's Mill, a California Gold Rush site, near which some pieces were recovered. Meteor astronomer Peter Jenniskens assigned Sutter's Mill (SM) numbers to each meteorite, with the documented find location preserving information about where a given meteorite was located in the impacting meteoroid. As of May 2014, 79 fragments had been publicly documented with a find location. The largest (SM53) weighs 205 grams (7.2 oz), and the second largest (SM50) weighs 42 grams (1.5 oz).

<span class="mw-page-title-main">Chelyabinsk meteor</span> Near-Earth asteroid that fell over Russia in 2013

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. It was caused by an approximately 18 m (60 ft) diameter, 9,100-tonne (10,000-short-ton) near-Earth asteroid that entered the atmosphere at a shallow 18‐degree angle with a speed relative to Earth of 19 kilometres per second. The light from the meteor was briefly brighter than the Sun, visible as far as 100 km (60 mi) away. It was observed in a wide area of the region and in neighbouring republics. Some eyewitnesses also reported feeling intense heat from the fireball.

<span class="mw-page-title-main">Earth-grazing meteoroid of 13 October 1990</span> Fireball meteoroid observed above Czechoslovakia and Poland

On 13 October 1990, meteoroid EN131090, with an estimated mass of 44 kg, entered the Earth's atmosphere above Czechoslovakia and Poland and, after a few seconds, returned to space. Observations of such events are quite rare; this was the second recorded using scientific astronomical instruments and the first recorded from two distant positions, which enabled the calculation of several of its orbital characteristics. The encounter with Earth significantly changed its orbit and, to a smaller extent, some of its physical properties.

References

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