Editing Comet Shoemaker–Levy 9 (section)

== Frequency of impacts ==
{{Main|Impact events on Jupiter}}
[[File:Chain of impact craters on Ganymede.jpg|thumb|right|220px|[[Enki Catena]], a [[crater chain|chain of craters]] on [[Ganymede (moon)|Ganymede]], probably caused by a similar impact event. The picture covers an area approximately {{convert|190|km|abbr=on}} across]]

SL9 is not unique in having orbited Jupiter for a time; five comets, including [[82P/Gehrels]], [[147P/Kushida–Muramatsu]], and [[111P/Helin–Roman–Crockett]], are known to have been temporarily captured by the planet.<ref name="Ohtsukaetal2008">{{cite journal| bibcode = 2008A&A...489.1355O| title = Quasi-Hilda comet 147P/Kushida–Muramatsu. Another long temporary satellite capture by Jupiter| last1 = Ohtsuka| first1 = Katsuhito| journal = Astronomy and Astrophysics| volume = 489| issue = 3| date = October 2008| pages = 1355–1362| doi = 10.1051/0004-6361:200810321| last2 = Ito| first2 = T.| last3 = Yoshikawa| first3 = M.| last4 = Asher| first4 = D. J.| last5 = Arakida| first5 = H.|arxiv = 0808.2277 | s2cid = 14201751}}</ref><ref>{{cite journal|last1=Tancredi|first1=G. |date=November 1990 | title=Temporary Satellite Capture and Orbital Evolution of Comet P/Helin–Roman–Crockett |journal=[[Astronomy and Astrophysics]] |volume=239 |issue=1–2 |pages=375–380 |bibcode = 1990A&A...239..375T|last2=Lindgren|first2=M.|last3=Rickman|first3=H. }}</ref>
Cometary orbits around Jupiter are unstable, as they will be highly [[ellipse|elliptical]] and likely to be strongly [[Perturbation (astronomy)|perturbed]] by the Sun's gravity at [[apojove]] (the farthest point on the orbit from the planet).

By far the most massive planet in the [[Solar System]], Jupiter can capture objects relatively frequently, but the size of SL9 makes it a rarity: one post-impact study estimated that comets {{convert|0.3|km|abbr=on}} in diameter impact the planet once in approximately 500 years and those {{convert|1.6|km|abbr=on|sigfig=1}} in diameter do so just once in every 6,000 years.<ref>{{cite journal |last1=Roulston |first1=M.S. |date=March 1997 |title=Impact Mechanics and Frequency of SL9-Type Events on Jupiter |journal=[[Icarus (journal)|Icarus]] |volume=126 |issue=1 |pages=138–147 |doi=10.1006/icar.1996.5636 |last2=Ahrens |first2=T |bibcode=1997Icar..126..138R}}</ref>

There is very strong evidence that comets have previously been fragmented and collided with Jupiter and its satellites. During the Voyager missions to the planet, planetary scientists identified 13 [[crater chain]]s on [[Callisto (moon)|Callisto]] and three on [[Ganymede (moon)|Ganymede]], the origin of which was initially a mystery.<ref>{{cite journal |last1=Schenk |first1=Paul M. |date=June 1996 |title= Cometary Nuclei and Tidal Disruption: The Geologic Record of Crater Chains on Callisto and Ganymede |journal=[[Icarus (journal)|Icarus]] |volume=121 |issue=2 |pages=249–24 |doi=10.1006/icar.1996.0084 |bibcode=1996Icar..121..249S|last2=Asphaug |first2=Erik |last3=McKinnon |first3=William B. |last4=Melosh |first4=H. J. |last5=Weissman |first5=Paul R. |hdl=2060/19970022199 |hdl-access=free }}</ref> Crater chains seen on the [[Moon]] often radiate from large craters, and are thought to be caused by secondary impacts of the original ejecta, but the chains on the [[Jovian planet|Jovian]] moons did not lead back to a larger crater. The impact of SL9 strongly implied that the chains were due to trains of disrupted cometary fragments crashing into the satellites.<ref name="Greeley 2000">{{cite journal |last1=Greeley |first1=R. |title=Galileo views of the geology of Callisto |journal=Planetary and Space Science |year=2000 |volume=48 |issue=9 |pages=829–853 |bibcode=2000P&SS...48..829G |doi=10.1016/S0032-0633(00)00050-7 |last2=Klemaszewski |first2=J.E. |last3=Wagner |first3=R.|author4=the Galileo Imaging Team }}</ref>

=== Impact of July 19, 2009 ===
{{Main|2009 Jupiter impact event}}

On July 19, 2009, exactly 15 years after the SL9 impacts, a new black spot about the size of the Pacific Ocean appeared in Jupiter's southern hemisphere. Thermal infrared measurements showed the impact site was warm and spectroscopic analysis detected the production of excess hot ammonia and silica-rich dust in the upper regions of Jupiter's atmosphere. Scientists have concluded that another impact event had occurred, but this time a more compact and stronger object, probably a small undiscovered asteroid, was the cause.<ref>{{cite web|url=http://www.cnn.com/2009/TECH/space/07/21/jupiter.nasa.meteor.scar/index.html|title=Mystery impact leaves Earth-size mark on Jupiter - CNN.com|website=www.cnn.com}}</ref>