1043 lines
56 KiB
Plaintext
1043 lines
56 KiB
Plaintext
From village.com!news.kei.com!yeshua.marcam.com!usc!elroy.jpl.nasa.gov!netline-fddi.jpl.nasa.gov!marsupial.jpl.nasa.gov!not-for-mail Fri Jun 17 07:52:16 1994
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Path: village.com!news.kei.com!yeshua.marcam.com!usc!elroy.jpl.nasa.gov!netline-fddi.jpl.nasa.gov!marsupial.jpl.nasa.gov!not-for-mail
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From: kdq@marsupial.jpl.nasa.gov (Kevin D. Quitt)
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Newsgroups: sci.skeptic
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Subject: Re: Jupiter, Comets, and calamaty
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Date: 16 Jun 1994 20:07:33 -0700
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Organization: Jet Propellor Laboratory
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Lines: 1029
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Message-ID: <2tr41l$r0b@marsupial.jpl.nasa.gov>
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References: <2tnv4l$dku@tadpole.fc.hp.com>
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NNTP-Posting-Host: marsupial.jpl.nasa.gov
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Thus wrote antonsen@cnd.hp.com (Tim Antonsen)
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>Just curious if anybody has heard any prophecies about Jupiter's pending
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>encounter with cometary fragments, slated for July 16. I can imagine people
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>foretelling the birth of a binary star system, for example: Sol/Jupiter.
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Not prophecy, but useful:
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Newsgroups: jpl.shoemaker-levy
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Subject: Comet/Jupiter Collision FAQ - 6/14/94
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* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
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Frequently Asked Questions about
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the Collision of Comet Shoemaker-Levy 9 with Jupiter
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Last Updated 14-Jun-1994
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32 Days to Impact
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The following is a list of answers to frequently asked questions
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concerning the collision of comet Shoemaker-Levy 9 with Jupiter. Thanks
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to all those who have contributed. Contact Dan Bruton (astro@tamu.edu)
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or John Harper (jharper@tamu.edu) with comments, additions, corrections,
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etc. A PostScript version and updates of this FAQ list are available via
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anonymous ftp to tamsun.tamu.edu (128.194.15.32) in the /pub/comet
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directory. To subscribe to the "Comet/Jupiter Collision Mailing List",
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send mail to listproc@seds.lpl.arizona.edu (no subject) with the message:
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SUBSCRIBE SL9 Firstname Lastname.
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RECENT CHANGES TO THIS FAQ LIST
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Question 1.1: Limb Crossing Times
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Question 1.3: HST March images
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Question 1.4: More predictions
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Question 2.1: Updated impact times and impact locations
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Question 2.3: Galilean satellite eclipses
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Question 2.4: Updated orbital parameters of the comet
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Question 2.5: Images of crater chains
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Question 2.10: Mail access to files
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REFERENCES: New Journal Articles
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GENERAL QUESTIONS
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Q1.1: Is it true that a comet will collide with Jupiter in July 1994?
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Q1.2: Who are Shoemaker and Levy?
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Q1.3: Where can I find a GIF image of this comet?
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Q1.4: What will be the effects of the collision?
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Q1.5: Can I see the effects in my telescope?
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SPECIFICS
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Q2.1: What are the impact times and impact locations?
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Q2.2: Can the collisions be observed with radio telescopes?
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Q2.3: Will light from the explosions be reflected by any moons?
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Q2.4: What are the orbital parameters of the comet?
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Q2.5: Why did the comet break apart?
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Q2.6: What are the sizes of the fragments?
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Q2.7: How long is the fragment train?
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Q2.8: Will Hubble, Galileo, etc. be able to observe the collisions?
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Q2.9: To whom can I report my observations?
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Q2.10: Where can I find more information?
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REFERENCES
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ACKNOWLEDGMENTS
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* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
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GENERAL QUESTIONS
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Q1.1: Is it true that a comet will collide with Jupiter in July 1994?
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Yes, the shattered comet Shoemaker-Levy 9 (1993e) is expected to
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collide with Jupiter over a 5.6 day period in July 1994. The first of 21
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comet fragments is expected to hit Jupiter on July 16, 1994 and the last on
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July 22, 1994. The 21 major fragments are denoted A through W in order of
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impact, with letters I and O not used. All of the comet fragments will hit
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on the dark farside of Jupiter. The probability that all of the comet
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fragments will hit Jupiter is greater that 99.9%. The probability that any
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fragment will impact on the near side as viewed from the Earth is < 0.01%.
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The impact of the center of the comet train is predicted to occur at a
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Jupiter latitude of about -44 degrees at a point about 67 degrees east
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(toward the sunrise terminator) from the midnight meridian. These impact
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point estimates from Chodas and Yeomans are only 5 to 9 degrees behind the
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limb of Jupiter as seen from Earth. About 8 to 18 minutes after each
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fragment hits, the impact points will rotate past the limb. The impact
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sites of the later fragments are closer to the limb and will therefore
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rotate into view sooner after impact. After these points cross the limb it
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will take another 18 minutes before they cross the morning terminator into
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sunlight.
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Q1.2: Who are Shoemaker and Levy?
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Eugene and Carolyn Shoemaker and David H. Levy found the 13.8 magnitude
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comet on photographic plates taken on March 24, 1993. The photographs were
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taken at Palomar Mountain in Southern California with a 0.46 meter Schmidt
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camera and were examined using a stereomicroscope to reveal the comet [2,14].
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James V. Scotti confirmed their discovery with the Spacewatch Telescope at
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Kitt Peak in Arizona. See [11] for more information about the discovery.
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Q1.3: Where can I find a GIF image of this comet?
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GIF images can be obtained from SEDS.LPL.Arizona.EDU (128.196.64.66)
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in the /pub/astro/SL9/images directory. Below is a list of the images at
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this site. The files are listed here in reverse chronological order:
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Comet1993eA.gif March HST image of SL9 comet train
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Comet1993eB.gif Time comparison image of SL9 comet fragment
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sl90216.gif February 16, 1994 Image from Kitt Peak (J. Scotti)
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wfpclevy.gif Photo Montage of January 24-27 Imaging of SL9 from HST
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sl9hst.gif Post-fix HST Mosaic of SL9 (Jan. 24-27)
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sl90121.gif January 21, 1994 Image from Kitt Peak (R. Jedicke)
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sl9compl.gif Six month comparison image of SL9
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1993eha.gif View of the comet from HST
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1993ehb.gif From HST, focused on the center of the train of fragments
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1993esw.gif Ground-based view of the comet
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sl03302b.gif March 30, 1993 Image from Kitt Peak (J. Scotti)
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sl9_930330.gif March 30, 1993 image of SL9, Spacewatch, J. Scotti
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sl9w_930328.gif March 28, 1993 image of SL9
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shoelevy.gif An early GIF image of SL9
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The following is a list of other collision related GIF graphics and
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MPEG animations that are also available at SEDS.LPL.Arizona.EDU:
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gipul.gif Gipul Catena crater chain on Jupiter's moon, Callisto
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chain.gif Crater Chain on Jupiter's Moon, Callisto
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orbtrain.gif SL9's orbit showing the length of the train
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schematic2.gif Diagram of fragment positions as seen from HST; Mar'94
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schematic1.gif Diagram of fragment positions as seen from HST; Jan'94
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approach.gif View of last 18 hours of trajectory, from Earth
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earthview.gif Full-disk view from Earth
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earthviewzoom.gif Close-up view from Earth
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vgr2view.gif Full-disk view from Voyager 2
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vgr2viewzoom.gif Close-up view of impact sites from direction of Voyager 2
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galview.gif View from Galileo
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ulysview.gif View from Ulysses
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poleview.gif View from beneath Jupiter
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orbjupplane.gif SL9's orbit projected into Jupiter's orbit plane
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orbsun.gif SL9's orbit as seen from the Sun
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earthjup.gif Jupiter-Facing Hemispheres of Earth at Impact Times of SL9
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impact.gif Graph of impact times with moon eclipses
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index.gif Mosaic of some of the images in this directory
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mitwave1.gif Frame from MIT Flow Visualization Lab. Simulation
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mitwave2.gif Frame from MIT Flow Visualization Lab. Simulation
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mitwave.mpg MIT Flow Visualization Lab. Simulation Animation
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vidjv.mpg Animation of SL9 entering Jupiter's Atmosphere
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visejz.mpg Animation of explosion produced by SL9 entering Jupiter
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sl9rend.gif Rendering 3 views of comet-Jupiter collision
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sl9rend1.gif Larger rendering comet-Jupiter from Earth
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sl9rend2.gif Larger rendering comet-Jupiter from Voyager 2
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sl9rend3.gif Larger rendering comet-Jupiter from south pole
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Q1.4: What will be the effects of the collision?
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As seen from the Earth, the fragments will disappear behind the limb of
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Jupiter only 5 to 15 seconds before impact. The later fragments will be
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visible closer to impact. Fragment W will disappear only 5 seconds before
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impact, at an altitude of only about 200 km above the 1-bar pressure level:
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it may well start its bolide phase while still in view. Furthermore, any
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sufficiently dense post-impact plume will have to rise only a few hundred
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kilometers to be visible from Earth.
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Simulations by Mark Boslough and others indicate that when the fireball
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resulting from an impact cools it will form a debris cloud that will rise
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hundreds of kilometers above the Jovian cloudtops, and will enter sunlight
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within minutes of the impact. The arrival time of this giant cloud into
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sunlight would provide data on its trajectory, which in turn would help us
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know how big the comet fragment was. It is possible that it would be big
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(bright) enough to be seen by amateurs [42,43]. Mark Boslough of Sandia
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National Laboratories also states that the probability is very high that
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these effects will be visible for some of the later impacts (e.g. W and R,
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visible from Hawaii, S, visible from India and the far East, Q1 and Q2,
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visible from Africa, parts of eastern Europe and the Middle East, L, Brazil
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and West Africa, K, South Pacific and Australia, and maybe even V, on the
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final night, visible in the Western half of the U.S.). Observers in these
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locations are encouraged to anticipate the possibility of seeing the fireball
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within tens of seconds after the impact, and a few minutes later after it has
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cooled, condensed, and entered the sunlight.
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Jupiter will be about 770 million kilometers (480,000,000 miles) from
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Earth, so it will be difficult to see the effects from Earth. Also,
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the comet fragments will not effect Jupiter as a whole very much. It will
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be like sticking 21 needles into an apple: "Locally, each needle does
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significant damage but the whole apple isn't really modified very much." [35].
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The energy deposited by the comet fragments fall well short of the energy
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required to set off sustained thermonuclear fusion. Jupiter would have to
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be more than 10 times more massive to sustain a fusion reaction.
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Each comet fragment will enter the atmosphere at a speed of 130,000 mph
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(60 km/s). At an altitude of 100 km above the visible cloud decks,
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aerodynamic forces will overwhelm the material strength of the comet,
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beginning to squeeze it and tear it apart. Five seconds after entry, the
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comet fragment will deposit its kinetic energy of around 10^28 ergs
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(equivalent to around 200,000 megatons of TNT) at 100-150 km below the
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cloud layer [19]. Bigger fragments will have more energy and go deeper.
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The hot (30,000 K) gas resulting from the stopped comet will explode,
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forming a fireball similar to a nuclear explosion, but much larger.
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The visible fireball may only rise 100 km or so above the cloudtops.
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Above that height the density may drop so that it will become transparent.
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The fireball material will continue to rise, reaching a height of perhaps
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1000 km before falling back down to 300 km. The fireball will spread out
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over the top of the stratosphere to a radius of 2000-3000 km from the point
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of impact (or so the preliminary calculations say). The top of the resulting
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shock wave will accelerate up out of the Jovian atmosphere in less than two
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minutes, while the fireball will be as bright as the entire sunlit surface of
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Jupiter for around 45 sec [18]. The fireball will be somewhat red, with a
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characteristic temperature of 2000 K - 4000 K (redder than the sun, which is
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5800 K). Virtually all of the shocked cometary material will rise behind the
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shock wave, leaving the Jovian atmosphere and then splashing back down on top
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of the stratosphere at an altitude of 300 km above the clouds [unpublished
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simulations by Mac Low & Zahnle]. Not much mass is involved in this splash,
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so it will not be directly observable. The splash will be heavily enriched
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with cometary volatiles such as water or ammonia, and so may contribute to
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significant high hazes.
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Meanwhile, the downward moving shock wave will heat the local clouds,
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causing them to buoyantly rise up into the stratosphere. This will allow
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spectroscopists to attempt to directly study cloud material, a unique
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opportunity to confirm theories of the composition of the Jovian clouds.
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Furthermore, the downward moving shock may drive seismic waves (similar to
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those from terrestrial earthquakes) that might be detected over much of the
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planet by infrared telescopes in the first hour or two after each impact.
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The strength of these two effects remains a topic of research. The
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disturbance of the atmosphere will drive internal gravity waves ("ripples in
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a pond") outwards. Over the days following the impact, these waves will
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travel over much of the planet, yielding information on the structure of
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the atmosphere if they can be observed (as yet an open question).
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The "wings" of the comet will interact with the planet before and after
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the collision of the major fragments. The so-called "wings" are defined to
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be the distinct boundary along the lines extending in both directions from
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the line of the major fragments; some call these 'trails'. Sekanina, Chodas
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and Yeomans have shown that the trails consist of larger debris, not dust:
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5-cm rock-sized material and bigger (boulder-sized and building-sized).
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Dust gets swept back above (north) of the trail-fragment line due to solar
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radiation pressure. The tails emanating from the major fragments consist of
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dust being swept in this manner. Only the small portion of the eastern
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debris trail nearest the main fragments will actually impact Jupiter,
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according to the model, with impacts starting only a week before the major
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impacts. The western debris trail, on the other hand, will impact Jupiter
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over a period of months following the main impacts, with the latter portion
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of the trail actually impacting on the front side of Jupiter as viewed from
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Earth.
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The injection of dust from the wings and tail into the Jovian system
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may have several consequences. First, the dust will absorb many of the
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energetic particles that currently produce radio emissions in the Jovian
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magnetosphere. The expected decline and recovery of the radio emission may
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occur over as long as several years, and yield information on the nature and
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origin of the energetic particles. Second, the dust may actually form a
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second faint ring around the planet.
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Q1.5: Can I see the effects in my telescope?
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One might be able to detect atmospheric changes on Jupiter using
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photography or CCD imaging. It is important, however, to observe Jupiter
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for several months in advance in order to know which features are due to
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impacts and which are naturally occurring. It appears more and more likely
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that most effects will be quite subtle. Without a large ( > 15" ?) telescope
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and good detector, little is likely to be seen.
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It is possible that the impacts may create a new, temporary storm at the
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latitude of the impacts. Modeling by Harrington et al. suggests this is
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possible [30]. The fragments of comet Shoemaker-Levy 9 will strike just
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south of the South South Temperate Belt of Jupiter. If the nuclei penetrate
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deep enough, water vapor may shoot high into the atmosphere where it could
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turn into a bluish shroud over a portion of the South South Temperate Zone
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[31].
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Impacts of the largest fragments may create one or two features. A spot
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might develop that could be a white or dark blue nodule and would likely have
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a maximum diameter of 2,000 km to 2,500 km which in a telescope would be 1
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to 1.5 arcseconds across. This feature would be very short-lived with the
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impact site probably returning to normal after just a few rotations of
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Jupiter. A plume might also develop that would look dark against the South
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Temperate Zone's white clouds or could appear as a bright jet projected from
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Jupiter limb [31]. The table below shows the approximate sizes of features
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that already exist on Jupiter for comparison.
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+====================================================================+
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| FEATURE SIZE ESTIMATES |
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+====================================================================+
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| Great Red Spot 29000 by 12000 km [32] |
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| White Spots FA,BC,DE 7500 by 3000 km |
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| Shadows of Io, Europa, and Ganymede 4300, 4200, 7100 km |
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+====================================================================+
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Below is a list of files available at tamsun.tamu.edu in the /pub/comet
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directory that may be helpful in identifying features on Jupiter:
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tracker2.zip MSDOS program that displays the location of impact sites
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jupe.description Description of a PC program showing features of Jupiter
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jun1994.transit Transit Times for Red Spot and White Spots for May 1994
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jun1994.moons Jovian Moon events for May 1994 (Shadows, Eclipses, etc.)
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Also, there are little anticyclonic ovals at latitudes of about -41
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degrees which are typical of the South South Temperate domain. There are
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usually 6 or 7 around the planet and they move with the South South
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Temperate current, i.e. faster than BC and DE. See Sky & Telescope
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for a photo of these ovals by Don Parker [38].
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* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
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SPECIFICS
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Q2.1: What are the impact times and impact locations?
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This information was provided P.W. Chodas and D.K. Yeomans:
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============================================================================
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Predicted Impact Parameters for Fragments of P/Shoemaker-Levy 9
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P.W. Chodas and D.K. Yeomans (JPL/Caltech)
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Predictions as of 1994 June 3
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Date of last astrometric data in these solutions: 1994 June 1
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Immediately to the right of the predicted impact times, we give the 1-sigma
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uncertainties in those times for all fragments except Q2. We have made an
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effort to make these uncertainties realistic: they are not formal uncertainty
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values. NOTE: To obtain a 95% confidence level, one should use a +/- 2 sigma
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window around the predicted impact time. The uncertainties for fragment Q2
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have not been quantified, but are probably comparable to those for P2.
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The dynamical model used for the predictions includes perturbations due to
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the Sun, planets, Galilean satellites and the oblateness of Jupiter. The
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planetary ephemeris used was DE245.
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----------------------------------------------------------------
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Fragment Impact 1-sig Jovicentric Meridian Angle
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Date/Time Unc. Lat. Long. Angle E-J-F Orbit
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July (UT) (min) (deg) (deg) (deg) (deg) Ref.
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---------------h--m---------------------------------------------
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A = 21 16 19:55 26 -43.23 176 63.56 99.35 A10
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B = 20 17 03:07 23 -43.45 77 63.67 99.22 B11
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C = 19 17 06:59 24 -43.33 217 64.53 98.64 C8
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D = 18 17 11:18 28 -43.34 14 63.49 99.36 D9
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E = 17 17 15:30 17 -43.70 164 66.13 97.41 E25
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F = 16 18 00:40 23 -43.79 139 64.17 98.77 F16
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G = 15 18 07:52 16 -43.80 37 66.99 96.77 G25
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H = 14 18 19:47 16 -43.86 109 67.32 96.52 H23
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K = 12 19 10:39 16 -43.96 287 68.15 95.90 K24
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L = 11 19 22:40 16 -44.07 2 68.95 95.31 L25
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N = 9 20 10:21 26 -44.59 67 67.13 96.49 N12
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P2= 8b 20 15:27 25 -44.82 253 66.46 96.91 P11
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Q2= 7b 20 19:49 -44.48 48 69.27 95.00
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Q1= 7a 20 20:16 15 -44.20 64 69.69 94.75 Q27
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R = 6 21 05:59 19 -44.27 57 70.24 94.34 R22
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S = 5 21 15:46 17 -44.26 51 70.76 93.97 S32
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T = 4 21 18:16 44 -45.28 145 67.43 96.14 T7
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U = 3 22 00:25 85 -45.19 3 71.74 93.15 U6
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V = 2 22 04:06 31 -44.52 141 68.16 95.77 V8
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W = 1 22 08:34 19 -44.29 299 71.32 93.57 W25
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Notes:
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1. Fragments J=13 and M=10 are omitted because they have faded from view.
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Fragments P=8 and Q=7 each consist of multiple components. The March'94
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HST image shows that P1=8a has almost completely faded away (so it too is
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omitted from the Table), and that P2=8b has split. We do not as yet
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have sufficient data to obtain independent predictions for the two
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components of P2=8b.
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2. The impact date/time is the time the impact would be seen at the Earth
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(if the limb of Jupiter were not in the way); the date is the day in
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July 1994; the time is given as hours and minutes of Universal Time.
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3. The impact latitude is Jovicentric (latitude measured at the center of
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Jupiter); the Jovigraphic latitudes are about 3.84 deg more negative.
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4. The impact longitude is in System II, measured westwards on the planet.
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5. The meridian angle is the Jovicentric longitude of impact measured from
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the midnight meridian towards the morning terminator. This relative
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longitude is known much more accurately than the absolute longitude.
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6. Angle E-J-F is the Earth-Jupiter-Fragment angle at impact; values greater
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than 90 deg indicate a farside impact. All impacts will be just on the
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farside as viewed from Earth; later impacts are closer to the limb.
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7. The angle of incidence of the impacts is between 41 and 42 degrees
|
|
for all the fragments.
|
|
|
|
============================================================================
|
|
|
|
See "impacts.*" at SEDS.LPL.Arizona.EDU in the /pub/astro/SL9/info
|
|
directory for updates and more details about these predictions. The
|
|
following are the 1-sigma (uncertainty) predictions for the fragment impact
|
|
times:
|
|
on March 1 - 30 min
|
|
on May 1 - 24 min
|
|
on June 1 - 16 min
|
|
on July 1 - 10 min
|
|
on July 15 - 6 min
|
|
at impact - 18 hr - 3 min
|
|
|
|
The time between impacts is thought to be known with more certainty than the
|
|
actual impact times. This means that if somehow the impact time of the first
|
|
fragment can be measured experimentally, then impact times of the fragments
|
|
that follow can be predicted with more accuracy.
|
|
|
|
|
|
Q2.2: Can the collision be observed with radio telescopes?
|
|
|
|
The cutoff of radio emissions due to the entry of cometary dust into the
|
|
Jovian magnetosphere during the weeks around impact may be clear enough to be
|
|
detected by small radio telescopes. Furthermore, impacts may be directly
|
|
detectable in radio frequencies. Some suggest to listen in on 15-30 MHz
|
|
during the comet impact. So it appears that one could use the same antenna
|
|
for both the Jupiter/Io phenomenon and the Jupiter/comet impact. There is
|
|
an article in Sky & Telescope magazine which explains how to build a simple
|
|
antenna for observing the Jupiter/Io interaction [4,24,25].
|
|
For those interested in radio observations during the SL9 impact,
|
|
Leonard Garcia of the University of Florida has made some information
|
|
available. The following files are available via anonymous ftp on the
|
|
University of Florida, Department of Astronomy site astro.ufl.edu in the
|
|
/pub/jupiter directory:
|
|
|
|
README.DOC Explanation of predicted Jupiter radio storms tables
|
|
jupradio.txt Jovian Decametric Emission and the SL9/Jupiter Collision
|
|
jupradio.ps Postscript version of jupradio.txt
|
|
hist.ps Histogram of occurrence probabilities of Jupiter radio
|
|
emission at different frequencies.
|
|
may94.txt Tables of predicted Jupiter radio storms for May 1994
|
|
june94.txt Tables of predicted Jupiter radio storms for June 1994
|
|
july94.txt Tables of predicted Jupiter radio storms for July 1994
|
|
|
|
The antenna required to observe Jupiter may be as simple as a dipole
|
|
antenna constructed with two pieces of wire 11 feet 8.4 inches in length,
|
|
connected to a 50 ohm coax cable. This antenna should be laid out on a
|
|
East-West line and raised above the ground by at least seven feet. A
|
|
Directional Discontinuity Ring Radiator (DDRR) antenna is also easy to
|
|
construct and can be made from 1/2 inch copper tubing 125.5 inches in
|
|
length (21Mhz). The copper tube should be bent into a loop and placed 5
|
|
inches above a metallic screen. A good preamp is required for
|
|
less sensitive shortwave receivers [39].
|
|
|
|
|
|
Q2.3: Will light from the explosions be reflected by any moons?
|
|
|
|
One may be able to witness the collisions indirectly by monitoring the
|
|
brightness of the Galilean moons that may be behind Jupiter as seen from
|
|
Earth. One could monitor the moons using a photometer, a CCD camera, or a
|
|
video camera. However, current calculations suggest that the brightenings
|
|
may be as little as 0.05% of the sunlit brightness of the moon [18]. If a
|
|
moon can be caught in eclipse but visible from the earth during an impact,
|
|
prospects will improve significantly. According to current predictions,
|
|
the only impact certain to occur during a satellite eclipse is K=12 with
|
|
Europa eclipsed. However, H=14 and W=1 impact only about 2 sigma after Io
|
|
emerges from eclipse at longitude 20 deg, and B=20, E=17 and F=16 impact
|
|
0.5-2 sigma after Amalthea emerges from eclipse at longitude 34 deg.
|
|
The following files contain information concerning the reflection of
|
|
light by Jupiter's moons and are available at SEDS.LPL.Arizona.EDU :
|
|
|
|
galsat52.zip MSDOS Program that Displays relative positions of
|
|
Jupiter's Moons during times of impact
|
|
impact_24apr.ps PostScript Plot of impact times at satellite availability
|
|
jsat8.* Jovian satellite locations
|
|
|
|
The following information was provided by John Spencer, 11 Apr 1994:
|
|
===========================================================================
|
|
|
|
COMET IMPACT SATELLITE REFLECTIONS
|
|
|
|
Here's an updated table of satellite reflector availability, based on
|
|
the latest (1994/02/23) Chodas and Yeomans ephemerides. Times haven't
|
|
changed much but uncertainties have gone down. No impact times are yet
|
|
available for P1=8a and Q2=7b.
|
|
|
|
In the table, a "+" next to the orbital longitude means that the
|
|
impact will be visible from the satellite. Longitudes greater than 90
|
|
degrees will be less useful as the phase angle of the reflected light
|
|
(to first order, equal to the longitude) will be high and its
|
|
brightness will be greatly reduced. An "e" means the satellite will
|
|
be visible in eclipse, allowing higher sensitivity observations, and
|
|
an "o" means it will be occulted by Jupiter. I've included Callisto
|
|
(J4) for completeness but it's likely to be too far out to be useful-
|
|
the same may be true for Ganymede (J3).
|
|
|
|
---------------------------------------------------------
|
|
UT Satellite Orbital Longitudes
|
|
date of Bright (degrees past superior conj.)
|
|
impact -ness ---------------------------------
|
|
Nucleus (July) Index J5 J1 J2 J3 J4
|
|
---------------------------------------------------------
|
|
A=21 16.81 1 193 340 103+ 75+ 35+
|
|
B=20 17.11 1 50+ 41+ 133+ 90+ 42+
|
|
C=19 17.27 1 165 74+ 149+ 98+ 45+
|
|
D=18 17.48 1 317 116+ 171 109+ 50+
|
|
E=17 17.61 2 51+ 143+ 184 116+ 52+
|
|
F=16 18.02 2 347o 226 225 136+ 61+
|
|
G=15 18.30 3 190 283 254 150+ 67+
|
|
H=14 18.78 3 177 21+ 302 174 78+
|
|
K=12 19.42 3 279 151+ 7e 207 91+
|
|
L=11 19.89 3 259 246 55+ 230 101+
|
|
N=9 20.41 1 274 352o 107+ 256 113+
|
|
P2=8b 20.61 2 59+ 33+ 128+ 266 117+
|
|
P1=8a 1
|
|
Q2=7b 2
|
|
Q1=7a 20.80 3 196 72+ 147+ 276 121+
|
|
R=6 21.28 2 183 169+ 196 300 131+
|
|
S=5 21.61 3 61+ 236 229 317 138+
|
|
T=4 21.75 1 162 265 243 324 141+
|
|
U=3 21.88 1 256 291 256 330 144+
|
|
V=2 22.18 2 113+ 352o 287 345 151+
|
|
W=1 22.32 2 214 21+ 301 352+ 154+
|
|
Uncertainties (1-sigma):
|
|
0.03 1 22 6 3 1.5 1
|
|
---------------------------------------------------------
|
|
|
|
The "brightness index" subjectively rates comet fragment
|
|
brightnesses, 3 being brightest. Brightnesses are eyeballed from
|
|
the press-released HST image where possible and are different from
|
|
those in previous versions of the table.
|
|
|
|
There's a good chance that reflections from the impact of the bright
|
|
fragment K=12 will be visible off Europa in eclipse, very close to
|
|
Jupiter: this impact can be seen in a dark sky from Australia, New
|
|
Zealand, and Hawaii.
|
|
|
|
Given the uncertainties, there's nearly a 50% chance that the impact
|
|
of either H=14 (a bright fragment) or W=1 will be seen reflected off Io
|
|
in eclipse. The H=14 impact will be visible in darkness from East and
|
|
South Africa, and the middle East, the W=1 impact from New Zealand and
|
|
Hawaii.
|
|
|
|
The table below gives the orbital longitudes (in degrees) of
|
|
satellites when in Jupiter eclipse and occultation (used to annotate
|
|
the above table). Values should be good to about one degree.
|
|
|
|
-------------------------------------
|
|
Satellite Occulted Eclipsed
|
|
-------------------------------------
|
|
J5: Amalthea 337 - 023 023 - 034
|
|
J1: Io 351 - 009 009 - 020
|
|
J2: Europa 355 - 005 005 - 016
|
|
J3: Ganymede 358 - 002 009 - 013
|
|
J4: Callisto No occultations or eclipses
|
|
------------------------------------
|
|
|
|
See "satellites.*" at SEDS.LPL.Arizona.EDU in the /pub/astro/SL9/info
|
|
directory for updates.
|
|
|
|
===========================================================================
|
|
|
|
Also, monitoring the eclipses of the Galilean satellites after the
|
|
impacts may yield valuable scientific data with the moons serving as
|
|
sensitive probes of any cometary dust in Jupiter's atmosphere. The geometry
|
|
of the eclipses is such that the satellites pass through the shadow at
|
|
roughly the same latitude as the predicted comet impacts. There is an
|
|
article in the first issue of CCD Astronomy involving these observations.
|
|
The article says that if the dust were to obscure sunlight approximately
|
|
120 kilometers above Jupiter's cloud tops, Io could be more that 3 percent
|
|
(0.03 magnitudes) fainter than normal at mideclipse [40].
|
|
|
|
|
|
Q2.4: What are the orbital parameters of the comet?
|
|
|
|
Comet Shoemaker-Levy 9 is actually orbiting Jupiter, which is most
|
|
unusual: comets usually just orbit the Sun. Only two comets have ever been
|
|
known to orbit a planet (Jupiter in both cases), and this was inferred in
|
|
both cases by extrapolating their motion backwards to a time before they
|
|
were discovered. S-L 9 is the first comet observed while orbiting a planet.
|
|
Shoemaker-Levy 9's previous closest approach to Jupiter (when it broke up)
|
|
was on July 7, 1992; the distance from the center of Jupiter was about
|
|
96,000 km, or about 1.3 Jupiter radii. The comet is thought to have reached
|
|
apojove (farthest from Jupiter) on July 14, 1993 at a distance of about 0.33
|
|
Astronomical Units from Jupiter's center. The orbit is very elliptical,
|
|
with an eccentricity of over 0.998. Computations by Paul Chodas, Zdenek
|
|
Sekanina, and Don Yeomans, suggest that the comet has been orbiting Jupiter
|
|
for 20 years or more, but these backward extrapolations of motion are highly
|
|
uncertain. See "elements.*" and "ephemeris.*" at SEDS.LPL.Arizona.EDU in
|
|
/pub/astro/SL9/info for more information.
|
|
In the abstract "The Orbit of Comet Shoemaker-Levy 9 about Jupiter"
|
|
by D.K. Yeomans and P.W. Chodas (1994, BAAS, 26, 1022), the elements
|
|
for the brightest fragment Q are listed. These elements are Jovicentric
|
|
and for Epoch 1994Jul15 (J2000 ecliptic):
|
|
|
|
1994 Periapses Jul 20.7846
|
|
Eccentricity 0.9987338
|
|
Periapses dist. 34776.7 km
|
|
Arg. of periapses 43.47999
|
|
Long. of asc. node 290.87450
|
|
inclination 94.23333
|
|
|
|
|
|
Q2.5: Why did the comet break apart?
|
|
|
|
The comet broke apart due to tidal forces on its closest approach to
|
|
Jupiter (perijove) on July 7, 1992 when it passed within the theoretical
|
|
Roche limit of Jupiter. Shoemaker-Levy 9 is not the first comet observed
|
|
to break apart. Comet West shattered in 1976 near the Sun [3]. Astronomers
|
|
believe that in 1886 Comet Brooks 2 was ripped apart by tidal forces near
|
|
Jupiter [2]. Several other comets have also been observed to have split
|
|
[41].
|
|
Furthermore, images of Callisto and Ganymede show crater chains which
|
|
may have resulted from the impact of a shattered comet similar to Shoemaker-
|
|
Levy 9 [3,17]. The satellite with the best example of aligned craters is
|
|
Callisto with 13 crater chains. There are three crater chains on Ganymede.
|
|
These were first thought to be from basin ejecta; in other words secondary
|
|
craters. See Q1.3 and [27] for images of crater chains.
|
|
There are also a few examples of crater chains on our Moon. Jay Melosh
|
|
and Ewen Whitaker have identified 2 possible crater chains on the moon which
|
|
would be generated by near-Earth tidal breakup. One is called the "Davy
|
|
chain" and it is very tiny but shows up as a small chain of craters aligned
|
|
back toward Ptolemaeus. In near opposition images, it appears as a high
|
|
albedo line; in high phase angle images, you can see the craters themselves.
|
|
The second is between Almanon and Tacitus and is larger (comparable to the
|
|
Ganymede and Callisto chains in size and length).
|
|
|
|
|
|
Q2.6: What are the sizes of the fragments?
|
|
|
|
Using measurements of the length of the train of fragments and a model
|
|
for the tidal disruption, J.V. Scotti and H.J. Melosh have estimated that the
|
|
parent nucleus of the comet (before breakup) was only about 2 km across [13].
|
|
This would imply that the individual fragments are no larger than about 500
|
|
meters across. Images of the comet taken with the Hubble Space Telescope in
|
|
July 1993 indicate that the fragments are 3-4 km in diameter (3-4 km is an
|
|
upper limit based on their brightness). A more elaborate tidal disruption
|
|
model by Sekanina, Chodas and Yeomans [20] predicts that the original comet
|
|
nucleus was at least 10 km in diameter. This means the largest fragments
|
|
could be 3-4 km across, a size consistent with estimates derived from the
|
|
Hubble Space Telescope's July 1993 observations.
|
|
The new images, taken with the Hubble telescope's new Wide Field and
|
|
Planetary Camera-II instrument on January 24-27, 1994, have given us an even
|
|
clearer view of this fascinating object, which should allow a refinement of
|
|
the size estimates. In addition, the new images show strong evidence for
|
|
continuing fragmentation of some of the remaining nuclei, which will be
|
|
monitored by the Hubble telescope over the next month.
|
|
|
|
|
|
Q2.7: How long is the fragment train?
|
|
|
|
The angular length of the train was about 51 arcseconds in March 1993
|
|
[2]. The length of the train then was about one half the Earth-Moon
|
|
distance. In the day just prior to impact, the fragment train will stretch
|
|
across 20 arcminutes of the sky, more that half the Moon's angular diameter.
|
|
This translates to a physical length of about 5 million kilometers. The
|
|
train expands in length due to differential orbital motion between the first
|
|
and last fragments. Below is a table with data on train length based on
|
|
Sekanina, Chodas, and Yeomans's tidal disruption model:
|
|
|
|
+=============================================+
|
|
| Date Angular Length Physical Length |
|
|
| (arcsec) (km) |
|
|
+=============================================+
|
|
| 93 Mar 25 49 158,000 |
|
|
| Jul 1 67 265,000 |
|
|
| 94 Jan 1 131 584,000 |
|
|
| Feb 1 161 669,000 |
|
|
| Mar 1 200 762,000 |
|
|
| Apr 1 255 893,000 |
|
|
| May 1 319 1,070,000 |
|
|
| Jun 1 400 1,366,000 |
|
|
| Jul 1 563 2,059,000 |
|
|
| Jul 15 944 3,593,000 |
|
|
| Impact A 1286 4,907,000 |
|
|
+=============================================+
|
|
|
|
|
|
Q2.8: Will Hubble, Galileo, etc. be able to observe the collisions?
|
|
|
|
The Hubble Space Telescope, like earthlings, will not be able to see the
|
|
collisions but will be able to monitor atmospheric changes on Jupiter. The
|
|
new impact points are more favorable for viewing from spacecraft: it can now
|
|
be stated with certainty that the impacts will all be visible to Galileo,
|
|
and now at least some impacts will be visible to Ulysses. Although Ulysses
|
|
does not have a camera, it will monitor the impacts at radio wavelengths.
|
|
Galileo will get a direct view of the impacts rather than the grazing
|
|
limb view previously expected. The Ida image data playback is scheduled to
|
|
end at the end of June, so there should be no tape recorder conflicts with
|
|
observing the comet fragments colliding with Jupiter. The problem is how to
|
|
get the most data played back when Galileo will only be transmitting at 10
|
|
bps. One solution is to have both Ulysses and Galileo record the event and
|
|
and store the data on their respective tape recorders. Ulysses observations
|
|
of radio emissions data will be played back first and will at least give
|
|
the time of each comet fragment impact. Using this information, data can
|
|
be selectively played back from Galileo's tape recorder. From Galileo's
|
|
perspective, Jupiter will be 60 pixels wide and the impacts will only show
|
|
up at about 1 pixel, but valuable science data can still collected in the
|
|
visible and IR spectrum along with radio wave emissions from the impacts.
|
|
The impact points are also viewable by both Voyager spacecraft,
|
|
especially Voyager 2. Jupiter will appear as 2.5 pixels from Voyager 2's
|
|
viewpoint and 2.0 pixels for Voyager 1. However, it is doubtful that the
|
|
Voyagers will image the impacts because the onboard software that controls
|
|
the cameras has been deleted, and there is insufficient time to restore and
|
|
test the camera software. The only Voyager instruments likely to observe
|
|
the impacts are the ultraviolet spectrometer and planetary radio astronomy
|
|
instrument. Voyager 1 will be 52 AU from Jupiter and will have a near-limb
|
|
observation viewpoint. Voyager 2 will be in a better position to view the
|
|
collision from a perspective of looking directly down on the impacts, and
|
|
it is also closer at 41 AU.
|
|
|
|
|
|
Q2.9: To whom can I report my observations?
|
|
|
|
Observation forms by Steve Lucas are available via ftp at
|
|
oak.oakland.edu in the /pub/msdos/astrnomy directory. These forms also
|
|
contain addresses of "Jupiter Watch Program" section leaders. jupcom02.zip
|
|
contains Microsoft Write files. The Association of Lunar and Planetary
|
|
Observers (ALPO) will also distribute a handbook to interested observers.
|
|
The handbook "The Great Crash of 1994" is available for $10 by
|
|
|
|
ALPO Jupiter Recorder
|
|
Phillip W. Budine
|
|
R.D. 3, Box 145C
|
|
Walton, NY 13856 U.S.A.
|
|
|
|
The cost includes printing, postage and handling.
|
|
John Rogers, the Jupiter Section Director for the British Astronomical
|
|
Association, will be collecting data from regular amateur Jupiter observers
|
|
in Britain and worldwide. He can be reached via email (jr@mole.bio.cam.ac.U)
|
|
or fax (UK [223] 333840). For other addresses see page 44 of the January
|
|
1994 issue of Sky & Telescope magazine [14].
|
|
|
|
|
|
Q2.10: Where can I find more information?
|
|
|
|
The SL9 educator's book put out by JPL is in the /pub/astro/SL9/EDUCATOR
|
|
directory of SEDS.LPL.Arizona.edu. There are two technical papers [18,19]
|
|
on the atmospheric consequences of the explosions available at
|
|
oddjob.uchicago.edu in the /pub/jupiter directory. There are some
|
|
PostScript images and text files involving the results of fireball simulations
|
|
by Sandia National Laboratories at tamsun.tamu.edu (128.194.15.32) in the
|
|
/pub/comet/sandia directory.
|
|
SEDS (Students for the Exploration and Development of Space) has set up
|
|
an anonymous account which allows you to use "lynx" - a VT100 WWW browser.
|
|
To access this service, telnet to SEDS.LPL.Arizona.EDU and login as "www"
|
|
(no password required). This will place you at the SEDS home page, from
|
|
which you can select Shoemaker-Levy 9. A similar "gopher" interface is
|
|
available at the same site. Just login as "gopher".
|
|
Below is a list of FTP and WWW sites with SL9 information:
|
|
|
|
===============================================================================
|
|
FTP SITE NAME IP ADDRESS DIRECTORY CONTENTS
|
|
===============================================================================
|
|
SEDS.LPL.Arizona.EDU (128.196.64.66) /pub/astro/SL9 Images & Info
|
|
jwd.ping.de /pub/people/hh/astro/comet SEDS Mirror
|
|
oddjob.uchicago.edu /pub/jupiter Articles
|
|
jplinfo.jpl.nasa.gov (137.78.104.2) /news and /images Images
|
|
ftp.cicb.fr (129.20.128.34) /pub/Images/ASTRO/hst Images
|
|
tamsun.tamu.edu (128.194.15.32) /pub/comet Images & Info
|
|
|
|
===============================================================================
|
|
WORLD WIDE WEB SITES CONTENTS
|
|
===============================================================================
|
|
http://info.cv.nrao.edu/staff/pmurphy/jove-comet-wham-2.html Info & Images
|
|
http://seds.lpl.arizona.edu/sl9/sl9.html Images & Info
|
|
http://pscinfo.psc.edu/research/user_research/user_research.html Animations
|
|
|
|
If you have only mail access then try emailing the following message
|
|
(no subject) to bitftp@pucc.Princeton.edu:
|
|
|
|
ftp SEDS.LPL.Arizona.EDU
|
|
user anonymous guest
|
|
cd pub
|
|
cd astro
|
|
cd SL9
|
|
dir
|
|
cd info
|
|
get factsheet.txt
|
|
|
|
The file "factsheet.txt" should then be mailed to your account. Other files
|
|
can be retrieved in a similar manner. For more info email the following
|
|
message to bitftp@pucc.Princeton.edu:
|
|
|
|
help
|
|
howtoftp
|
|
|
|
* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
|
|
|
|
REFERENCES
|
|
|
|
[1] "Update on the Great Comet Crash", Astronomy, December 1993, page 18.
|
|
[2] Levy, David H., "Pearls on a String", Sky & Telescope, July 1993,
|
|
page 38-39.
|
|
[3] Melosh, H. H. and P. Schenk, "Split comets and the origin of crater
|
|
chains on Ganymede and Callisto" Nature 365, 731-733 (1993).
|
|
[4] "Jupiter on Your Shortwave", Sky & Telescope, December 1989, page 628.
|
|
[5] "Comet on a String", Sky & Telescope, June 1993, page 8-9.
|
|
[6] "Comet Shoemaker-Levy (1993e)", Astronomy, July 1993, page 18.
|
|
[7] "A Chain of Nuclei", Astronomy, August 1993, page 18.
|
|
[8] "When Worlds Collide : Comet will Hit Jupiter", Astronomy,
|
|
September 1993, page 18.
|
|
[9] Burnham, Robert "Jove's Hammer", Astronomy, October 1993, page 38-39.
|
|
[10] IAU Circulars : 5800, 5801, 5807, 5892, and 5893
|
|
[11] Observers Handbook 1994 of the R.A.S.C., Brian Marsden.
|
|
[12] Sekanina, Zdenek, "Disintegration Phenomena Expected During Collision
|
|
of Comet Shoemaker-Levy 9 with Jupiter" Science 262, 382-387 (1993).
|
|
[13] Scotti, J. V. and H. J. Melosh, "Estimate of the size of comet
|
|
Shoemaker-Levy 9 from a tidal breakup model" Nature 365, 733-735 (1993).
|
|
[14] Beatty, Kelly and Levy, David H., "Awaiting the Crash" Sky & Telescope,
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January 1994, page 40-44.
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[15] Jewitt et al., Bull. Am. Astron. Soc. 25, 1042, (1993).
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[16] "AstroNews", Astronomy, January 1994, page 19.
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[17] "AstroNews", Astronomy, February 1994, page 16.
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[18] Zahnle, Kevin and Mac Low, Mordecai-Mark, "The Collisions of Jupiter and
|
|
Comet Shoemaker Levy 9", submitted to Icarus October 29, 1993.
|
|
[19] Mac Low, Mordecai-Mark and Zahnle, Kevin "Explosion of Comet
|
|
Shoemaker-Levy 9 on Entry into the Jovian Atmosphere",
|
|
submitted to Science on 10 February 1994.
|
|
[20] Sekanina, Z., Chodas, P.W., and Yeomans, D.K, "Tidal Disruption and the
|
|
Appearance of Periodic Comet Shoemaker-Levy 9", Astronomy &
|
|
Astrophysics, in press.
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|
[21] "On a collision Course with Jupiter", Mercury, Nov-Dec 1993, page 15-16.
|
|
[22] "Timing the Crash", Sky & Telescope, February 1994, page 11.
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|
[23] "Capturing Jupiter on Video" Sky & Telescope, September 1993, page 102.
|
|
[24] North, Gerald, "Advanced Amateur Astronomy", page 296-298, (1991).
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|
[25] "Backyard Radio Astronomy", Astronomy, March 1983, page 75-77.
|
|
[26] Harrington, J., R. P. LeBeau, K. A. Backes, and T. E. Dowling,
|
|
"Dynamic response of Jupiter's atmosphere to the impact of comet
|
|
Shoemaker-Levy 9" Nature 368: 525-527 (1994).
|
|
[27] David Morrison, "Satellites of Jupiter", page 392, (1982).
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|
[28] Weaver, H. A., P. D. Feldman, M. F. A'Hearn, C. Arpigny, R. A. Brown,
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|
E. F. Helin, D. H. Levy, B. G. Marsden, K. J. Meech, S. M. Larson,
|
|
K. S. Knoll, J. V. Scotti, Z. Sekanina, C. S. Shoemaker, E. M. Shoemaker,
|
|
T. E. Smith, A. D. Storrs, D. K. Yeomans, and B. Zellner,
|
|
"Hubble Space Telescope Observations of Comet P/Shoemaker-Levy 9 (1993e)."
|
|
Science 263, page 787-791, (1994).
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|
[29] Duffy, T.S., W.L. Vos, C.S. Zha, H.K. Mao, and R.J. Hemley. "Sound
|
|
Velocities in Dense Hydrogen and the Interior of Jupiter" Science 263,
|
|
page 1590-1593, (1994).
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|
[30] Harrington, J., R. P. LeBeau, K. A. Backes, & T. E. Dowling, "Dynamic
|
|
response of Jupiter's atmosphere to the impact of comet P/Shoemaker-
|
|
Levy 9", Nature 368, page 525-527, April 7, 1994.
|
|
[31] Olivares, Jose, "Jupiter's Magnificent Show", Astronomy, April 1994,
|
|
page 74-79.
|
|
[32] Schmude, Richard W., "Observations of Jupiter During the 1989-90
|
|
Apparition", The Strolling Astronomer: J.A.L.P.O., Vol. 35, No. 3.,
|
|
September 1991.
|
|
[33] "Comet heads for collision with Jupiter",Aerospace America,April 1994,
|
|
page 24-29.
|
|
[34] "Comet Shoemaker-Levy 9 and Galilean Eclipses", CCD Astronomy, Spring
|
|
1994, page 18-19.
|
|
[35] Reston, James Jr., "Collision Course", TIME, May 23, 1994, page 54-61.
|
|
[36] "Boom or Bust", Physics Today, June 1994, page 19-21.
|
|
[37] Beatty, Kelly and Levy, David H., "Awaiting the Crash - Part II", Sky
|
|
& Telescope, July 1994, page 18-23.
|
|
[38] Alan M. MacRobert, "Observing Jupiter at Impact Time", Sky & Telescope,
|
|
July 1994, page 31-35.
|
|
[39] Van Horn, Larry, "Countdown to the Crash", Monitoring Times, June 1994,
|
|
page 10-13.
|
|
[40] Mallama, Anthony, "Comet Shoemaker-Levy 9 and Galilean Satellite
|
|
Eclipses", CCD Astronomy, Spring 1994, pages 18-19.
|
|
[41] B. M. Middlehurst and G. P. Kuiper, "The Moon, Meteorites
|
|
and Comets", Univ. Chicago Press, 1963.
|
|
[42] Boslough, Mark B., et al, "Determination of Mass and Penetration Depth
|
|
of Shoemaker-Levy 9 fragments from time-resolved impact flashed signatures"
|
|
submitted to Geophysical Research Letters, June 1994.
|
|
[43] Crawford, David A., et al, "The impact of Comet Shoemaker-Levy 9 on
|
|
Jupiter", submitted to Shock Waves, April 1994.
|
|
[44] Bruning, David, "The Comet Crash", Astronomy, June 1994, pages 41-45.
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|
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ACKNOWLEDGMENTS
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Thanks to Ross Smith for starting a FAQ and to all those who have
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contributed : Robb Linenschmidt, Mordecai-Mark Mac Low, Phil Stooke,
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|
Rik Hill, Elizabeth Roettger, Ben Zellner, Kevin Zahnle, Ron Baalke,
|
|
David H. Levy, Eugene and Carolyn Shoemaker, Jim Scotti, Richard A.
|
|
Schumacher, Louis A. D'Amario, John McDonald, Michael Moroney, Byron
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|
Han, Wayne Hayes, David Tholen, Patrick P. Murphy, Greg F Walz Chojnacki,
|
|
Jeffrey A. Foust, Paul Martz, Kathy Rages, Paul Chodas, Zdenek Sekanina,
|
|
Don Yeomans, Richard Schmude, Lenny Abbey, Chris Lewicki, the Students
|
|
for the Exploration and Development of Space (SEDS), David A. Seal,
|
|
Leonard Garcia, Raymond Doyle Benge, Mark Boslough, Dave Mehringer,
|
|
John Spencer, Erik Max Francis, and John Rogers.
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* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
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SL9 LIVE
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The following messages discuss how one could get live updates:
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/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\
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Hello, I'm Jim Moskowitz of the Franklin Institute Science Museum. I was
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(tangentially) involved in the 'Neptune All Night' live broadcast we did
|
|
over PBS during the '89 Voyager flyby, and I've just learned that we're
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|
going to be doing a PBS broadcast for SL9 as well.
|
|
On Wednesday, July 20th, from 10:30 to 11:30 PM EST we'll be providing
|
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PBS stations with a show talking about the impacts and their effects,
|
|
featuring images from Hubble, discussion with Levy and the Shoemakers,
|
|
a piece by Arthur C. Clarke, and probably much more.
|
|
My understanding is that it will be up to the local PBS stations to decide
|
|
whether to show this program (as opposed to, maybe, an 'Eastenders' rerun).
|
|
You may want to call your area station and express interest in having the
|
|
program shown in your area...
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-Jim (jimmosk@fi.edu)
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/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\
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The Fernbank Science Center in Atlanta, Georgia, USA is planning to have
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|
a video link from their 36-inch telescope down to their planetarium,
|
|
so people can view the results of the impact of comet Shoemaker-Levy 9
|
|
with Jupiter. Currently, they are working on a press release and hope
|
|
to have their plans finalized in June.
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For more information call or write:
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Fernbank Science Center
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156 Heaton Park Drive, NE
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Atlanta, Georgia 30307
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USA 404-378-4311
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/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\
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There may be continuous discussion/updates on the IRC (Internet Relay
|
|
chat) channel #Astronomy during the impacts.
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/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\
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Article: 4 of jpl.shoemaker-levy
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Subject: Galileo's Observing Plans
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|
Preview of Galileo's Tentative SL-9 Observing Plans
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|
Clark R. Chapman
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(cchapman@nasamail.nasa.gov)
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|
6 April 1994
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|
Nearly all observations of the SL-9 impacts will be made from the
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|
Earth, or from Earth-orbiting observatories. Several spacecraft will also
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|
be observing Jupiter in mid-July. However, the Galileo spacecraft, headed
|
|
for Jupiter orbit in late 1995, has the best seat in the house. It will be
|
|
the only observatory capable of actually "seeing" (i.e. resolving) the
|
|
impacts directly: the impact sites will be on the side of Jupiter facing the
|
|
spacecraft, and Galileo's CCD camera can resolve phenomena on Jupiter as
|
|
well as can be done from most ground-based observatories (Jupiter will be
|
|
about 60 pixels across). Other Galileo instruments will be observing, as
|
|
well.
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|
The sequences are currently being designed and there is little room
|
|
for further modification. Moreover, the work is being done with a
|
|
shoestring budget on a "best effort" basis. The information below is
|
|
tentative and may be inaccurate in some respects. It is being provided, at
|
|
the request of the managers of the bulletin board, in the interest of
|
|
developing needed coordination.
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|
|
The premier data will be taken with Galileo's camera. About 6 of the
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|
19 impacts (tentatively D, E, K, N, V, and W) will be imaged in one of two
|
|
basic ways. For half of the opportunities, the camera will snap pictures in
|
|
a time-lapse mode using a new on-chip mosaicking capability. Images will
|
|
be recorded every 2 1/3 second (tentatively for fragment N) through the
|
|
period that includes the bolide flash and any subsequent fireball and
|
|
lasting until the impact site rotates past Jupiter's morning terminator
|
|
(typically 6 to 10 minutes later). Pictures will be taken every 8 2/3
|
|
seconds for two other events (probably V and D), which would permit
|
|
successive images to be taken through a repeated cycle of 4 color filters
|
|
and will reduce the 33% dead-time that characterizes the 2 1/3 second
|
|
mode; this 8 2/3 second mode is more conservative of resources but would
|
|
permit a brief bolide to slip through undetected, so it is best for the
|
|
subsequent fireball phase. The images will be recorded on Galileo's tape
|
|
recorder as arrays of 7 by 7 or 8 by 8 images per frame.
|
|
|
|
A second scanning mode will be most useful for recording the time
|
|
history of the brief bolide flashes as the comet fragments plunge for a
|
|
couple seconds through Jupiter's upper atmosphere. Galileo's scan
|
|
platform will be moved so that the image of Jupiter drifts across the CCD
|
|
detector with the shutter open (through a narrow filter). The scans will
|
|
sacrifice one spatial dimension -- so the pictures won't be "pretty" -- but
|
|
the mode should permit the rise and fall of a bolide flash to be measured
|
|
every two-tenths of a second, or so. Diagonal scans across half of the
|
|
CCD are tentatively planned for events E and W and should be sensitive to
|
|
very faint phenomena (e.g. bolides from fragments as small as 100 m,
|
|
meteor storms, aurorae, etc.) as well as to bright phenomena. A more
|
|
efficient horizontal scanning approach is tentatively planned for fragment
|
|
K, but Jupiter will be superimposed on the flashes, so faint phenomena will
|
|
not be detected.
|
|
|
|
For five of the 19 impacts (tentatively C, F, G, P, and R), the camera
|
|
will not be used. Instead, the other scan platform instruments --
|
|
including the Near Infrared Mapping Spectrometer, the Photopolarimeter
|
|
Radiometer, and the Ultraviolet Spectrometer -- will try to record the
|
|
bolide and fireball phases of the impacts. Together, they cover a much
|
|
wider range of wavelengths than the camera, and often with better time
|
|
resolution. However, these instruments lack the camera's spatial resolution
|
|
and will record the impacts simply as enhancements to Jupiter's total
|
|
radiation at those wavelengths.
|
|
|
|
The remaining impacts (A, B[?], H, L, Q, S, T, U) will not be
|
|
observed by either Galileo's camera or most of Galileo's scan platform
|
|
instruments. For those events, the spacecraft will not be in sight of Deep
|
|
Space Network antennas on Earth; scan platform operations are not
|
|
permitted when engineers on Earth are not in contact with the spacecraft.
|
|
However, some monitoring of Jupiter's long radio-wavelength radiation by
|
|
the Plasma Wave Subsystem can be done during those events without
|
|
operating the scan platform; a low-rate PPR mode may alternate with PWS.
|
|
|
|
Most of the SL-9 impact data will be recorded on Galileo's tape
|
|
recorder for later play-back to Earth. It is expected that most of the
|
|
desired observations can be fit onto the tape recorder. The trick will be
|
|
to identify the important data, because only a few percent of it can
|
|
eventually be transmitted back to Earth over Galileo's small, low-gain
|
|
antenna given the limited allocations by the Deep Space Network. (Galileo's
|
|
large, high-gain antenna failed to open several years ago.) In order to
|
|
find the valuable data, Galileo engineers will rely on exact timings of
|
|
phenomena from Earth-based telescopic observers. They also hope to use
|
|
the measurements of the impact of an early fragment by the PPR to
|
|
calibrate the timings; if the absolute timing of that impact can be
|
|
measured, then the relative times of the remaining impacts will be
|
|
predictable to within a few minutes (or so we think).
|
|
|
|
It remains to be determined just how quickly Galileo will be able to
|
|
respond to late changes in the predicted (or observed) impact times. The
|
|
basic commands will be radioed out to the spacecraft a week or so in
|
|
advance of the mid-July commencement of impacts. They will tell the
|
|
spacecraft to observe (e.g. snap the camera shutter repeatedly) for an
|
|
hour on either side of the predicted impact times. Later information from
|
|
telescopic astrometry is expected to narrow the predicted impact times to
|
|
plus-or-minus 10 minutes during the final days, and it is hoped that late
|
|
commands can be sent up to Galileo to record data on the tape recorder
|
|
for plus-or-minus 20 minutes centered on such late predictions (it would
|
|
overtax the capacity of the tape recorder to record data for an hour or
|
|
two at each impact). Galileo may have the opportunity to change the
|
|
record times for the last several impacts based on observed times for the
|
|
early impacts. Finally, it is hoped that the actual times of the events will
|
|
become known to a couple of minutes, so that the appropriate parts of the
|
|
recorded data can eventually be returned to Earth.
|
|
|
|
The Galileo experiment will be GREATLY ENHANCED by the most rapid
|
|
communication of (a) updated, more accurate pre-impact predictions of
|
|
impact times from astrometry, (b) preliminary indications of when major
|
|
impacts may have occurred, and (c) refined estimates of impact times from
|
|
synthesis of all groundbased and spacebased data.
|
|
|
|
|
|
|
|
--
|
|
#include <standard.disclaimer>
|
|
_
|
|
Kevin D Quitt USA 91351-4454 96.37% of all statistics are made up
|
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|