Editing Meteoroid (section)

=== 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 = http://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=http://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.