Editing Meteor shower (section)

==Origin of meteoroid streams ==
[[File:Ssc2005-04a medium.jpg|thumb|[[Comet Encke]]'s meteoroid trail is the diagonal red glow.]]
[[File:Sig06-011 medium.jpg|thumb|Meteoroid trail between fragments of [[Comet 73P]]]]

A meteor shower results from an interaction between a planet, such as Earth, and streams of debris from a [[comet]] (or occasionally an [[asteroid]]). Comets can produce debris by water vapor drag, as demonstrated by [[Fred Whipple]] in 1951,<ref>{{Cite journal |last=Whipple |first=F. L. |year=1951 |title=A Comet Model. II. Physical Relations for Comets and Meteors |journal=Astrophys. J. |volume=113 |page=464 |bibcode=1951ApJ...113..464W |doi=10.1086/145416|doi-access=free }}</ref> and by breakup. Whipple envisioned comets as "dirty snowballs", made up of rock embedded in ice, orbiting the [[Sun]]. The "ice" may be [[water]], [[methane]], [[ammonia]], or other [[Volatile (astrogeology)|volatiles]], alone or in combination. The "rock" may vary in size from a dust mote to a small boulder. Dust mote sized solids are [[orders of magnitude]] more common than those the size of sand grains, which, in turn, are similarly more common than those the size of pebbles, and so on. When the ice warms and sublimates, the vapor can drag along dust, sand, and pebbles.

Each time a comet swings by the Sun in its [[orbit]], some of its ice vaporizes, and a certain number of meteoroids will be shed. The meteoroids spread out along the entire trajectory of the comet to form a meteoroid stream, also known as a "dust trail" (as opposed to a comet's "gas tail" caused by the tiny particles that are quickly blown away by solar radiation pressure).

Recently, [[Peter Jenniskens]]<ref name="Jenniskens P. 2006">Jenniskens P. (2006). ''Meteor Showers and their Parent Comets''. Cambridge University Press, Cambridge, U.K., 790 pp.</ref> has argued that most of our short-period meteor showers are not from the normal water vapor drag of active comets, but the product of infrequent disintegrations, when large chunks break off a mostly dormant comet. Examples are the [[Quadrantids]] and [[Geminids]], which originated from a breakup of asteroid-looking objects, {{mpl|196256|2003 EH|1}} and [[3200 Phaethon]], respectively, about 500 and 1000 years ago. The fragments tend to fall apart quickly into dust, sand, and pebbles and spread out along the comet's orbit to form a dense meteoroid stream, which subsequently evolves into Earth's path.