View source for Comet Shoemaker–Levy 9

{{Short description|Comet that collided with Jupiter}}
{{For|other comets discovered by Carolyn and Eugene Shoemaker, and David H. Levy|Comet Shoemaker|Comet Levy}}

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{{Use mdy dates|date=July 2019}}
{{Infobox comet
| name = D/1993 F2 (Shoemaker–Levy)
| image = Shoemaker-Levy 9 on 1994-05-17.png
| image_scale = 1.67
| discovery_site     = [[Palomar Observatory]]
| caption = {{Longitem|Shoemaker–Levy&nbsp;9, [[Comet#Breakup and collisions|disrupted comet]] on a collision course<ref>{{Cite web |last=Howell |first=E. |date=February 19, 2013 |url=http://www.space.com/19855-shoemaker-levy-9.html |work=[[Space.com]] |title=Shoemaker–Levy 9: Comet's Impact Left Its Mark on Jupiter}}</ref><ref>{{Cite web|title=Panoramic Picture of Comet P/Shoemaker-Levy 9|url=http://hubblesite.org/contents/media/images/1994/26/168-Image|access-date=2021-12-03|website=HubbleSite.org|language=en}}</ref><br />(total of 21 fragments, taken in July 1994)|style=padding: 4px 0 6px;}}
| discoverer = [[Carolyn S. Shoemaker|Carolyn Shoemaker]]<br />[[Eugene Merle Shoemaker|Eugene Shoemaker]]<br />[[David H. Levy|David Levy]]
| discovery_date = March 24, 1993
| inclination = 94.2°
| dimensions = {{Convert|1.8|km|abbr=on}}<ref name=Solem1995/><ref name=Solem1994/>
}}

'''Comet Shoemaker–Levy 9''' ([[Astronomical naming conventions#Comets|formally designated]] '''D/1993&nbsp;F2''') was a [[comet]] that broke apart in July 1992 and collided with [[Jupiter]] in July 1994, providing the first direct observation of an extraterrestrial [[collision]] of [[Solar System]] objects.<ref name="NASA2005">{{cite web |url=http://nssdc.gsfc.nasa.gov/planetary/comet.html |title=Comet Shoemaker–Levy 9 Collision with Jupiter |access-date=August 26, 2008 |publisher=[[National Space Science Data Center]] |date=February 2005 |archive-url=https://web.archive.org/web/20130219011148/http://nssdc.gsfc.nasa.gov/planetary/comet.html |archive-date=February 19, 2013 |url-status=dead  }}</ref> This generated a large amount of coverage in the popular media, and the comet was closely observed by [[astronomer]]s worldwide. The collision provided new information about Jupiter and highlighted its possible role in reducing space debris in the [[Solar System#Inner planets|inner Solar System]].

The comet was discovered by astronomers [[Carolyn S. Shoemaker|Carolyn]] and [[Eugene Merle Shoemaker|Eugene M. Shoemaker]], and [[David H. Levy|David Levy]] in 1993.<ref name="IAU 5725" /> Shoemaker–Levy 9 (SL9) had been captured by Jupiter and was orbiting the planet at the time. It was located on the night of March 24 in two photographs taken with the {{convert|46|cm|in|abbr=on}} [[Schmidt camera|Schmidt telescope]] at the [[Palomar Observatory]] in [[California]]. It was the first active comet observed to be orbiting a planet, and had probably been captured by Jupiter around 20 to 30 years earlier.

Calculations showed that its unusual fragmented form was due to a previous closer approach to Jupiter in July 1992. At that time, the orbit of Shoemaker–Levy 9 passed within Jupiter's [[Roche limit]], and Jupiter's [[tidal force]]s had acted to pull the comet apart. The comet was later observed as a series of fragments ranging up to {{convert|2|km|abbr=on}} in diameter. These fragments collided with Jupiter's southern hemisphere between July 16 and 22, 1994 at a speed of approximately {{convert|60|km/s|0|abbr=on}} (Jupiter's [[escape velocity]]) or {{convert|216000|km/h|mph|abbr=on}}. The prominent scars from the impacts were more visible than the [[Great Red Spot]] and persisted for many months.

== Discovery ==
While conducting a program of observations designed to uncover [[near-Earth object]]s, the Shoemakers and Levy discovered Comet Shoemaker–Levy 9 on the night of March 24, 1993, in two photographs taken with the {{convert|46|cm|ft|abbr=on}} [[Schmidt telescope]] at the [[Palomar Observatory]] in [[California]]. The comet was thus a serendipitous discovery, but one that quickly overshadowed the results from their main observing program.<ref name="Marsden1">{{cite web |url=http://www2.jpl.nasa.gov/sl9/news81.html |title=Eugene Shoemaker (1928–1997) |access-date=August 24, 2008 |last=Marsden |first=Brian G. |date=July 18, 1997 |publisher=[[Jet Propulsion Laboratory]]}}</ref>

Comet Shoemaker–Levy 9 was the ninth periodic comet (a comet whose orbital period is 200 years or less) discovered by the Shoemakers and Levy, [[naming of comets|thence its name]]. It was their eleventh comet discovery overall including their discovery of two non-periodic comets, which use a different nomenclature. The discovery was announced in [[IAU Circular]] 5725 on March 26, 1993.<ref name="IAU 5725">{{cite journal |last= Marsden |first=B. G.|url=http://www.cbat.eps.harvard.edu/iauc/05700/05725.html#Item1 |title=Comet Shoemaker-Levy (1993e) |journal=IAU Circular |issue=5725 |year=1993 }}</ref>

The discovery image gave the first hint that comet Shoemaker–Levy 9 was an unusual comet, as it appeared to show multiple nuclei in an elongated region about 50&nbsp;[[arcsecond]]s long and 10&nbsp;arcseconds wide. [[Brian G. Marsden]] of the [[Central Bureau for Astronomical Telegrams]] noted that the comet lay only about 4&nbsp;[[degree (angle)|degrees]] from Jupiter as seen from Earth, and that although this could be a line-of-sight effect, its apparent motion in the sky suggested that the comet was physically close to the planet.<ref name="IAU 5725"/>

== Comet with a Jovian orbit ==
Orbital studies of the new comet soon revealed that it was orbiting [[Jupiter]] rather than the [[Sun]], unlike any other comet then known. Its orbit around Jupiter was very loosely bound, with a period of about 2 years and an [[apoapsis]] (the point in the orbit farthest from the planet) of {{convert|0.33|AU|e6km+e6mi|lk=in|abbr=off}}. Its orbit around the planet was highly [[Orbital eccentricity|eccentric]] (''e'' = 0.9986).<ref name="Bruton1.4" />

Tracing back the comet's orbital motion revealed that it had been orbiting Jupiter for some time. It is likely that it was captured from a solar orbit in the early 1970s, although the capture may have occurred as early as the mid-1960s.<ref name="Landis">{{cite web |url=http://www.seds.org/sl9/landis.html |title=Comet P/Shoemaker–Levy's Collision with Jupiter: Covering HST's Planned Observations from Your Planetarium |access-date=August 8, 2008 |last=Landis |first=R. R. |year=1994 |work=Proceedings of the International Planetarium Society Conference held at the Astronaut Memorial Planetarium & Observatory, Cocoa, Florida, July 10–16, 1994 |publisher=[[Students for the Exploration and Development of Space|SEDS]]|archive-url = https://web.archive.org/web/20080808142753/http://www.seds.org/sl9/landis.html |archive-date=August 8, 2008 }}</ref> Several other observers found images of the comet in [[precovery]] images obtained before March 24, including [[Kin Endate]] from a photograph exposed on March 15, [[Satoru Otomo]] on March 17, and a team led by [[Eleanor Helin]] from images on March 19.<ref name="D1993">{{cite web|url=http://cometography.com/pcomets/1993f2.html |title=D/1993 F2 Shoemaker–Levy 9 |access-date=August 8, 2008 |year=1994 |work=Gary W. Kronk's Cometography |url-status=dead |archive-url=https://web.archive.org/web/20080509145539/http://cometography.com/pcomets/1993f2.html |archive-date=May 9, 2008 }}</ref> An image of the comet on a Schmidt photographic plate taken on March 19 was identified on March 21 by M. Lindgren, in a project searching for comets near Jupiter.<ref>{{Cite journal|last=Lindgren|first=Mats|date=August 1996|title=Searching for comets encountering Jupiter. Second campaign observations and further constraints on the size of the Jupiter family population.|journal=Astronomy and Astrophysics Supplement Series|volume=118|issue=2|pages=293–301|doi=10.1051/aas:1996198|bibcode=1996A&AS..118..293L|doi-access=free}}</ref> However, as his team were expecting comets to be inactive or at best exhibit a weak dust coma, and SL9 had a peculiar morphology, its true nature was not recognised until the official announcement 5 days later. No precovery images dating back to earlier than March 1993 have been found. Before the comet was captured by Jupiter, it was probably a short-period comet with an [[aphelion]] just inside Jupiter's orbit, and a [[perihelion]] interior to the [[asteroid belt]].<ref name="Benner">{{cite journal |last1=Benner |first1=L. A. |date=March 1994 |title=Pre-Impact Orbital Evolution of P/Shoemaker–Levy 9 |journal=Abstracts of the 25th Lunar and Planetary Science Conference, Held in Houston, TX, March 14–18, 1994 |volume=25 |page=93 |bibcode=1994LPI....25...93B |last2=McKinnon |first2=W. B.}}</ref>

The volume of space within which an object can be said to orbit Jupiter is defined by Jupiter's [[Hill sphere]]. When the comet passed Jupiter in the late 1960s or early 1970s, it happened to be near its aphelion, and found itself slightly within Jupiter's Hill sphere. Jupiter's gravity nudged the comet towards it. Because the comet's motion with respect to Jupiter was very small, it fell almost straight toward Jupiter, which is why it ended up on a Jove-centric orbit of very high eccentricity—that is to say, the ellipse was nearly flattened out.<ref name="Chapman">{{cite journal |last=Chapman |first=C. R. |date=June 1993 |title=Comet on target for Jupiter |journal=Nature |volume=363 |issue=6429 |pages=492–493 |doi=10.1038/363492a0|bibcode = 1993Natur.363..492C |s2cid=27605268 |doi-access=free }}</ref>

The comet had apparently passed extremely close to Jupiter on July 7, 1992, just over {{convert|40000|km|abbr=on}} above its cloud tops—a smaller distance than Jupiter's radius of {{convert|70000|km|abbr=on}}, and well within the orbit of Jupiter's innermost moon [[Metis (moon)|Metis]] and the planet's [[Roche limit]], inside which [[tidal force]]s are strong enough to disrupt a body held together only by gravity.<ref name="Chapman" /> Although the comet had approached Jupiter closely before, the July 7 encounter seemed to be by far the closest, and the fragmentation of the comet is thought to have occurred at this time. Each fragment of the comet was denoted by a letter of the alphabet, from "fragment A" through to "fragment W", a practice already established from previously observed fragmented comets.<ref name="Boehnhardt">{{Cite book |first=H. |last=Boehnhardt |date=November 2004 |chapter=Split comets |title=Comets II |editor=M. C. Festou, H. U. Keller and H. A. Weaver |publisher=[[University of Arizona Press]] |page=301 |isbn=978-0-8165-2450-1}}</ref>

More exciting for planetary astronomers was that the best orbital calculations suggested that the comet would pass within {{convert|45000|km|abbr=on}} of the center of Jupiter, a distance smaller than the planet's radius, meaning that there was an extremely high probability that SL9 would collide with Jupiter in July 1994.<ref name="IAU 5800">{{cite journal |last=Marsden |first=B. G. |title=Periodic Comet Shoemaker-Levy 9 (1993e) |url=http://www.cbat.eps.harvard.edu/iauc/05800/05800.html#Item1 |journal=IAU Circular |issue= 5800 |year=1993}}</ref> Studies suggested that the train of nuclei would plow into Jupiter's atmosphere over a period of about five days.<ref name="Chapman" />

== Predictions for the collision ==
The discovery that the comet was likely to collide with Jupiter caused great excitement within the astronomical community and beyond, as astronomers had never before seen two significant Solar System bodies collide. Intense studies of the comet were undertaken, and as its orbit became more accurately established, the possibility of a collision became a certainty. The collision would provide a unique opportunity for scientists to look inside Jupiter's atmosphere, as the collisions were expected to cause eruptions of material from the layers normally hidden beneath the clouds.<ref name="Bruton1.4">{{cite web |first=Dan |last=Burton |url=http://www.physics.sfasu.edu/astro/sl9/cometfaq.html#Q1.4 |title=What will be the effect of the collision? |work=Frequently Asked Questions about the Collision of Comet Shoemaker–Levy 9 with Jupiter |publisher=[[Stephen F. Austin State University]] |date=July 1994 |access-date=August 20, 2008 |url-status=dead |archive-url=https://web.archive.org/web/20121209023201/http://www.physics.sfasu.edu/astro/sl9/cometfaq.html |archive-date=December 9, 2012  }}</ref>

Astronomers estimated that the visible fragments of SL9 ranged in size from a few hundred metres (around {{convert|300|m|abbr=on|disp=out|sigfig=1}}) to {{convert|2|km|spell=in}} across, suggesting that the original comet may have had a nucleus up to {{convert|5|km|abbr=on}} across—somewhat larger than [[Comet Hyakutake]], which became very bright when it passed close to the Earth in 1996. One of the great debates in advance of the impact was whether the effects of the impact of such small bodies would be noticeable from Earth, apart from a flash as they disintegrated like giant [[Meteoroid|meteors]].<ref name="Bruton1.5">{{cite web |first=Dan |last=Bruton |url=http://www.physics.sfasu.edu/astro/sl9/cometfaq.html#Q1.5 |title=Can I see the effects with my telescope? |work=Frequently Asked Questions about the Collision of Comet Shoemaker–Levy 9 with Jupiter |publisher=[[Stephen F. Austin State University]] |date=July 1994 |access-date=August 20, 2008 |url-status=dead |archive-url=https://web.archive.org/web/20121209023201/http://www.physics.sfasu.edu/astro/sl9/cometfaq.html |archive-date=December 9, 2012  }}</ref> The most optimistic prediction was that large, asymmetric [[bolide|ballistic fireballs]] would rise above the limb of Jupiter and into sunlight to be visible from Earth.<ref name="Boslough">{{cite journal |last1=Boslough |first1=Mark B. |date=July 5, 1994 |title=Watching for Fireballs on Jupiter |journal=Eos, Transactions, American Geophysical Union |volume=75 | number=27|page=305 | last2=Crawford |first2=David A. |last3=Robinson |first3=Allen C. |last4=Trucano |first4=Timothy G. |doi=10.1029/94eo00965|bibcode = 1994EOSTr..75..305B }}</ref>
Other suggested effects of the impacts were [[Seismology|seismic]] waves travelling across the planet, an increase in [[stratosphere|stratospheric]] haze on the planet due to dust from the impacts, and an increase in the mass of the [[Rings of Jupiter|Jovian ring system]]. However, given that observing such a collision was completely unprecedented, astronomers were cautious with their predictions of what the event might reveal.<ref name="Bruton1.4" />

== Impacts ==
[[File:Hubble Space Telescope Image of Fragment BDGLNQ12R Impacts.png|left|thumb|Jupiter in [[ultraviolet]] (about 2.5 hours after R's impact). The black dot near the top is [[Io (moon)|Io]] transiting Jupiter.<ref>{{cite web|url=http://hubblesite.org/image/180/news_release/1994-35|title=Hubble Ultraviolet Image of Multiple Comet Impacts on Jupiter|work=News Release Number: STScI-1994-35|date=July 23, 1994|publisher=Hubble Space Telescope Comet Team|access-date=November 12, 2014|archive-url=https://web.archive.org/web/20171205042113/http://hubblesite.org/image/180/news_release/1994-35|archive-date=December 5, 2017|url-status=dead}}</ref>]]

Anticipation grew as the predicted date for the collisions approached, and astronomers trained terrestrial telescopes on Jupiter. Several space observatories did the same, including the [[Hubble Space Telescope]], the [[ROSAT]] [[X-ray]]-observing [[satellite]], the [[W. M. Keck Observatory]], and the [[Galileo (spacecraft)|''Galileo'' spacecraft]], then on its way to a rendezvous with Jupiter scheduled for 1995. Although the impacts took place on the side of Jupiter hidden from Earth, ''Galileo'', then at a distance of {{convert|1.6|AU|e6km+e6mi|abbr=unit}} from the planet, was able to see the impacts as they occurred. Jupiter's rapid rotation brought the impact sites into view for terrestrial observers a few minutes after the collisions.<ref name="Chodas">
{{cite journal
 |last=Yeomans
 |first=D.K.
 |date=December 1993
 |title=Periodic comet Shoemaker–Levy 9 (1993e)
 |journal=IAU Circular
 |issue=5909
 |url=http://www.cbat.eps.harvard.edu/iauc/05900/05909.html#Item2
 |access-date=July 5, 2011
}}</ref>

Two other space probes made observations at the time of the impact: the [[Ulysses (spacecraft)|''Ulysses'' spacecraft]], primarily designed for [[Sun|solar]] observations, was pointed toward Jupiter from its location {{convert|2.6|AU|e6km+e6mi|abbr=unit}} away, and the distant ''[[Voyager 2]]'' probe, some {{convert|44|AU|e9km+e9mi|abbr=unit}} from Jupiter and on its way out of the Solar System following its encounter with [[Neptune]] in 1989, was programmed to look for radio emission in the 1–390&nbsp;[[kHz]] range and make observations with its ultraviolet spectrometer.<ref name=williamsnasa>{{cite web |url=http://nssdc.gsfc.nasa.gov/planetary/others.html |last=Williams |first=David R. |title=Ulysses and Voyager 2 |access-date=August 25, 2008 |work=Lunar and Planetary Science |publisher=[[National Space Science Data Center]] |archive-date=October 24, 2008 |archive-url=https://web.archive.org/web/20081024123110/http://nssdc.gsfc.nasa.gov/planetary/others.html |url-status=dead }}</ref>

[[File:Impact fireball appears over the limb of Jupiter.jpg|thumb|150px|Hubble Space Telescope images of a [[Fireball (meteor)|fireball]] from the first impact appearing over the limb of the planet]]
[[File:Animation of Shoemaker-Levy 9's orbit around Jupiter.gif|thumb|Animation of Shoemaker-Levy 9's orbit around Jupiter<br>{{legend2|Lime|Jupiter}}{{·}}{{legend2| Magenta| Fragment A}}{{·}}{{legend2|RoyalBlue|Fragment D}}{{·}}{{legend2|Cyan|Fragment G}}{{·}}{{legend2|Gold|Fragment N}}{{·}}{{legend2|OrangeRed|Fragment W}}]]
Astronomer [[Ian Morison]] described the impacts as following:
<blockquote>The first impact occurred at 20:13&nbsp;[[Coordinated Universal Time|UTC]] on July 16, 1994, when fragment A of the [[comet nucleus|[comet's] nucleus]] slammed into Jupiter's southern hemisphere at about {{convert|60|km/s|abbr=on|round=5}}. Instruments on ''Galileo'' detected a [[Fireball (meteor)|fireball]] that reached a peak temperature of about {{convert|24,000|K|lk=in}}, compared to the typical Jovian cloud-top temperature of about {{convert|130|K|lk=in}}. It then expanded and cooled rapidly to about {{convert|1500|K}}. The plume from the fireball quickly reached a height of over {{convert|3000|km|abbr=on}} and was observed by the HST.<ref>{{cite book |last1=Morison |first1=Ian |title=A Journey through the Universe: Gresham Lectures on Astronomy |date=25 September 2014 |publisher=Cambridge University Press |isbn=978-1-316-12380-5 |page=110 |url=https://books.google.com/books?id=GZx7BAAAQBAJ&dq=sl9+jupiter+24000+k&pg=PA110 |access-date=12 January 2022 |language=en}}</ref><ref name="Martin">{{cite journal |last=Martin |first=Terry Z. |date=September 1996 |title=Shoemaker–Levy 9: Temperature, Diameter and Energy of Fireballs |journal=Bulletin of the American Astronomical Society |volume=28 |page=1085 |bibcode=1996DPS....28.0814M}}</ref></blockquote>

A few minutes after the impact fireball was detected, ''Galileo'' measured renewed heating, probably due to ejected material falling back onto the planet. Earth-based observers detected the fireball rising over the limb of the planet shortly after the initial impact.<ref name="Weissman">{{cite journal |last1=Weissman |first1=P.R. |date=March 1995 |title=Galileo NIMS Direct Observation of the Shoemaker–Levy 9 Fireballs and Fall Back |journal=Abstracts of the Lunar and Planetary Science Conference |volume=26 |page=1483 |bibcode=1995LPI....26.1483W |last2=Carlson |first2=R. W. |last3=Hui |first3=J. |last4=Segura |first4=M. |last5=Smythe |first5=W. D. |last6=Baines |first6=K. H. |last7=Johnson |first7=T. V. |last8=Drossart |first8=P. |last9=Encrenaz |first9=T.|author9-link=Thérèse Encrenaz|last10=Leader |first10=F. |last11=Mehlman |first11=R. |display-authors=9 }}</ref>

Despite published predictions,<ref name="Boslough" /> astronomers had not expected to see the fireballs from the impacts<ref name="Fizzle">{{cite journal |last=Weissman |first=Paul |date=July 14, 1994 |title= The Big Fizzle is coming |journal=Nature |volume=370 |issue=6485 | pages=94–95 |doi=10.1038/370094a0|bibcode = 1994Natur.370...94W |s2cid=4358549 |doi-access=free }}</ref> and did not have any idea how visible the other atmospheric effects of the impacts would be from Earth. Observers soon saw a huge dark spot after the first impact; the spot was visible from Earth. This and subsequent dark spots were thought to have been caused by debris from the impacts, and were markedly asymmetric, forming crescent shapes in front of the direction of impact.<ref name="Hammel">{{Cite conference |last=Hammel |first=H.B. |date=December 1994 |title=The Spectacular Swan Song of Shoemaker–Levy 9 |conference=185th AAS Meeting |publisher=American Astronomical Society |volume=26 |pages=1425 |bibcode=1994AAS...185.7201H}}</ref>

Over the next six days, 21 distinct impacts were observed, with the largest coming on July 18 at 07:33 UTC when fragment G struck Jupiter. This impact created a giant dark spot over {{cvt|12000|km|disp=or}}<ref>{{cite web |title=Remembering Comet Shoemaker-Levy 9's Impact on Jupiter, 23 Years Ago This Week |url=https://www.americaspace.com/2017/07/17/remembering-comet-shoemaker-levy-9s-impact-on-jupiter-23-years-ago-this-week/ |website=AmericaSpace |access-date=12 January 2022 |date=17 July 2017}}</ref> (almost one [[Earth radius#Derived quantities: diameter, circumference, arc-length, area, volume|Earth diameter]]) across, and was estimated to have released an energy equivalent to 6,000,000&nbsp;[[TNT equivalent|megatons of TNT]] (600 times the world's nuclear arsenal).<ref>{{cite web |first=Dan |last=Bruton |url=http://www.physics.sfasu.edu/astro/sl9/cometfaq2.html#Q3.1 |title=What were some of the effects of the collisions? |work=Frequently Asked Questions about the Collision of Comet Shoemaker–Levy 9 with Jupiter |publisher=[[Stephen F. Austin State University]] |date=February 1996 |access-date=January 27, 2014 |archive-date=August 28, 2021 |archive-url=https://web.archive.org/web/20210828080844/http://www.physics.sfasu.edu/astro/sl9/cometfaq2.html#Q3.1 |url-status=dead }}</ref> Two impacts 12&nbsp;hours apart on July 19 created impact marks of similar size to that caused by fragment G, and impacts continued until July 22, when fragment W struck the planet.<ref>{{cite web |first=Don |last=Yeomans |author2=Chodas, Paul |url=http://www2.jpl.nasa.gov/sl9/impacts4.html | title=Comet Crash Impact Times Request |publisher=[[Jet Propulsion Laboratory]] |date=March 18, 1995 |access-date=August 26, 2008}}</ref>

== Observations and discoveries ==

=== Chemical studies ===
[[File:Jupiter showing SL9 impact sites.jpg|250px|thumb|Brown spots mark impact sites on [[Jupiter]]'s southern hemisphere]]

Observers hoped that the impacts would give them a first glimpse of Jupiter beneath the cloud tops, as lower material was exposed by the comet fragments punching through the upper atmosphere. [[Astronomical spectroscopy|Spectroscopic]] studies revealed [[Spectral line|absorption lines]] in the Jovian spectrum due to [[disulfur|diatomic sulfur]] (S<sub>2</sub>) and [[carbon disulfide]] (CS<sub>2</sub>), the first detection of either in Jupiter, and only the second detection of S<sub>2</sub> in any [[astronomical object]]. Other molecules detected included [[ammonia]] (NH<sub>3</sub>) and [[hydrogen sulfide]] (H<sub>2</sub>S). The amount of sulfur implied by the quantities of these compounds was much greater than the amount that would be expected in a small cometary nucleus, showing that material from within Jupiter was being revealed. [[Oxygen]]-bearing molecules such as [[sulfur dioxide]] were not detected, to the surprise of astronomers.<ref name="McGrath">{{cite journal |last1=Noll |first1=K.S. |date=March 1995 |title=HST Spectroscopic Observations of Jupiter Following the Impact of Comet Shoemaker–Levy 9 |journal=Science |volume=267 |issue=5202 |pages=1307–1313 |doi=10.1126/science.7871428 |pmid=7871428 |last2=McGrath |first2=MA |last3=Trafton |first3=LM |last4=Atreya |first4=SK |last5=Caldwell |first5=JJ |last6=Weaver |first6=HA |last7=Yelle |first7=RV |last8=Barnet |first8=C |last9=Edgington |first9=S|bibcode = 1995Sci...267.1307N |s2cid=37686143 }}</ref>

As well as these [[molecule]]s, emission from heavy [[atom]]s such as [[iron]], [[magnesium]] and [[silicon]] were detected, with abundances consistent with what would be found in a cometary nucleus. Although a substantial amount of water was detected spectroscopically, it was not as much as predicted, meaning that either the water layer thought to exist below the clouds was thinner than predicted, or that the cometary fragments did not penetrate deeply enough.<ref name="Hu" />

=== Waves ===
As predicted, the collisions generated enormous waves that swept across Jupiter at speeds of {{convert|450|m/s|abbr=on}} and were observed for over two hours after the largest impacts. The waves were thought to be travelling within a stable layer acting as a [[waveguide]], and some scientists thought the stable layer must lie within the hypothesised [[troposphere|tropospheric]] water cloud. However, other evidence seemed to indicate that the cometary fragments had not reached the water layer, and the waves were instead propagating within the [[stratosphere]].<ref name="Ingersoll">{{cite journal |last1=Ingersoll |first1=A. P. |date=April 1995 |title=Waves from the collisions of comet Shoemaker–Levy 9 with Jupiter |journal=Nature |volume=374 |issue= 6524|pages=706–708 |doi=10.1038/374706a0 |pmid=7715724 |last2=Kanamori |first2=H|bibcode = 1995Natur.374..706I |s2cid=4325357 }}</ref>

=== Other observations ===
[[File:SL9ImpactGalileo.jpg|thumb|250px|A sequence of [[Galileo (spacecraft)|''Galileo'']] images, taken several seconds apart, showing the appearance of the [[Fireball (meteor)|fireball]] of fragment W on the dark side of Jupiter]]

Radio observations revealed a sharp increase in [[Black body|continuum]] emission at a wavelength of {{convert|21|cm|abbr=on}} after the largest impacts, which peaked at 120% of the normal emission from the planet.<ref>{{Cite journal|last1=de Pater|first1=I|author-link=Imke de Pater|last2=Heiles|first2=C|last3=Wong|first3=M|last4=Maddalena|first4=R.|last5=Bird|first5=M.|last6=Funke|first6=O|last7=Neidhoefer|first7=J|last8=Price|first8=R.|last9=Kesteven|first9=M|last10=Calabretta|first10=M|last11=Klein|first11=M.|date=1995-06-30|title=Outburst of Jupiter's synchrotron radiation after the impact of comet Shoemaker-Levy 9|url=https://www.science.org/doi/10.1126/science.11536723|journal=Science|language=en|volume=268|issue=5219|pages=1879–1883|doi=10.1126/science.11536723|pmid=11536723|bibcode=1995Sci...268.1879D|issn=0036-8075|url-access=subscription}}</ref> This was thought to be due to [[synchrotron radiation]], caused by the injection of [[theory of relativity|relativistic]] [[electron]]s—electrons with velocities near the speed of light—into the Jovian [[magnetosphere]] by the impacts.<ref name="Olano">{{cite journal |last=Olano |first=C. A. |date=August 1999 |title= Jupiter's Synchrotron Emission Induced by the Collision of Comet Shoemaker–Levy 9 |journal=[[Astrophysics and Space Science]] |volume=266 |issue=3 |pages=347–369 |doi=10.1023/A:1002020013936 |bibcode = 1999Ap&SS.266..347O |s2cid=118876167 }}</ref>

About an hour after fragment K entered Jupiter, observers recorded [[Aurora (phenomenon)|auroral]] emission near the impact region, as well as at the [[antipodal point|antipode]] of the impact site with respect to Jupiter's strong [[magnetic field]]. The cause of these emissions was difficult to establish due to a lack of knowledge of Jupiter's internal [[magnetic field]] and of the geometry of the impact sites. One possible explanation was that upwardly accelerating [[shock wave]]s from the impact accelerated charged particles enough to cause auroral emission, a phenomenon more typically associated with fast-moving [[solar wind]] particles striking a planetary atmosphere near a [[Poles of astronomical bodies#Magnetic poles|magnetic pole]].<ref name="Bauske">{{cite journal |last1= Bauske |first1=Rainer |date=November 1999 |title=Analysis of Midlatitude Auroral Emissions Observed during the Impact of Comet Shoemaker–Levy 9 with Jupiter |journal=[[Icarus (journal)|Icarus]] |volume=142 |issue=1 |pages=106–115 |doi=10.1006/icar.1999.6198 |bibcode=1999Icar..142..106B|last2=Combi |first2=Michael R. |last3=Clarke |first3=John T. }}</ref>

Some astronomers had suggested that the impacts might have a noticeable effect on the [[Io (moon)#Interaction with Jupiter's magnetosphere|Io torus]], a [[torus]] of high-energy particles connecting Jupiter with the highly [[volcano|volcanic]] moon [[Io (moon)|Io]]. High resolution spectroscopic studies found that variations in the ion [[density]], [[rotational velocity]], and temperatures at the time of impact and afterwards were within the normal limits.<ref name="Brown">{{cite journal |last1=Brown |first1=Michael E. |author-link=Michael E. Brown |year=1995 |title=Comet Shoemaker–Levy 9: No Effect on the Io Plasma Torus |journal=Geophysical Research Letters |volume=22 |issue=3 |pages=1833–1835 |doi=10.1029/95GL00904 |last2=Moyer |first2=Elisabeth J. |last3=Bouchez |first3=Antonin H. |last4=Spinrad |first4=Hyron |bibcode=1995GeoRL..22.1833B|url=https://authors.library.caltech.edu/34616/1/95GL00904.pdf |archive-url=https://web.archive.org/web/20180718234639/https://authors.library.caltech.edu/34616/1/95GL00904.pdf |archive-date=2018-07-18 |url-status=live }}</ref>

''[[Voyager 2]]'' failed to detect anything with calculations, showing that the fireballs were just below the craft's limit of detection; no abnormal levels of UV radiation or radio signals were registered after the blast.<ref name="williamsnasa" /><ref name=Ulivi449>{{cite book |last1=Ulivi |first1=Paolo |last2=Harland |first2= David M |date=2007 |title=Robotic Exploration of the Solar System Part I: The Golden Age 1957–1982  |publisher=Springer |page=449 |isbn=9780387493268 }}</ref> ''[[Ulysses (spacecraft)|Ulysses]]'' also failed to detect any abnormal radio frequencies.<ref name=williamsnasa />

== Post-impact analysis ==
[[File:Impact site of fragment G.png|thumb|225px|A reddish, asymmetric ejecta pattern]]

{{Anchor|calculation2016-01-26}}Several models were devised to compute the density and size of Shoemaker–Levy 9. Its average density was calculated to be about {{convert|0.5|g/cm3|abbr=on}}; the breakup of a much less dense comet would not have resembled the observed string of objects. The size of the parent comet was calculated to be about {{convert|1.8|km|abbr=on}} in diameter.<ref name=Solem1995>{{cite journal|last=Solem|first=J. C.|year=1995|title=Cometary breakup calculations based on a gravitationally-bound agglomeration model: The density and size of Comet Shoemaker-Levy 9 |journal=Astronomy and Astrophysics|volume=302|issue=2|pages=596–608 |bibcode = 1995A&A...302..596S }}</ref><ref name=Solem1994>{{cite journal|last=Solem|first=J. C.|year=1994|title=Density and size of Comet Shoemaker–Levy 9 deduced from a tidal breakup model|journal=Nature|volume=370|issue=6488|pages=349–351 |bibcode = 1994Natur.370..349S |doi = 10.1038/370349a0|s2cid=4313295|url=https://zenodo.org/record/1233164}}</ref> These predictions were among the few that were actually confirmed by subsequent observation.<ref>
{{cite book
 |last1        = Noll
 |first1       = Keith S.
 |last2       = Weaver
 |first2      = Harold A.
 |last3       = Feldman
 |first3      = Paul D .
 |year        = 2006
 |title       = Proceedings of Space Telescope Science Institute Workshop, Baltimore, MD, May 9–12, 1995, IAU Colloquium 156: The Collision of Comet Shoemaker-Levy 9 and Jupiter
 |publisher   = [[Cambridge University Press]]
 |url         = http://www.cambridge.org/us/academic/subjects/astronomy/planetary-science/collision-comet-shoemaker-levy-9-and-jupiter-iau-colloquium-156
 |url-status     = dead
 |archive-url  = https://web.archive.org/web/20151124095115/http://www.cambridge.org/us/academic/subjects/astronomy/planetary-science/collision-comet-shoemaker-levy-9-and-jupiter-iau-colloquium-156
 |archive-date = November 24, 2015
 |df          = mdy-all
}}</ref>

One of the surprises of the impacts was the small amount of water revealed compared to predictions.<ref>{{cite book |title=The Planetary Scientist's Companion |last=Loders |first=Katharina |author2=Fegley, Bruce |year=1998 |publisher=[[Oxford University Press]] |isbn=978-0-19-511694-6 |page=200 |chapter-url=https://books.google.com/books?id=qTZAyOF8J4wC&q=Comet+Shoemaker-Levy+9,+water,+impact,+small+amount |chapter=Jupiter, Rings and Satellites}}</ref> Before the impact, models of Jupiter's atmosphere had indicated that the break-up of the largest fragments would occur at atmospheric pressures of anywhere from 30 [[Pascal (unit)|kilopascals]] to a few tens of [[Pascal (unit)|megapascals]] (from 0.3 to a few hundred [[bar (unit)|bar]]),<ref name="Hu">{{cite journal |last1=Hu |first1=Zhong-Wei |date=May 1996 |title=On Penetration Depth of the Shoemaker–Levy 9 Fragments into the Jovian Atmosphere |journal=Earth, Moon, and Planets |volume=73 |issue=2 |pages=147–155 |bibcode=1996EM&P...73..147H |doi=10.1007/BF00114146 |last2=Chu |first2=Yi |last3=Zhang |first3=Kai-Jun|s2cid=122382596 }}</ref> with some predictions that the comet would penetrate a layer of water and create a bluish shroud over that region of Jupiter.<ref name="Bruton1.5" />

Astronomers did not observe large amounts of water following the collisions, and later impact studies found that fragmentation and destruction of the cometary fragments in a [[meteor air burst]] probably occurred at much higher altitudes than previously expected, with even the largest fragments being destroyed when the pressure reached {{convert|250|kPa|0|abbr=on}}, well above the expected depth of the water layer. The smaller fragments were probably destroyed before they even reached the cloud layer.<ref name="Hu" />

== Longer-term effects ==
[[File:Subtle Ripples in Jupiter's Rings by Galileo PIA13893 modest.jpg|thumb|Ripples in the rings of Jupiter seen by ''Galileo'' spacecraft, caused by Shoemaker-Levy 9]]
The visible scars from the impacts could be seen on Jupiter for many months. They were extremely prominent, and observers described them as more easily visible than the [[Great Red Spot]]. A search of historical observations revealed that the spots were probably the most prominent transient features ever seen on the planet, and that although the Great Red Spot is notable for its striking color, no spots of the size and darkness of those caused by the SL9 impacts had ever been recorded before, or since.<ref name="Hockey">{{cite journal |last=Hockey |first=T.A. |year=1994 |title=The Shoemaker–Levy 9 Spots on Jupiter: Their Place in History |journal= Earth, Moon, and Planets |doi=10.1007/BF00612878 |volume=66 |issue=1 |pages=1–9 |bibcode=1994EM&P...66....1H|s2cid=121034769 }}</ref>

The impact produced many new species in the stratosphere of Jupiter. Long-lasting species are [[Water vapor|H<sub>2</sub>O]], [[Carbon monoxide|CO]], [[Carbon monosulfide|CS]] and [[Hydrogen cyanide|HCN]].<ref name=":0">{{Cite journal |last1=Rodríguez-Ovalle |first1=Pablo |last2=Fouchet |first2=Thierry |last3=Cavalié |first3=Thibault |last4=Lellouch |first4=Emmanuel |last5=Fletcher |first5=Leigh N. |last6=Harkett |first6=Jake |last7=Hue |first7=Vincent |last8=Benmahi |first8=Bilal |last9=Pater |first9=Imke de |date=2025-04-01 |title=JWST observations of exogenic species on Jupiter: HCN, H2O, and CO2 |url=https://www.aanda.org/articles/aa/full_html/2025/04/aa53575-24/aa53575-24.html |journal=Astronomy & Astrophysics |language=en |volume=696 |pages=A173 |bibcode=2025A&A...696A.173R |doi=10.1051/0004-6361/202453575 |issn=0004-6361|doi-access=free }}</ref> H<sub>2</sub>O emission was monitored between 2002 and 2019 with the [[Odin (satellite)|Odin Space Telescope]] and showed a linear decline.<ref>{{Cite journal |last1=Benmahi |first1=B. |last2=Cavalié |first2=T. |last3=Dobrijevic |first3=M. |last4=Biver |first4=N. |last5=Bermudez-Diaz |first5=K. |last6=Sandqvist |first6=Aa |last7=Lellouch |first7=E. |last8=Moreno |first8=R. |last9=Fouchet |first9=T. |last10=Hue |first10=V. |last11=Hartogh |first11=P. |last12=Billebaud |first12=F. |last13=Lecacheux |first13=A. |last14=Hjalmarson |first14=Å |last15=Frisk |first15=U. |date=2020-09-01 |title=Monitoring of the evolution of H2O vapor in the stratosphere of Jupiter over an 18-yr period with the Odin space telescope |url=https://www.aanda.org/articles/aa/full_html/2020/09/aa38188-20/aa38188-20.html |journal=Astronomy & Astrophysics |language=en |volume=641 |pages=A140 |arxiv=2007.05415 |bibcode=2020A&A...641A.140B |doi=10.1051/0004-6361/202038188 |issn=0004-6361}}</ref> Spectroscopic observers found that [[ammonia]] and [[carbon disulfide]] (CS<sub>2</sub>) persisted in the atmosphere for at least fourteen months after the collisions, with a considerable amount of ammonia being present in the stratosphere as opposed to its normal location in the troposphere.<ref name="McGrath 2">{{cite journal |last1=McGrath |first1=M.A. |date=September 1996 |title=Long-term Chemical Evolution of the Jupiter Stratosphere Following the SL9 Impacts |journal=Bulletin of the American Astronomical Society |volume=28 |page=1149 |bibcode=1996DPS....28.2241M |last2=Yelle |first2=R. V. |last3=Betremieux |first3=Y.}}</ref> CS was detected 19 years after the impact with the [[Atacama Submillimeter Telescope Experiment]] in the atmosphere of Jupiter. The CS total mass showed a 90% decrease.<ref>{{Cite journal |last1=Iino |first1=T. |last2=Ohyama |first2=H. |last3=Hirahara |first3=Y. |last4=Takahashi |first4=T. |last5=Tsukagoshi |first5=T. |date=November 22, 2016 |title=Submillimeter Observation of Jupiter's Stratospheric Composition: Detection of Carbon Monosulfide (J=7-6) 19 Years After the Cometary Impact  |journal=[[The Astronomical Journal]] |volume=152 |issue=6 |pages=179 |doi=10.3847/0004-6256/152/6/179 |arxiv=1610.02802 |bibcode=2016AJ....152..179I |doi-access=free |issn=0004-6256}}</ref>

The new species can help to reveal the processes in Jupiter’s [[aurora]]. [[Atacama Large Millimeter Array|ALMA]] detected CO and HCN. In and near the auroral region HCN was depleted. Chemical processes bonds HCN on large aurora-produced [[Aerosol|aerosols]].<ref>{{Cite journal |last1=Cavalié |first1=T. |last2=Rezac |first2=L. |last3=Moreno |first3=R. |last4=Lellouch |first4=E. |last5=Fouchet |first5=T. |last6=Benmahi |first6=B. |last7=Greathouse |first7=T. K. |last8=Sinclair |first8=J. A. |last9=Hue |first9=V. |last10=Hartogh |first10=P. |last11=Dobrijevic |first11=M. |last12=Carrasco |first12=N. |last13=Perrin |first13=Z. |date=September 2023 |title=Evidence for auroral influence on Jupiter's nitrogen and oxygen chemistry revealed by ALMA |url=https://ui.adsabs.harvard.edu/abs/2023NatAs...7.1048C/abstract |journal=Nature Astronomy |language=en |volume=7 |issue=9 |pages=1048–1055 |arxiv=2407.07385 |bibcode=2023NatAs...7.1048C |doi=10.1038/s41550-023-02016-7 |issn=2397-3366}}</ref> [[James Webb Space Telescope|JWST]] observations from December 2022 detected an increase of H<sub>2</sub>O in the south polar region, while [[Carbon dioxide|CO<sub>2</sub>]] is depleted. This is seen as an exchange of [[oxygen]] between the two molecules in the southern auroral region. HCN is also depleted towards the south polar region.<ref name=":0" />

Atmospheric temperatures dropped to normal levels much more quickly at the larger impact sites than at the smaller sites: at the larger impact sites, temperatures were elevated over a region {{convert|15000|to|20000|km|abbr=on}} wide, but dropped back to normal levels within a week of the impact. At smaller sites, temperatures 10 K (10 °C; 18 °F) higher than the surroundings persisted for almost two weeks.<ref name="Bézard">{{cite journal |last=Bézard |first=B. |date=October 1997 |title=Long-term Response of Jupiter's Thermal Structure to the SL9 Impacts |journal=Planetary and Space Science |volume=45 |issue=10 |pages=1251–1271 |doi=10.1016/S0032-0633(97)00068-8 |bibcode=1997P&SS...45.1251B}}</ref> Global stratospheric temperatures rose immediately after the impacts, then fell to below pre-impact temperatures 2–3&nbsp;weeks afterwards, before rising slowly to normal temperatures.<ref name="Moreno">{{cite journal |last1= Moreno|first1=R.|date=June 2001 |title= Jovian Stratospheric Temperature during the Two Months Following the Impacts of Comet Shoemaker–Levy 9|journal=Planetary and Space Science |volume=49 |issue=5 |pages=473–486 |doi=10.1016/S0032-0633(00)00139-2 |bibcode=2001P&SS...49..473M |last2= Marten |first2= A |last3= Biraud |first3= Y |last4= Bézard |first4= B |last5= Lellouch |first5= E |last6= Paubert |first6= G |last7= Wild |first7= W}}</ref>

Comet Shoemaker-Levy 9 also caused ripples in the [[Rings of Jupiter|faint ring system of Jupiter]], which were first observed by ''[[Galileo (spacecraft)|Galileo]]''. 13 years later, the ''[[New Horizons]]'' spacecraft en route to [[Pluto]] also observed ripples, suggesting that subsequent events may have also tilted the rings.<ref>{{Cite journal |last1=R. |first1=Showalter, Mark |last2=M. |first2=Hedman, Matthew |last3=A. |first3=Burns, Joseph |date=May 2011 |title=The Impact of Comet Shoemaker-Levy 9 Sends Ripples Through the Rings of Jupiter |url=https://ui.adsabs.harvard.edu/abs/2011Sci...332..711S/abstract |journal=Science |language=en |volume=332 |issue=6030 |pages=711–713 |bibcode=2011Sci...332..711S |doi=10.1126/science.1202241 |pmid=21454755 |issn=0036-8075 |archive-url=https://web.archive.org/web/20240906175924/https://ui.adsabs.harvard.edu/abs/2011Sci...332..711S/abstract |archive-date=September 6, 2024 |access-date=May 14, 2025 |url-status=live }}</ref> Additionally it is predicted that the comet could have formed a new ring around Jupiter.<ref>{{Cite journal |last=Horanyi |first=Mihaly |date=December 2024 |title=Did SL9 Leave Behind a New Jovian Ring? |url=https://ui.adsabs.harvard.edu/abs/2024AGUFMNH43D2442H/abstract |journal=AGU Fall Meeting 2024 |issue=2442 |bibcode=2024AGUFMNH43D2442H}}</ref>

== 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 |date=July 21, 2009 |title=Mystery impact leaves Earth-size mark on Jupiter |url=https://edition.cnn.com/2009/TECH/space/07/21/jupiter.nasa.meteor.scar/ |website=[[CNN]]}}</ref>

== 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>

== See also ==
* [[List of Jupiter events]]
* [[Impact events on Jupiter]]
* [[Atmosphere of Jupiter]]
* [[73P/Schwassmann–Wachmann]], a near-Earth comet in the process of disintegrating

== References ==

=== Notes ===
{{Reflist|30em}}

=== Bibliography ===
* {{Cite book |last1=Chodas |first1=Paul W. |title=The orbital motion and impact circumstances of Comet Shoemaker-Levy 9 |last2=Yeomans |first2=Donald K. |date=1996 |publisher=[[Cambridge University Press]] |isbn=978-0-521-56192-1 |editor-last=Noll |editor-first=Keith S. |pages=1–30 |doi=10.1017/cbo9780511525056.003 |editor-last2=Weaver |editor-first2=Harold A. |editor-last3=Feldman |editor-first3=Paul D.}}
* {{Cite web |last=Chodas |first=P. W. |date=2002 |title=Communication of Orbital Elements to Selden E. Ball, Jr. |url=https://www.classe.cornell.edu/~seb/celestia/elements_1993e_.txt |access-date=February 21, 2006 |website=[[Cornell Laboratory for Accelerator-based Sciences and Education]] |publisher=[[Cornell University]]}}

== External links ==
{{Commons category|Comet Shoemaker-Levy 9}}
{{Spoken Wikipedia|Comet_Shoemaker-Levy_9.ogg|date=2006-04-14}}
* [https://www2.jpl.nasa.gov/sl9/ First Comet Shoemaker-Levy 9 website that collected  photos submitted from observatories around the world and from Galileo spacecraft], curated by Ron Baalke, Jet Propulsion Laboratory software engineer
* [http://www.midnightkite.com/sl9.html Comet Shoemaker–Levy 9 FAQ]
* [https://web.archive.org/web/20020603124548/http://www.seds.org/sl9/sl9.html Comet Shoemaker–Levy 9 Photo Gallery]
* [https://web.archive.org/web/20130723035832/http://rack1.ul.cs.cmu.edu/jupiterimpact/ Downloadable gif Animation showing time course of impact and size relative to earthsize]
* [http://www.cv.nrao.edu/~pmurphy/patsl9.html Comet Shoemaker-Levy 9] Dan Bruton, [[Texas A&M University]]
* [https://web.archive.org/web/20180303143750/https://apod.nasa.gov/apod/ap001105.html Jupiter Swallows Comet Shoemaker Levy 9] APOD: November 5, 2000
* [http://www2.jpl.nasa.gov/sl9/sl9.html Comet Shoemaker–Levy Collision with Jupiter]
* [https://web.archive.org/web/20130219011148/http://nssdc.gsfc.nasa.gov/planetary/comet.html National Space Science Data Center information]
* [http://www.orbitsimulator.com/gravity/articles/sl9.html Simulation of the orbit of SL-9 showing the passage that fragmented the comet and the collision 2 years later]
* [http://universesandbox.com/ Interactive space simulator that includes accurate 3D simulation of the Shoemaker Levy 9 collision]
* [https://pdssbn.astro.umd.edu/data_sb/missions/sl9/index.shtml ''Shoemaker-Levy 9'' Jupiter Impact Observing Campaign Archive] at the NASA Planetary Data System, Small Bodies Node

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{{DEFAULTSORT:Shoemaker-Levy, 1993 F2}}
[[Category:Destroyed comets]]
[[Category:Discoveries by Carolyn S. Shoemaker]]
[[Category:Discoveries by Eugene Merle Shoemaker]]
[[Category:Discoveries by David H. Levy|1993 F2]]
[[Category:Collision]]
[[Category:Jupiter impact events]]
[[Category:1994 in science]]
[[Category:Astronomical objects discovered in 1993|19930324]]
[[Category:Predicted impact events]]