Editing Comet Shoemaker–Levy 9 (section)

== 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}}</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 />