Mission Overview
    ================
    Significance
    ------------
      The impact of comet Shoemaker-Levy 9 onto Jupiter represented the
      first time in human history that people have discovered a body in
      the sky and been able to predict its impact on a planet more than
      seconds in advance.  The impact delivered more energy to Jupiter
      than the largest nuclear warheads ever built, and up to a
      significant percentage of the energy delivered by the impact which
      is generally thought to have caused the extinction of the dinosaurs
      on Earth, roughly 65 million years ago.
 
      History
      -------
      The comet, the ninth short-period comet discovered by Gene and
      Carolyn Shoemaker and David Levy, was first identified on a
      photograph taken on the night of 24 March 1993 with the 0.4-meter
      Schmidt telescope at Mt. Palomar.  On the original image it appeared
      'squashed'.  Subsequent photographs at a larger scale taken by Jim
      Scotti with the Spacewatch telescope on Kitt Peak showed that the
      comet was split into many separate fragments.  Before the end of
      March it was realized that the comet had made a very close approach
      to Jupiter in mid-1992 and at the beginning of April, after
      sufficient observations had been made to determine the orbit more
      reliably, Brian Marsden found that the comet is in orbit around
      Jupiter.  By late May it appeared that the comet was likely to
      impact Jupiter in 1994.  Since then, the comet has been the subject
      of intensive study.  Searches of archival photographs have
      identified pre-discovery images of the comet from earlier in March
      1993 but searches for even earlier images have been unsuccessful.
 
      Cometary Orbit
      --------------
      According to the most recent computations, the comet passed less
      than 1/3 of a Jovian radius above the clouds of Jupiter late on 7
      July 1992 (UT).  The individual fragments separated from each other
      1 1/2 hours after closest approach to Jupiter and they are all in
      orbit around Jupiter with an orbital period of about two years.
      Calculations of the orbit prior to 7 July 1992 are very uncertain
      but it seems very likely that the comet was previously in orbit
      around Jupiter for two decades or more.  Because the orbit takes the
      comet nearly 1/3 of an astronomical unit (30 million miles) from
      Jupiter, the sun causes significant changes in the orbit.  Thus,
      when the comet again came close to Jupiter in 1994 it actually
      impacted the planet, moving almost due northward at 60 km/sec aimed
      at a point only halfway from the center of Jupiter to the visible
      clouds.
 
      The 23 identified fragments all hit Jupiter in the southern
      hemisphere, at latitudes near 45 S, between 16 and 22 July 1994,
      approaching the atmosphere at an angle roughly 45 deg from the
      vertical.  The times of the impacts were known to within a few hours
      but observations in early 1994 significantly improved the precision
      of the predictions.  The impacts happened on the back side of
      Jupiter as seen from Earth in an area that was also in darkness.
      This area was close to the limb of Jupiter and was carried by
      Jupiter's rotation to the front, illuminated side less than half an
      hour after the impact.  The grains ahead of and behind the comet
      impacted Jupiter over a period of four months, centered on the time
      of the impacts of the major fragments.  The grains in the tail of
      the comet passed behind Jupiter and remain in orbit around the
      planet.
 
      The Nature of the Comet
      -----------------------
      The exact number of large fragments is not certain since the best
      images show hints that some of the larger fragments were multiple.
      At least 23 major fragments were identified.  No observations are
      capable of resolving the individual fragments to show the solid
      nuclei.  Images with the Hubble Space Telescope suggested that there
      were discrete, solid nuclei in each of the largest fragments which,
      although not spatially resolved, produce a single, bright pixel that
      stood out above the surrounding coma of grains.  Reasonable
      assumptions about the spatial distribution of the grains and about
      the reflectivity of the nuclei implied sizes of 2 to 4 km (diameter)
      for each of the 11 brightest nuclei.  Because of the uncertainties
      in these assumptions, the actual sizes were very uncertain.
 
      No outgassing was detected from the comet.  The dust distribution
      suggests that the material ahead of and behind the major fragments
      in the orbit were likely large particles from the size of sand up to
      boulders.  The particles in the tail are very small, not much larger
      than the wavelength of light.  The brightnesses of the major
      fragments were observed to change by factors up to 1.7 between March
      and July 1993, although some became brighter while others became
      fainter.
 
      Summary of impact times, impact locations, and impact geometries
      ----------------------------------------------------------------
      Published estimates of the impact times and locations of the
      fragments of SL9 are given below (Table 5 in Chodas, P.W. and
      Yeomans, D.K.(1996) [CHODAS&YEOMANS1996]).  Impact was defined to
      occur at the 100mbar level of Jupiter's atmosphere.  The impact for
      all fragments except J and M are based on independent orbit
      solutions given by Chodas and Yeomans (1996) [CHODAS&YEOMANS1996].
      The estimates for the 'lost' fragments J and M were obtained by
      applying the tidal disruption model to the orbit for fragment Ql and
      matching the astrometry of these two fragments relative to Ql.  The
      third column of the table contains the final pre-impact prediction
      for each of the fragments as distributed electronically by the UMd
      e-mail exploder.  The fourth column lists the final best estimates,
      which were inferred directly from impact phenomena for 16 fragments,
      and computed from the orbit solutions for the rest.  All times are
      as viewed from the Earth, and therefore include the light travel
      time.  The impact time uncertainties are rough estimates which
      indicate a confidence level in the accepted time; they are not
      formal 1-sigma uncertainties.  The impact latitude is jovicentric,
      while the longitude is System III, measured westwards on the
      planet.  The meridian angle is the jovicentric longitude of the
      impact point measured from the midnight meridian towards the morning
      terminator.  At the latitude of the impacts, the limb as viewed from
      the Earth was at meridian angle 76 deg, and the terminator was at
      meridian angle 87 deg.  The final column gives the angular distance
      of the impacts behind the limb.
 
  Event         Impact Time (UTC)         Impact Location Merid. Ang. Dist.
         -------------------------------  --------------- Angle Behind Limb
        Date   Predicted  Accepted   +/-    Lat.    Lon.
       (July)   h m s      h m s     (s)   (deg)    (deg) (deg)    (deg)
 
    A    16    19:59:40   20:10:40    60   -43.35    184   65.40    7.7
    B    17    02:54:13   02:50:00   180   -43.22     67   63.92    8.8
    C    17    07:02:14   07:10:50    60   -43.47    222   66.14    7.1
    D    17    11:47:00   11:52:30    60   -43.53     33   66.16    7.1
    E    17    15:05:31   15:11:40   120   -43.54    153   66.40    6.9
    F    18    00:29:21   00:35:45   300   -43.68    135   65.30    7.7
    G    18    07:28:32   07:33:33     3   -43.66     26   67.09    6.4
    H    18    19:25:53   19:31:59     1   -43.79     99   67.47    6.1
    J    19    02:40      01:35     3600   -43.75   ~316   68.05   ~6
    K    19    10:18:32   10:24:17     2   -43.86    278   68.32    5.5
    L    19    22:08:53   22:16:49     1   -43.96    348   68.86    5.1
    M    20    05:45      06:00      600   -43.93   ~264   69.25   ~5
    N    20    10:20:02   10:29:20     2   -44.31     71   68.68    5.1
    P2   20    15:16:20   15:21:11   300   -44.69    249   67.58    5.8
    P1   20    16:30      16:32:35   800   -45.02   ~293   65.96    6.9
    Q2   20    19:47:11   19:44:00    60   -44.32     46   69.26    4.7
    Q1   20    20:04:09   20:13:53     1   -44.00     63   69.85    4.3
    R    21    05:28:50   05:34:57    10   -44.10     42   70.21    4.1
    S    21    15:12:49   15:16:30    60   -44.22     33   70.34    4.0
    T    21    18:03:45   18:09:56   300   -45.01    141   67.73    5.7
    U    21    21:48:30   22:00:02   300   -44.48    278   69.54    4.5
    V    22    04:16:53   04:23:20    60   -44.47    149   69.96    4.2
    W    22    17:59:45   08:06:16     1   -44.13    283   71.19    3.4
 
      Contributing Observatories that Recorded the Event
      --------------------------------------------------
      As was expected, nearly every observatory in the world was observing
      events associated with the impact.  These observatories included
      several Earth-orbiting telescopes (Hubble Space Telescope,
      International Ultraviolet Explorer, Extreme Ultraviolet Explorer,
      ROSAT) and several interplanetary spacecraft (Galileo, Ulysses,
      Voyager 2).  A list follows:
 
      Observatory(Abbr)      Name and Location
      SPIREX                (South Pole Infra-Red Explorer  Antarctica)
 
      AAT                   (Anglo-Australian Telescope  Australia)
      ANU                   (Australian National University  Australia)
      Australia Telescope   (Australia Telescope  Australia)
      Charters Towers       (Charters Towers  Australia)
      MOST                  (Molonglo Observatory Synthesis Telescope
                             Australia)
      Mt. Singleton         (Mt. Singleton  Australia)
      MSSSO                 (Mount Stromlo and Siding Spring Observatory
                             Australia)
      Perth                 (Perth Observatory  Australia)
 
      Pico-dos-Dias         (Pico-dos-Dias Observatory  Brazil)
      University of Sao Paulo  (University of Sao Paulo  Brazil)
 
      Belogradchik          (Belogradchik Observatory  Bulgaria)
      Rozhen                (Rozhen Observatory  Bulgaria)
 
      CTIO                  (Cerro Tololo Interamerican Observatory  Chile)
      ESO                   (European Southern Observatory  Chile)
      Las Campanas          (Las Campanas Observatory  Chile)
      Maipu                 (Maipu Radio Astronomy Observatory  Chile)
 
      Beijing               (Beijing Astronomical Observatory  China)
 
      University of Cambridge  (University of Cambridge Observatory
                                England)
 
      Nancay                (Nancay Radio Telescope  France)
      Pic du Midi           (Pic du Midi Observatory  France)
 
      ORT                   (Ooty Radio Telescope  India)
      Vainu Bappu           (Vainu Bappu Observatory  India)
 
      CAO                   (Catania Astrophysical Observatory  Italy)
      Legnano               (Legnano Observatory  Italy)
      Space Geodesy Center  (Italian Space Agency's Space Geodesy Center
                             Italy)
      Specola Vaticana      (Vatican Observatory  Italy)
      Gornergrat North Obs  (Italian TIRGO telescope)
 
      Nishi-Harima          (Nishi-Harima Astronomical Observatory  Japan)
      Okayama               (Okayama Astrophysical Observatory  Japan)
      Okinawa               (Okinawa Observatory  Japan)
 
      Assy                  (Assy Observatory  Kazakhstan)
 
      Bohyunsan             (Bohyunsan Observatory   Korea)
      Daeduk                (Daeduk Observatory  Korea)
      Kyunghee University   (Kyunghee University Observatory  Korea)
      Sobaeksan             (Sobaeksan Observatory  Korea)
 
      San Pedro Martir      (San Pedro Martir Observatory  Mexico)
 
      Mt. John              (Mt. John University Observatory   New Zealand)
 
      SAO                   (Special Astrophysical Observatory  Russia)
 
      Calar Alto            (Calar Alto Observatory  Spain)
      IRAM                  (IRAM  Spain)
      La Palma              (La Palma  Spain)
      Sierra Nevada         (Sierra Nevada Observatory  Spain)
      Teide                 (Teide Observatory  Spain)
 
      SAAO                  (South African Astronomical Observatory
                             South Africa)
 
      National Central University  (National Central University Observatory
                                    Taiwan)
 
      KPNO                  (Kitt Peak National Observatory  Arizona)
      Lowell                (Lowell Observatory  Arizona)
      Mt. Lemmon            (Mt. Lemmon Observatory  Arizona)
      Steward               (Steward Observatory  Arizona)
      AST                   (Airborne Surveillance Testbed)
      Goldstone             (Goldstone Deep Space Communication Complex
                             California)
      KAO                   (Kuiper Airborne Observatory  California)
      Lick                  (Lick Observatory  California)
      Mt. Wilson            (Mt. Wilson Observatory  California)
      OVRO                  (Owens Valley Radio Observatory  California)
      Palomar               (Palomar Observatory  California)
      TMO                   (Table Mountain Observatory  California)
      VLA                   (NRAO Very Large Array New Mexico)
      Mt. Evans-Womble      (Mt. Evans-Womble Observatory  Colorado)
      University of Colorado   (University of Colorado  Colorado)
      CSO                   (Caltech Submillimeter Observatory  Hawaii)
      University of Florida (University of Florida Radio Observatory
                             Florida)
      CFHT                  (Canada-France-Hawaii Telescope  Hawaii)
      IRTF                  (Infrared Telescope Facility  Hawaii)
      JCMT                  (James Clerk Maxwell Telescope  Hawaii)
      Keck                  (W. M. Keck Observatory   Hawaii)
      UKIRT                 (United Kingdom Infrared Telescope  Hawaii)
      University of Hawaii  (Univ. of Hawaii Planetary Patrol Telescope
                             Hawaii)
      Harvard College       (Harvard College Observatory  Massachusetts)
      Whately               (Whately Observatory  Massachusetts)
      APO                   (Apache Point Observatory  New Mexico)
      NSO                   (National Solar Observatory  New Mexico)
      SOR                   (Starfire Optical Range  New Mexico)
      Custer                (Custer Observatory  New York)
      Mees                  (C.E. Kenneth Mees Observatory  New York)
      Wilmot                (University of Rochester Wilmot Observatory
                             New York)
      McDonald              (McDonald Observatory  Texas)
      Texas A&M             (Texas A&M Observatory  Texas)
      USNO                  (U. S. Naval Observatory  Washington D. C.)
      Yerkes                (Yerkes Observatory  Wisconsin)
      WIRO                  (Wyoming Infrared Observatory  Wyoming)
 
      Llano del Hato        (Llano del Hato Observatory  Venezuela)
 
      Santa Clara University  (Santa Clara University)
      IJW Decametric Wavelength Network

PDS4 note: awaiting LID references to facilities and telescopes
- QUEENSLAND AUSTRALIA PORTABLE C-14
- CTIO PLANETARY PATROL TELESCOPE
- EUROPEAN SOUTHERN OBSERVATORY
- NASA INFRARED TELESCOPE FACILITY
- LICK OBSERVATORY ANNA L. NICKEL 1-METER TELESCOPE
- MAUNA KEA OBSERVATORY PLANETARY PATROL TELESCOPE
- MOUNT STROMLO SIDING SPRING OBSERVATORY
- MT. SINGLETON C14 PORTABLE TELESCOPE
- OKAYAMA ASTROPHYSICAL OBSERVATORY
- REUNION ISLAND PORTABLE C-14