View source for Meteoroid

{{Short description|Sand- to boulder-sized particle of debris in the Solar System}}
{{distinguish|Metroid|Matroid}}
[[File:Meteoroid meteor meteorite.gif|thumb|upright=1.5|A ''meteoroid'' shown entering the atmosphere, causing a visible ''[[meteor]]'' and hitting the Earth's surface, becoming a ''[[meteorite]]'']]

A '''meteoroid''' ({{IPAc-en|ˈ|m|iː|t|i|ə|r|ɔɪ|d}} {{respell|MEE|tee|ə|royd}})<ref>{{cite encyclopedia |url=https://dictionary.cambridge.org/dictionary/english/meteoroid |title=meteoroid |encyclopedia=[[Cambridge English Dictionary]]}}</ref> is a small body in [[outer space]].
Meteoroids are distinguished as objects significantly smaller than ''[[asteroid]]s'', ranging in size from grains to objects up to {{convert|1|m|ft|2|abbr=off|sp=us|spell=in}} wide.<ref name="Rubin2010"/> Objects smaller than meteoroids are classified as ''[[micrometeoroids]]'' or ''[[space dust]]''.<ref name="Rubin2010"/><ref>{{cite news |url=https://www.universetoday.com/36398/what-is-the-difference-between-asteroids-and-meteorites/ |title=What is the difference between asteroids and meteorites |first=Nancy |last=Atkinson |date=2 June 2015 |work=Universe Today}}</ref><ref>{{cite web |url=https://www.thefreedictionary.com/meteoroid |publisher=The Free Dictionary |title=meteoroids |access-date=1 August 2015}}</ref> Many are fragments from [[comet]]s or asteroids, whereas others are [[impact event|collision impact]] [[space debris|debris]] ejected from bodies such as the [[Moon]] or [[Mars]].<ref>{{cite web |url=http://education.nationalgeographic.co.uk/encyclopedia/meteoroid/ |title=Meteoroid |work=National Geographic |access-date=24 August 2015 |archive-url=https://web.archive.org/web/20151007141358/https://education.nationalgeographic.co.uk/encyclopedia/meteoroid/ |archive-date=7 October 2015}}</ref><ref>{{cite web |url=http://solarsystem.nasa.gov/planets/profile.cfm?Object=Meteors&Display=OverviewLong |title=Meteors & Meteorites |work=NASA |access-date=1 August 2015 |archive-date=26 December 2003 |archive-url=https://web.archive.org/web/20031226135836/http://www.solarsystem.nasa.gov/planets/profile.cfm?Object=Meteors&Display=OverviewLong}}</ref><ref>{{cite web |url=http://www.nasa.gov/mission_pages/asteroids/overview/fastfacts.html |title=Asteroid Fast Facts |publisher=NASA |date=31 March 2014 |access-date=1 August 2015}}</ref>

The visible passage of a meteoroid, comet, or asteroid [[atmospheric entry|entering Earth's atmosphere]] is called a [[meteor]], and 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]].

An estimated 25 million meteoroids, micrometeoroids and other [[space debris]] enter Earth's atmosphere each day,<ref>{{cite news |last=Lidz |first=Franz |url=https://www.smithsonianmag.com/smithsonian-institution/oldest-material-smithsonian-institution-came-outer-space-180971017/ |title=The Oldest Material in the Smithsonian Institution Came From Outer Space |work=[[Smithsonian (magazine)|Smithsonian]] |date=2019-01-09 |access-date=2019-01-09}}</ref> which results in an estimated {{Convert|15000|t|ST|0|abbr=off|adj=off}} of that material entering the atmosphere each year.<ref>{{cite episode |first=Stuart |last=Gary |title=Survey finds not all meteors the same |series=ABC Science |network=ABC |air-date=2011-12-22 |url=https://www.abc.net.au/science/articles/2011/12/22/3396756.htm}}</ref>
A ''[[meteorite]]'' is the remains of a meteoroid that has survived the [[ablation]] of its surface material during its passage through the atmosphere as a meteor and has impacted the ground.

== Meteoroids ==
{{See also|Micrometeoroid}}
[[Image:Meteoroid track through aerogel from EURECA mission.jpg|thumb|Meteoroid embedded in [[aerogel]]; the meteoroid is 10&nbsp;[[μm]] in diameter and its track is 1.5 mm long]]
[[File:323213main Petersmeteorites 946-710.jpg|thumb|{{mpl|2008 TC|3}} [[#Meteoroids|meteorite]] fragments found on February 28, 2009, in the [[Nubian Desert]], [[Sudan]]]]

In 1961, the [[International Astronomical Union]] (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".<ref name="IMO-meteoroid"/><ref name="Millman1961"/> 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 and 10 meters across.<ref name="Steel1995" /> 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 one meter in diameter in order to maintain the distinction.<ref name="Rubin2010"/> 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#Solar System bodies (H)|absolute magnitude]] ''H'') are {{mp|2008 TS|26}} with ''H'' = 33.2<ref name="smallest-jpl"/> and {{mpl|2011 CQ|1}} with ''H'' = 32.1<ref>{{cite web |url=http://ssd.jpl.nasa.gov/sbdb.cgi?sstr=2011CQ1;cad=1#cad |title=JPL Small-Body Database Browser: (2011 CQ1) |type=2011-02-04 last obs}}</ref> both with an estimated size of one meter.<ref name="NASA-166"/> In April 2017, the IAU adopted an official revision of its definition, limiting size to between {{cvt|30|μm|in}} and one meter in diameter, but allowing for a deviation for any object causing a meteor.<ref>{{cite news |author=Vincent Perlerin |title=Definitions of terms in meteor astronomy (IAU) |date=September 26, 2017 |work=News |publisher=[[International Meteor Organization]] |url=https://www.imo.net/definitions-of-terms-in-meteor-astronomy-iau/ |access-date=2018-01-22}}</ref>

Objects smaller than meteoroids are classified as [[micrometeoroid]]s and [[interplanetary dust cloud|interplanetary dust]]. The [[Minor Planet Center]] 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]]s and are called [[chondrite]]s. Stony meteoroids without these features are called "[[achondrite]]s", which are typically formed from extraterrestrial igneous activity; they contain little or no extraterrestrial iron.<ref>{{cite web | last = Notkin | first = Geoffrey | title = Meteorite types and classification | work = Meteorwritings | publisher = Geology.com | url = https://geology.com/meteorites/meteorite-types-and-classification.shtml | access-date = 2014-03-02}}</ref> 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]], 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,<ref>{{cite journal |last=Povenmire |first=Harold |url=https://www.lpi.usra.edu/meetings/lpsc2000/pdf/1183.pdf |title=Physical Dynamics of the Upsilon Pegasid Fireball – European Network 190882A |journal=Lunar and Planetary Science Conference |page=1183 |bibcode=2000LPI....31.1183P |year=2000}}</ref> to nickel-iron rich dense rocks. The study of [[Meteorite#Meteorite types|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]]s, giving rise to [[meteor shower]]s. Some meteoroids are fragments from bodies such as Mars or the [[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 42 km/s 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 29.6 km/s, so when meteoroids meet the atmosphere head-on (which only occurs when meteors are in a [[retrograde orbit]] such as the [[Leonids]], which are associated with the retrograde comet [[55P/Tempel–Tuttle]]) the combined speed may reach about 71 km/s (see [[Specific energy#Astrodynamics]]). Meteoroids moving through Earth's orbital space average about 20 km/s,<ref>{{cite journal |author=Interagency Group (Space) Working Group on Orbital Debris |title=Report on Orbital Debris |date=February 1989 |website=NASA Technical Reports Server |page=1 |url=https://ntrs.nasa.gov/citations/19900003319 |hdl=2060/19900003319 |access-date=2023-05-31 |archive-date=2023-05-31 |archive-url=https://web.archive.org/web/20230531171611/https://ntrs.nasa.gov/citations/19900003319 |url-status=dead}}</ref> but due to Earth's gravity meteors such as the [[Phoenicids]] can make atmospheric entry at as slow as about 11&nbsp;km/s.

On January 17, 2013, at 05:21 PST, a one meter comet from the [[Oort cloud]] entered Earth atmosphere over [[California]] and [[Nevada]].<ref name="CAMS"/> The object had a retrograde orbit with perihelion at 0.98&nbsp;±&nbsp;0.03&nbsp;[[Astronomical unit|AU]]. It approached from the direction of the constellation [[Virgo (constellation)|Virgo]] (which was in the south about 50° above the horizon at the time), and collided head-on with Earth's atmosphere at 72 ± 6 km/s<ref name="CAMS">{{cite web |title=2013 January 17 Sierra Nevada fireball |publisher=[[SETI Institute]] |first=Peter |last=Jenniskens |author-link=Peter Jenniskens |url=http://cams.seti.org/index-archive3.html |access-date=2014-11-16}} | {{cite web |url=http://www.seti.org/seti-institute/news/earth-collides-with-comet |title=Earth Collides Head-On with Small Comet |publisher=[[SETI Institute]] |access-date=2013-01-25 |archive-date=2013-01-28 |archive-url=https://web.archive.org/web/20130128052127/http://www.seti.org/seti-institute/news/earth-collides-with-comet}}</ref> vaporising more than 100 km above ground over a period of several seconds.

=== Collision with Earth's atmosphere ===
{{main|Meteor}}
[[File:Meteoroid meteor meteorite.gif|Animated illustration of different phases as a meteoroid enters the Earth's atmosphere to become visible as a [[meteor]] and land as a [[meteorite]]|thumb|right]]

When meteoroids intersect with Earth's atmosphere at night, they are likely to become visible as [[#Meteors|meteors]]. If meteoroids survive the entry through the atmosphere and reach Earth's surface, they are called [[#Meteorites|meteorites]]. Meteorites are transformed in structure and chemistry by the heat of entry and force of impact. A noted {{convert|4|m|sp=us|adj=on|}} [[asteroid]], {{mpl|2008 TC|3}}, was observed in space on a collision course with Earth on 6&nbsp;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.<ref name="IMO-meteoroid"/> [[NASA]] 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.<ref>{{cite web |title=New Map Shows Frequency of Small Asteroid Impacts, Provides Clues on Larger Asteroid Population |url=https://www.jpl.nasa.gov/news/new-map-shows-frequency-of-small-asteroid-impacts-provides-clues-on-larger-asteroid-population/ |website=NASA Jet Propulsion Laboratory (JPL) |access-date=17 February 2025}}</ref>

== Meteorites ==
{{Main|Meteorite}}
[[File:Murnpeowie meteorite.jpg|thumb|Murnpeowie [[meteorite]], an [[iron meteorite]] with [[wikt:regmaglypt|regmaglypts]] resembling thumbprints (Australia, 1910)]]

A meteorite is a portion of a meteoroid or asteroid that survives its passage through the atmosphere and hits the ground without being destroyed.<ref>''The Oxford Illustrated Dictionary''. 1976. Second Edition. Oxford University Press. p. 533</ref> Meteorites are sometimes, but not always, found in association with hypervelocity [[impact crater]]s; during energetic collisions, the entire impactor may be vaporized, leaving no meteorites. [[Geologist]]s use the term, "bolide", in a different sense from [[astronomer]]s to indicate a very large [[impact event|impactor]]. For example, the [[United States Geological Survey|USGS]] 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".<ref>{{cite web |url=https://woodshole.er.usgs.gov/epubs/bolide/introduction.html |title=What is a Bolide? |publisher=woodshole.er.usgs.gov |access-date=2011-09-16}}</ref>

Meteoroids also hit other bodies in the Solar System. On such stony bodies as the [[Moon]] or [[Mars]] that have little or no atmosphere, they leave enduring craters.

=== Impact craters ===
{{Main|Impact crater}}

Meteoroid collisions with solid Solar System objects, including the Moon, [[mercury (planet)|Mercury]], [[Callisto (moon)|Callisto]], [[Ganymede (moon)|Ganymede]], and most small moons and [[asteroid]]s, 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]], [[Europa (moon)|Europa]], [[io (moon)|Io]], and [[Titan (moon)|Titan]], visible impact craters may become [[erosion|eroded]], buried, or transformed by [[tectonics]] over time. In early literature, before the significance of impact cratering was widely recognised, the terms [[cryptoexplosion]] or cryptovolcanic structure were often used to describe what are now recognised as impact-related features on Earth.<ref>{{cite web |last1=French |first1=Bevan M. |author-link=Traces of Catastrophe |year=1998 |url=http://www.lpi.usra.edu/publications/books/CB-954/CB-954.intro.html |title=Traces of Catastrophe: A Handbook of Shock-Metamorphic Effects in Terrestrial Meteorite Impact Structures |location=Washington, DC |publisher=[[Smithsonian Institution]] |page=97}}</ref> 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. Terrestrial rock, sometimes with pieces of the original meteorite, created or modified by an impact of a meteorite is called [[impactite]].

=== Gallery of meteorites ===

<gallery class="center" mode="packed" heights="140px">
File:Two tektites.JPG|Two [[tektite]]s, molten terrestrial ejecta from a [[meteorite impact]]
File:Esquel pallasite partial slice.jpg|A partial slice of the [[Esquel (meteorite)|Esquel pallasite]]
Image:Willamette Meteorite AMNH.jpg|[[Willamette Meteorite]], from Oregon, US
Image:Meteorite Lapham.jpg|Meteorite, which fell in [[Wisconsin]] in 1868
Image:Meteorito Marília.jpg|[[Marília (meteorite)|Marília Meteorite]], a [[chondrite]] H4, which fell in [[Marília]], Brazil (1971)
File:Mesa-Arizona Museum of Natural History-Tucson Meteorite.JPG|Children posing behind a replica of the [[Tucson Ring meteorite|Tucson Meteorite]] at the [[Arizona Museum of Natural History]]<ref>{{cite web |url=https://www.arizonamuseumofnaturalhistory.org/explore-the-museum/exhibitions/arizona-through-time |title=Arizona Through Time |website=[[Arizona Museum of Natural History]] |access-date=2024-09-03}}</ref>
File:Meteorite Tindouf NWA 869.jpg|Meteorite with [[breccia]]tion and [[carbon]] inclusions from [[Tindouf]], Algeria<ref>{{cite web|url=http://www.lpi.usra.edu/meteor/metbull.php?code=31890|title=Northwest Africa 869|publisher=The Meteoritical Society|work=Meteoritical Bulletin Database}}</ref>
</gallery>

== See also ==
* [[Glossary of meteoritics]]

=== Relating to meteoroids ===
{{Div col|colwidth=16em}}
* [[Interplanetary dust]]
* [[Micrometeoroid]]
* [[Near-Earth object]]
{{Div col end}}

=== Relating to meteorites ===
{{Div col|colwidth=16em}}
* [[Baetyl]] – Sacred stones possibly originating as meteorites
* [[Impact crater]]
* [[Impact event]]
* {{section link|Interplanetary dust cloud|Collecting interplanetary dust on Earth}}
* [[Meteorite]]
* [[Micrometeorite]]
* [[Tektite]]
{{Div col end}}

== References ==
<references>
<ref name="IMO-meteoroid">{{cite web |title=Glossary International Meteor Organization |publisher=[[International Meteor Organization]] (IMO) |url=https://www.imo.net/glossary#letterm |access-date=2011-09-16}}</ref>
<ref name="Millman1961">{{cite journal |last=Millman |first=Peter M. |title=A report on meteor terminology |journal=Journal of the Royal Astronomical Society of Canada |volume=55 |pages=265–267 |year=1961 |bibcode=1961JRASC..55..265M}}</ref>
<ref name="Steel1995">{{cite journal |last1=Beech |first1=Martin |last2=Steel |first2=Duncan |title=On the Definition of the Term Meteoroid |journal=Quarterly Journal of the Royal Astronomical Society |volume=36 |issue=3 |pages=281–284 |date=September 1995 |bibcode=1995QJRAS..36..281B}})</ref>
<ref name="Rubin2010">{{cite journal |last1=Rubin |first1=Alan E. |last2=Grossman |first2=Jeffrey N. |title=Meteorite and meteoroid: New comprehensive definitions |journal=Meteoritics & Planetary Science |volume=45 |issue=1 |pages=114–122 |date=January 2010 |bibcode=2010M&PS...45..114R |doi = 10.1111/j.1945-5100.2009.01009.x |s2cid=129972426}})</ref>
<ref name="smallest-jpl">{{cite web |title=JPL Small-Body Database Search Engine: H > 29 (mag) |publisher=JPL Solar System Dynamics |url = http://ssd.jpl.nasa.gov/sbdb_query.cgi?obj_group=all;obj_kind=all;obj_numbered=all;OBJ_field=0;ORB_field=0;c1_group=OBJ;c1_item=Ai;c1_op=%3E;c1_value=29;table_format=HTML;max_rows=100;format_option=comp;c_fields=AcBhBgBjBiBnBsCkCqAi;.cgifields=format_option;.cgifields=ast_orbit_class;.cgifields=table_format;.cgifields=obj_kind;.cgifields=obj_group;.cgifields=obj_numbered;.cgifields=com_orbit_class&query=1&c_sort=AiD |access-date=2013-01-28}}</ref>
<ref name="NASA-166">{{cite web |date=November 9, 2009 |title=Small Asteroid 2009 VA Whizzes By the Earth |publisher=NASA's Near Earth Object Program Office |first1=Donald K. |last1=Yeomans |first2=Paul |last2=Chodas |first3=Steve |last3=Chesley |url = https://cneos.jpl.nasa.gov/news/news166.html |archive-url = https://web.archive.org/web/20091112105500/http://neo.jpl.nasa.gov/news/news166.html |url-status = live |archive-date = November 12, 2009 |access-date=2013-01-28}}</ref>
</references> <!-- end of reflist-->

== External links ==
{{Commons|Meteor}}
{{Wikisource index|Meteoroids}}
{{Wiktionary|meteoroid|meteor}}
* {{usurped|1=[https://web.archive.org/web/20090304172046/http://www.fireballhistory.com/ A History of Meteors and Other Atmospheric Phenomena]}}
* [https://www.amsmeteors.org/ American Meteor Society]
* [https://www.britastro.org/meteor British Astronomical Society meteor page]
* [http://www.imo.net/ International Meteor Organization]
* [https://www.meteorscan.com/meteor-live.html Live Meteor Scanner]
* [https://web.archive.org/web/20151207045337/http://solarsystem.nasa.gov/planets/profile.cfm?Object=Meteors Meteoroids Page] at [http://solarsystem.nasa.gov/ NASA's Solar System Exploration]
* [http://astroclub.tau.ac.il/ephem/Meteors/ Meteor shower predictions] {{Webarchive|url=https://web.archive.org/web/20110703174608/http://astroclub.tau.ac.il/ephem/Meteors/ |date=2011-07-03 }}
* [http://stardate.org/nightsky/meteors/ Meteor Showers and Viewing Tips]
* [https://www.popastro.com/meteor/index.php Society for Popular Astronomy – Meteor Section]
* {{YouTube |id = Ar_h-zAccsY |title = Minor Planet Center: Asteroid Hazards, Part 2: ''The Challenge of Detection'' }} {{small|(min. 7:14)}}
*[https://impact.ese.ic.ac.uk/ImpactEarth/ImpactEffects/ Earth Impact Effects Program] Estimates crater size and other effects of a specified body colliding with Earth.

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