Editing Comet (section)

== Effects of comets ==
[[File:PSM V18 D201 Shower of perseids sept 6 and 7.jpg|thumb|Diagram of [[Perseids|Perseid meteors]]]]

=== Connection to meteor showers ===
As a comet is heated during close passes to the Sun, [[outgassing]] of its icy components releases solid debris too large to be swept away by [[radiation pressure]] and the solar wind.<ref>{{harvnb|Sagan|Druyan|1997|p=235}}</ref> If Earth's orbit sends it through that trail of debris, which is composed mostly of fine grains of rocky material, there is likely to be a [[meteor shower]] as Earth passes through. Denser trails of debris produce quick but intense meteor showers and less dense trails create longer but less intense showers. Typically, the density of the debris trail is related to how long ago the parent comet released the material.<ref name="sciam19990920">{{cite web |url=https://www.scientificamerican.com/article/what-causes-a-meteor-show/ |title=What causes a meteor shower? |work=[[Scientific American]] |first=Gregory A. |last=Lyzenga |date=20 September 1999 |access-date=21 November 2019}}</ref><ref name="natgeo20190207">{{cite web |url=https://www.nationalgeographic.com/science/space/reference/meteor-showers/ |archive-url=https://web.archive.org/web/20190507121359/https://www.nationalgeographic.com/science/space/reference/meteor-showers/ |url-status=dead |archive-date=7 May 2019 |title=Meteor showers, explained |work=[[National Geographic]] |first=Victoria |last=Jaggard |date=7 February 2019 |access-date=21 November 2019}}</ref> The [[Perseids|Perseid meteor shower]], for example, occurs every year between 9 and 13 August, when Earth passes through the orbit of [[Comet Swift–Tuttle]]. Halley's Comet is the source of the [[Orionids|Orionid shower]] in October.<ref name=showers>{{cite web |url=http://meteorshowersonline.com/major_meteor_showers.html |title=Major Meteor Showers |publisher=Meteor Showers Online |access-date=31 July 2013 |archive-url=https://web.archive.org/web/20130724111133/http://meteorshowersonline.com/major_meteor_showers.html |archive-date=24 July 2013 |url-status=dead}}</ref><ref>{{cite web |url=https://www.weather.gov/fsd/meteor |title=Meteors and Meteor Showers |publisher=United States National Weather Service |access-date=21 November 2019}}</ref>

=== Comets and impact on life ===

Many comets and asteroids collided with Earth in its early stages. Many scientists think that comets bombarding the young Earth about 4&nbsp;billion years ago brought the [[Origin of water on Earth|vast quantities of water]] that now fill Earth's oceans, or at least a significant portion of it. Others have cast doubt on this idea.<ref>{{cite web |last=Muir |first=Hazel |title=Earth's water brewed at home, not in space |url=https://www.newscientist.com/article/dn12693 |work=New Scientist |date=25 September 2007 |access-date=30 August 2013}}</ref> The detection of organic molecules, including [[polycyclic aromatic hydrocarbon]]s,<ref name="NASA-20150210">{{cite web |last=Clavin |first=Whitney |title=Why Comets Are Like Deep Fried Ice Cream |url=http://www.jpl.nasa.gov/news/news.php?feature=4480 |date=10 February 2015 |publisher=[[NASA]] |access-date=10 February 2015}}</ref> in significant quantities in comets has led to speculation that comets or [[meteorite]]s may have brought the precursors of life—or even life itself—to Earth.<ref>{{cite book |url=https://books.google.com/books?id=Dfn0VoICrBYC&pg=PA315 |page=315 |title=Comets |isbn=978-1-4020-3495-4 |last=Fernández |first=Julio A. |date=2006|publisher=Springer }}</ref> In 2013 it was suggested that impacts between rocky and icy surfaces, such as comets, had the potential to create the [[amino acid]]s that make up [[protein]]s through [[shock synthesis]].<ref>{{cite journal |doi=10.1038/ngeo1930 |title=Shock synthesis of amino acids from impacting cometary and icy planet surface analogues |date=2013 |last1=Martins |first1=Zita |last2=Price |first2=Mark C. |last3=Goldman |first3=Nir |last4=Sephton |first4=Mark A. |last5=Burchell |first5=Mark J. |display-authors=1 |journal=Nature Geoscience |bibcode=2013NatGe...6.1045M |volume=6 |issue=12 |pages=1045–1049}}</ref> The speed at which the comets entered the atmosphere, combined with the magnitude of energy created after initial contact, allowed smaller molecules to condense into the larger macro-molecules that served as the foundation for life.<ref>{{Cite web|url=https://www.astrobio.net/also-in-news/did-comet-impacts-jump-start-life-on-earth/|title=Did comet impacts jump-start life on Earth?|date=2019-10-18|website=Astrobiology Magazine|language=en-US|access-date=2019-12-01 |archive-url=https://web.archive.org/web/20210308143059/https://www.astrobio.net/also-in-news/did-comet-impacts-jump-start-life-on-earth/ |archive-date=2021-03-08 |url-status=usurped}}</ref> In 2015, scientists found significant amounts of molecular oxygen in the outgassings of comet 67P, suggesting that the molecule may occur more often than had been thought, and thus less an indicator of life as has been supposed.<ref>Oregonian (29 Oct 2015), "Comet's oxygen shakes theories on solar system", p. A5</ref>

It is suspected that comet impacts have, over long timescales, delivered significant quantities of water to Earth's [[Moon]], some of which may have survived as [[lunar ice]].<ref>{{cite web |url=http://lunarscience.nasa.gov/articles/water-discovered-in-apollo-moon-rocks-likely-came-from-comets/ |title=Water Discovered in Apollo Moon Rocks Likely Came from Comets |access-date=7 September 2013 |publisher=NASA}}</ref> Comet and [[meteoroid]] impacts are thought to be responsible for the existence of [[tektite]]s and [[australite]]s.<ref>{{cite web |url=http://museumvictoria.com.au/discoverycentre/infosheets/australites/ |archive-url=https://web.archive.org/web/20080726071448/http://museumvictoria.com.au/DiscoveryCentre/Infosheets/Australites/ |url-status=dead |archive-date=26 July 2008 |title=Australites |publisher=Museum Victoria |access-date=7 September 2013}}</ref>

===Fear of comets===
Fear of comets as [[act of God|acts of God]] and signs of impending doom was highest in Europe from AD 1200 to 1650.{{r|ley196710}} The year after the [[Great Comet of 1618]], for example, [[Gotthard Arthusius]] published a pamphlet stating that it was a sign that the [[Day of Judgment]] was near.<ref>{{cite book |url=https://gallica.bnf.fr/ark:/12148/btv1b2600275q |title=Cometa orientalis: Kurtze vnd eygentliche Beschreibung deß newen Cometen, so im November deß abgelauffenen 1618 |via=Gallica.fr |publisher=Sigismund Latomus |location=[[Frankfurt on Main|Franckfurt-am-Mayn]] |first=Gothard |last=Arthusius |author-link=Gotthard Arthusius |date=1619}}</ref> He listed ten pages of comet-related disasters, including "earthquakes, floods, changes in river courses, hail storms, hot and dry weather, poor harvests, epidemics, war and treason and high prices".{{r|ley196710}}

By 1700 most scholars concluded that such events occurred whether a comet was seen or not. Using [[Edmond Halley]]'s records of comet sightings, however, [[William Whiston]] in 1711 wrote that the [[Great Comet of 1680]] had a periodicity of 574 years and was responsible for the [[Genesis flood narrative|worldwide flood in the Book of Genesis]], by pouring water on Earth. His announcement revived for another century fear of comets, now as direct threats to the world instead of signs of disasters.<ref name="ley196710">{{Cite magazine |url=https://archive.org/stream/Galaxy_v26n01_1967-10_modified#page/n83/mode/2up |title=The Worst of All the Comets |department=For Your Information |magazine=[[Galaxy Science Fiction]] |last=Ley |first=Willy |volume=26 |issue=1 |pages=96–105 |date=October 1967}}</ref> Spectroscopic analysis in 1910 found the toxic gas [[cyanogen]] in the tail of Halley's Comet,<ref>{{Cite news |url=https://www.nytimes.com/1910/02/08/archives/comets-poisonous-tail-yerkes-observatory-finds-cyanogen-in-spectrum.html |title=Yerkes Observatory Finds Cyanogen in Spectrum of Halley's Comet |work=[[The New York Times]] |date=8 February 1910 |access-date=8 January 2018}}</ref> causing panicked buying of gas masks and quack "anti-comet pills" and "anti-comet umbrellas" by the public.<ref>{{Cite news |url=https://www.universetoday.com/40778/interesting-facts-about-comets/ |title=Interesting Facts About Comets |work=Universe Today |first=Jerry |last=Coffey |date=20 September 2009 |access-date=8 January 2018}}</ref>