Mission Information
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MISSION_NAME |
COMET SL9/JUPITER COLLISION
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MISSION_ALIAS |
COMET IMPACT 94
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MISSION_START_DATE |
1993-01-01T12:00:00.000Z
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MISSION_STOP_DATE |
1996-01-01T12:00:00.000Z
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MISSION_DESCRIPTION |
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
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MISSION_OBJECTIVES_SUMMARY |
Mission Objectives Overview
===========================
The first part of Jupiter that SL9 encountered was the Jovian
magnetosphere. Some radio and auroral activity were indeed observed
during the SL9 impacts. The optical flashes from the bolide and
fireball phases were far more difficult to detect than predicted.
It was not immediately obvious how deep the large fragments of SL9
penetrated, or how much material was dredged up from Jupiter. The
larger-than-expected plumes that were observed may have merely been
the blow off of material resulting from the shallow splash of an
extended cloud of debris. The slow-moving atmospheric gravity waves
were, in fact, seen. Finally, the dust particles from SL9 may after
several years settle into a ring around Jupiter; sensors on board
Galileo may detect such cometary dust.
|
REFERENCE_DESCRIPTION |
AHearn, M., and L. A. McFadden, Fact Sheet: Comet P/Shoemaker-Levy 9 and
Jupiter, private communication, 1994.
Chodas, P. and D. Yeomans, The Collision of Comet Shoemaker-Levy 9 and Jupiter,
editors K. Noll, H. Weaver, and P. Feldman, IAU Colloquium 156, ISBN
0-521-56192-2, Cambridge, United Kingdom, 1996.
Horrocks, K., and M. AHearn, European SL9/ Jupiter Workshop, editors R.
West and H. Boehnhardt, ESO Conference and Workshop Proceedings #52, ISBN
3-923524-55-2, Garching, Germany, 1995.
Newburn, R., Periodic Comet Shoemaker-Levy 9 Collides with Jupiter, JPL
400-520, 3/94, Pasadena, CA, 1994.
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