# Meteoroid <!-- SOLSIM:BEGIN g31 — Solar System explorer state (hand-built on wt-core, specs/solar/); do not hand-edit inside --> **Microsim — three.js (Wikitube framework):** *Interplanetary dust in the Solar System explorer* <div class="wt-sim" data-src="https://wikitube-3d-microsims.netlify.app/solar/Solar_System.html?obj=dust&embed=1" data-title="Interplanetary dust in the Solar System explorer"></div> *The Solar System explorer locked on this article's state (`?obj=dust`); every object and population of the [[PORTAL_Solar_System|Solar System portal]] has its own state in the same scene.* <!-- SOLSIM:END --> *Try: drag to an edge-on view and see the zodiacal dust points crowd toward the plane the planets share; press o to hide the orbit lines and pick out the Encke stream by its points alone; then set the speed to 1 month/s and watch Earth sweep past that stream once in each circuit, the encounter that produces the Southern Taurids.* A **meteoroid** is a small rocky or metallic body travelling through interplanetary space, larger than a dust grain and smaller than an [[Asteroid|asteroid]]. Under the definition the International Astronomical Union adopted in 2017, the class runs from about 30 micrometres to 1 metre across.[^imo2017] Most meteoroids are fragments shed by [[Comet|comets]] or broken from asteroids, and a few are rock blasted off the [[Moon]] or [[Mars]] by impacts.[^nasa-meteors][^rubin2010] When a meteoroid strikes the [[Atmosphere_of_Earth|atmosphere of Earth]], the glowing trail it makes is a meteor; many meteors that seem to fan out from one point of the sky over a night make a [[Meteor_shower|meteor shower]]. Any piece that survives the fall and reaches the ground is a meteorite. The traffic is heavy: an estimated 25 million meteoroids, micrometeoroids and other particles enter the atmosphere each day, delivering around 15,000 tonnes of material a year.[^lidz2019][^abc2011] This article covers how the class was defined, what meteoroids are made of, how fast they travel and how often [[Earth]] is hit, and what reaches the ground. The explorer at the top of this page shows the [[Interplanetary_dust_cloud|interplanetary dust cloud]] that fills the inner [[PORTAL_Solar_System|Solar System]], with the meteoroid stream strung along the orbit of Comet Encke. ## Meteoroids The word needed a boundary on each side, and the boundary has moved. The IAU's first definition, in 1961, called a meteoroid any solid body in interplanetary space much smaller than an asteroid and much larger than an atom, which left both limits open.[^millman1961] Martin Beech and Duncan Steel proposed in 1995 to fix the range at 100 micrometres to 10 metres.[^beech1995] That upper limit soon failed, because telescopes began finding asteroids smaller than 10 m. Alan Rubin and Jeffrey Grossman argued in 2010 that the practical smallest asteroid is set by what surveys can detect, and proposed 10 micrometres to 1 metre instead.[^rubin2010] Asteroids such as 2009 VA, about a metre across, now sit right at the dividing line.[^yeomans2009][^jpl-sbdb] The 2017 IAU revision set the range at 30 micrometres to 1 metre, with an exception for any larger object that produces a meteor; anything smaller is dust, or a micrometeoroid.[^imo2017][^imo-glossary] ### Composition Meteoroids are grouped the same way as the meteorites that reach the ground: irons, made mostly of [[Iron|iron]] and [[Nickel|nickel]] metal; stones; and stony-irons that mix the two. Stones that contain chondrules, small once-molten beads, are chondrites; stones without them, the achondrites, crystallised from melts inside a parent body and hold little metal.[^notkin] Bodies that burn up can still be analysed. The path of a meteor fixes the orbit and the deceleration, the [[Spectroscopy|spectrum]] of its light shows which elements are glowing, and radar echoes from the ionised trail extend the record to meteors that arrive in daylight. Such data show densities from fragile, porous bodies with about a quarter of the [[Density|density]] of ice to compact nickel-iron.[^povenmire2000] The orbits fall into two broad groups: streams that share the path of a parent comet, and sporadic meteoroids with no clear family. ### In the Solar System Most meteoroids begin in the [[Asteroid_belt|asteroid belt]] and are nudged onto planet-crossing orbits by the [[Gravity|gravity]] of the planets; the cometary ones come from the dust trails that feed showers.[^nasa-meteors] Their speeds follow from orbital mechanics. At Earth's distance from the [[Sun]], Earth moves at about 29.8 km/s, and a body on a parabolic [[Orbit|orbit]], just barely bound, moves faster by a factor of √2, about 42.1 km/s (derived).[^nasa-fs][^openstax] Nothing native to the Solar System can pass Earth's orbit faster than that. A meteoroid meeting Earth head-on, as those of the Leonid stream do on their retrograde orbit, therefore hits the air at up to about 42 + 30 ≈ 72 km/s (derived), while a slow one catching up from behind is accelerated by Earth's own pull to at least about 11 km/s. The mean speed of meteoroids near Earth's orbit is around 20 km/s.[^debris1989] A fireball over California and Nevada on 17 January 2013 showed the fast extreme: a body about a metre across on a retrograde orbit, likely from the [[Oort_cloud|Oort cloud]], struck at 72 ± 6 km/s and vaporised more than 100 km up.[^jenniskens2013] The explorer draws the dust near Earth and the Encke stream as sampled points: they are ILLUSTRATIVE, standing in for a population far too numerous to track, while the planets move on JPL elements.[^jpl-t1] ### Collision with Earth's atmosphere Entry converts [[Kinetic_energy|kinetic energy]] into heat and light through [[Drag_(physics)|drag]] on the thin upper air. A worked case shows the scale: a stony body 1 m across with an assumed density of 3,000 kg/m³ has a mass of about 1.6 tonnes, and at 20 km/s carries about 3 × 10¹¹ J, roughly the energy of 75 tonnes of TNT (derived). Most of that goes into ablating and fragmenting the body high in the atmosphere. On 6 October 2008 the 4 m asteroid 2008 TC3 became the first such body seen in space before it hit; it entered the next day over northern Sudan.[^imo-glossary] US government sensors recorded hundreds of small-asteroid fireballs between 1994 and 2013, scattered across the globe at random.[^jpl-map] ## Frequency Impact rates fall steeply with size, which is why small meteors are routine and large impacts rare. Peter Brown and colleagues combined satellite records of bright fireballs to fit the yearly number N of objects at least D metres across that strike Earth as log₁₀ N = 1.568 − 2.70 log₁₀ D.[^brown2002] The coefficients carry uncertainties of about 0.03 and 0.08. The formula is easy to evaluate. For D = 1 m it gives 10^1.568 ≈ 37 objects a year, about one every ten days (derived); ground networks such as the Desert Fireball Network report a similar 35–40 metre-scale impactors a year.[^devillepoix2019] For D = 4 m it gives about 0.9 a year, roughly one a year, and for D = 20 m about 0.011 a year, one in roughly 90 years (derived). The slope of 2.7 means that each doubling of diameter cuts the rate by a factor of 2^2.7 ≈ 6.5 (derived), while the mass of each impactor rises eightfold; across this size range the larger, rarer bodies therefore deliver slightly more of the total mass than the smaller, commoner ones (derived). On a single day the largest impactor is likely to be around 40 cm across.[^brown2002] Estimates of how much of this material reaches the ground as meteorites come from counts of fallen stones in deserts and from camera networks that recover freshly fallen ones.[^zolensky2006] A 2026 study simulated how the Rubin Observatory's Legacy Survey of Space and Time would have seen real metre-scale impactors in the days before they struck.[^frazer2026] ## Meteorites A meteorite is the part of a meteoroid, or of a larger asteroid, that survives its fall and lands intact.[^oxford1976] Large impacts often leave none. In the most energetic collisions the impactor vaporises, so hypervelocity craters may hold no meteorites at all. Geologists use the term "bolide" loosely for such a crater-forming body when its nature is unknown; the US Geological Survey applies it to any large projectile whose identity, stony or metal asteroid or icy comet, cannot be told.[^usgs-bolide] On the airless Moon, and on Mars with its thin atmosphere, meteoroids reach the surface with little or no braking, and their craters endure for very long times. On Earth, the atmosphere strips and slows most bodies long before they reach the surface, so meteorites are mostly the remnants of the larger or stronger ones. ### Impact craters Craters are the dominant landform on bodies whose surfaces change little, among them [[Mercury_(planet)|Mercury]], the Moon, [[Ganymede_(moon)|Ganymede]], [[Callisto_(moon)|Callisto]], most asteroids and most of the small moons. Where geology is active, as on Earth, [[Venus]], Mars, [[Europa_(moon)|Europa]], [[Io_(moon)|Io]] and [[Titan_(moon)|Titan]], craters are eroded, buried or deformed over time. Before impact cratering was widely recognised, some terrestrial structures now known to be impact scars were described as "cryptoexplosion" or "cryptovolcanic" features.[^french1998] Impacts also make new rock: melt thrown out of a crater can freeze into glassy tektites, often mistaken for meteorites, and rock shocked or melted in place, sometimes with fragments of the impactor, is called impactite.[^french1998] ### Gallery of meteorites The main families look different in hand. Irons are dense and heavy for their size, and cut and etched surfaces often show interlocking bands of nickel-iron crystals. Chondrites carry a dark fusion crust from entry over a grey interior dotted with chondrules. Achondrites resemble terrestrial igneous rocks, and stony-irons such as pallasites show crystals of green olivine set in metal.[^notkin] ## See also - [[Interplanetary_dust_cloud]] · [[Zodiacal_light]] · [[Meteor_shower]] - [[Asteroid]] · [[Comet]] · [[Near-Earth_object]] ### Relating to meteoroids - Micrometeoroid · [[Near-Earth_object]] · [[Interplanetary_dust_cloud]] ### Relating to meteorites - Impact crater · impact event · tektite · micrometeorite ## References [^imo2017]: Perlerin, V. (26 September 2017). "Definitions of terms in meteor astronomy (IAU)". *International Meteor Organization*. https://www.imo.net/definitions-of-terms-in-meteor-astronomy-iau/ [^imo-glossary]: International Meteor Organization. "Glossary". https://www.imo.net/glossary#letterm [^nasa-meteors]: NASA Solar System Exploration. "Meteors & Meteorites". https://science.nasa.gov/solar-system/meteors-meteorites/ [^rubin2010]: Rubin, A. E.; Grossman, J. N. (2010). "Meteorite and meteoroid: new comprehensive definitions". *Meteoritics & Planetary Science* 45: 114–122. https://doi.org/10.1111/j.1945-5100.2009.01009.x [^lidz2019]: Lidz, F. (9 January 2019). "The oldest material in the Smithsonian Institution came from outer space". *Smithsonian*. https://www.smithsonianmag.com/smithsonian-institution/oldest-material-smithsonian-institution-came-outer-space-180971017/ [^abc2011]: Gary, S. (22 December 2011). "Survey finds not all meteors the same". *ABC Science*. https://www.abc.net.au/science/articles/2011/12/22/3396756.htm [^millman1961]: Millman, P. M. (1961). "A report on meteor terminology". *Journal of the Royal Astronomical Society of Canada* 55: 265–267. Bibcode 1961JRASC..55..265M. [^beech1995]: Beech, M.; Steel, D. (1995). "On the definition of the term meteoroid". *Quarterly Journal of the Royal Astronomical Society* 36: 281–284. Bibcode 1995QJRAS..36..281B. [^yeomans2009]: Yeomans, D. K.; Chodas, P.; Chesley, S. (9 November 2009). "Small asteroid 2009 VA whizzes by the Earth". NASA Near-Earth Object Program Office. https://cneos.jpl.nasa.gov/news/news166.html [^jpl-sbdb]: JPL Solar System Dynamics. "Small-Body Database Lookup". https://ssd.jpl.nasa.gov/tools/sbdb_lookup.html (elements fetched 2026-09-18). [^notkin]: Notkin, G. "Meteorite types and classification". *Geology.com* (Meteorwritings). https://geology.com/meteorites/meteorite-types-and-classification.shtml [^povenmire2000]: Povenmire, H. (2000). "Physical dynamics of the Upsilon Pegasid fireball – European Network 190882A". *Lunar and Planetary Science Conference XXXI*, abstract 1183. https://www.lpi.usra.edu/meetings/lpsc2000/pdf/1183.pdf [^nasa-fs]: NASA NSSDCA. "Planetary Fact Sheet". https://nssdc.gsfc.nasa.gov/planetary/factsheet/ (fetched 2026-09-18). [^openstax]: Ling, S. J.; Sanny, J.; Moebs, W. (2016). *University Physics Volume 1*, ch. 13 "Gravitation". OpenStax. https://open.umn.edu/opentextbooks/textbooks/university-physics-volume-1 [^debris1989]: Interagency Group (Space) Working Group on Orbital Debris (February 1989). "Report on orbital debris". NASA Technical Reports Server. https://ntrs.nasa.gov/citations/19900003319 [^jenniskens2013]: Jenniskens, P. (2013). "2013 January 17 Sierra Nevada fireball". SETI Institute, CAMS. http://cams.seti.org/index-archive3.html [^jpl-t1]: JPL Solar System Dynamics. "Approximate Positions of the Planets", Table 1. https://ssd.jpl.nasa.gov/planets/approx_pos.html [^jpl-map]: NASA Jet Propulsion Laboratory (2014). "New map shows frequency of small asteroid impacts, provides clues on larger asteroid population". https://www.jpl.nasa.gov/news/new-map-shows-frequency-of-small-asteroid-impacts-provides-clues-on-larger-asteroid-population/ [^brown2002]: Brown, P.; Spalding, R. E.; ReVelle, D. O.; Tagliaferri, E.; Worden, S. P. (2002). "The flux of small near-Earth objects colliding with the Earth". *Nature* 420: 294–296. https://doi.org/10.1038/nature01238 [^devillepoix2019]: Devillepoix, H. A. R.; Bland, P. A.; Sansom, E. K.; Towner, M. C.; Cupák, M.; Howie, R. M.; et al. (2019). "Observation of metre-scale impactors by the Desert Fireball Network". *Monthly Notices of the Royal Astronomical Society* 483: 5166–5178. https://doi.org/10.1093/mnras/sty3442 [^zolensky2006]: Zolensky, M.; Bland, P. A.; Brown, P.; Halliday, I. (2006). "Flux of extraterrestrial materials". In Lauretta, D. S.; McSween, H. Y. (eds.), *Meteorites and the Early Solar System II*. University of Arizona Press, pp. 869–888. [^frazer2026]: Frazer, M.; Devillepoix, H.; Deam, S. (6 February 2026). "Simulated LSST observations of real metre-scale impactors". arXiv:2602.06314. http://arxiv.org/abs/2602.06314 [^oxford1976]: *The Oxford Illustrated Dictionary* (2nd ed., 1976). Oxford University Press, p. 533. [^usgs-bolide]: US Geological Survey. "What is a bolide?". https://woodshole.er.usgs.gov/epubs/bolide/introduction.html [^french1998]: French, B. M. (1998). *Traces of Catastrophe: A Handbook of Shock-Metamorphic Effects in Terrestrial Meteorite Impact Structures*. LPI Contribution 954, Lunar and Planetary Institute. http://www.lpi.usra.edu/publications/books/CB-954/CB-954.intro.html ## External links - NASA Science: Meteors and meteorites. https://science.nasa.gov/solar-system/meteors-meteorites/ - International Meteor Organization. https://www.imo.net/ - American Meteor Society. https://www.amsmeteors.org/ - NASA/JPL Center for Near Earth Object Studies: fireball data. https://cneos.jpl.nasa.gov/fireballs/ - Meteoritical Bulletin Database (Lunar and Planetary Institute). https://www.lpi.usra.edu/meteor/ ## Wikipedia : Wikitube **Strict pair:** [Wikipedia](https://en.wikipedia.org/wiki/Meteoroid) : [Wikitube](https://en.wikitube.io/wiki/Meteoroid) · pinned revision [1354793794](https://en.wikipedia.org/w/index.php?oldid=1354793794) · 2026-09-18 ## Previous hub tags Hubs: `Life_Physics`. 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