Editing Comet Shoemaker–Levy 9 (section)

== Jupiter's role in protection of the inner Solar System ==
{{See also|Asteroid impact avoidance}}
The events of SL9's interaction with Jupiter greatly highlighted Jupiter's role in protecting the inner planets from both interstellar and in-system debris by acting as a "cosmic vacuum cleaner" for the Solar System ([[Jupiter barrier]]). The planet's strong gravitational influence attracts many small comets and [[asteroid]]s and the rate of cometary impacts on Jupiter is thought to be between 2,000 and 8,000 times higher than the rate on Earth.<ref name="Nakamura">{{cite journal |last1=Nakamura |first1=T. |date=February 1998 |title=Collisional Probability of Periodic Comets with the Terrestrial Planets – an Invalid Case of Analytic Formulation |journal=Astronomical Journal |volume=115 |issue=2 |pages=848 |bibcode=1998AJ....115..848N |quote=For Jupiter-interacting comets of greater than 1 km diameter, a Jupiter impact takes place every 500–1000 yr, and an Earth impact every 2–4 Myr. |doi=10.1086/300206 |last2=Kurahashi |first2=H.|doi-access=free }}</ref>

The extinction of the non-avian [[dinosaurs]] at the end of the [[Cretaceous]] period is generally thought to have been caused by the [[Cretaceous–Paleogene extinction event|Cretaceous–Paleogene impact event]], which created the [[Chicxulub crater]],<ref name="Chicxulub">{{cite web |date=August 22, 2005 |title=PIA01723: Space Radar Image of the Yucatan Impact Crater Site |publisher=NASA/JPL Near-Earth Object Program Office |url=https://photojournal.jpl.nasa.gov/catalog/PIA01723 |access-date=July 21, 2009 | archive-url = https://web.archive.org/web/20160808224949/http://neo.jpl.nasa.gov/images/yucatan.html | archive-date = August 8, 2016 }}</ref> demonstrating that cometary impacts are indeed a serious threat to life on Earth. Astronomers have speculated that without Jupiter's immense gravity, extinction events might have been more frequent on Earth and complex life might not have been able to develop.<ref name="Wetherill">{{cite journal |first=George W. |last=Wetherill |author-link=George Wetherill |title=Possible consequences of absence of "Jupiters" in planetary systems |journal=[[Astrophysics and Space Science]] |volume=212 |issue=1–2 |pages=23–32 |date=February 1994 |pmid=11539457 |doi=10.1007/BF00984505 |bibcode=1994Ap&SS.212...23W|s2cid=21928486 }}</ref> This is part of the argument used in the [[Rare Earth hypothesis]].

In 2009, it was shown that the presence of a smaller planet at Jupiter's position in the Solar System might increase the impact rate of comets on the Earth significantly. A planet of Jupiter's mass still seems to provide increased protection against asteroids, but the total effect on all orbital bodies within the Solar System is unclear. This and other recent models call into question the nature of Jupiter's influence on Earth impacts.<ref>{{cite journal |last1=Horner |first1=J. |last2=Jones |first2=B. W. |date=2008 |title=Jupiter – friend or foe? I: The asteroids |journal=[[International Journal of Astrobiology]] |volume=7 |issue=3–4 |pages=251–261 |doi=10.1017/S1473550408004187 |bibcode = 2008IJAsB...7..251H |arxiv = 0806.2795 |s2cid=8870726 }}</ref><ref>{{cite journal |last1=Horner |first1=J. |last2=Jones |first2=B. W. |title=Jupiter – friend or foe? II: the Centaurs Jupiter |journal=[[International Journal of Astrobiology]] |volume=8 |issue=2 |pages=75–80 |arxiv=0903.3305 |bibcode=2009IJAsB...8...75H |doi= 10.1017/S1473550408004357|year=2009 |s2cid=8032181 }}</ref><ref>{{cite journal |last=Grazier |first=Kevin R. |s2cid=23859604 |date=January 2016 |title=Jupiter: Cosmic Jekyll and Hyde |journal=[[Astrobiology (journal)|Astrobiology]] |volume=16 |issue=1 |pages=23–38 |doi=10.1089/ast.2015.1321 |pmid=26701303 |bibcode = 2016AsBio..16...23G }}</ref>