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1994-04-15
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Background Material for Science Teachers
JULY 1994 -- Periodic Comet Shoemaker-Levy 9 Collides with Jupiter
Cover: Comet Shoemaker-Levy 9 is expected to collide with Jupiter
in July 1994. From this historic event, scientists hope to learn
more about comets, Jupiter, and the physics of high velocity
planetary impacts.
For a period of about six days centered on July 19, 1994,
fragments of Comet Shoemaker-Levy 9 are expected to collide with
Jupiter, the solar system's largest planet. No such event has ever
before been available for study. The energy released by the larger
fragments during impact will be more than 10,000 times the energy
released by a 100-megaton hydrogen bomb! Unfortunately for
observers, the collisions will occur on the night side of Jupiter,
which also will be the back side as seen from Earth. The
collisions can still be studied in many ways, nevertheless, by
spacecraft more advantageously located, by light of the collisions
reflected from Jupiter's satellites, and by the effects of the
impacts upon the Jovian atmosphere. (The impact sites will rotate
into view from Earth about 20 minutes after each collision.)
Stupendous as these collisions will be, they will occur on the far
side of a body half a billion miles from Earth. There will be no
display visible to the general public, not even a display as
obvious as a faint terrestrial meteor. Amateur astronomers may
note a few seconds of brightening of the inner satellites of
Jupiter during the impacts, and they might observe minor changes
in the Jovian cloud structure during the days following the
impacts. The real value of this most unusual event will come from
scientific studies of the comet's composition, of the impact
phenomena themselves, and of the response of a planetary
atmosphere and magnetosphere to such a series of "insults".
This booklet offers some background material on Jupiter, comets,
what has and possibly will happen, and how scientists propose to
take advantage of the impact events.
Contents
1. What Is a Comet?
2. The Motion of Comets
3. The Fragmentation of Comets
4. The Discovery and Early Study
of Shoemaker-Levy 9
5. The Planet Jupiter
6. The Final Orbit of Shoemaker-Levy 9
7. The Collisions
8. How Can These Impacts and Their
Consequences Be Studied?
9. What Do Scientists Expect
to Learn from All of This?
Appendices
A. Comparative Tables
B. The K-T Event
C. The Probability of Collisions with Earth
NOTE: Diagrams and illustrations refered to in the text will be
produced as GIF files in the near future. When they become
available, these text files will be reposted with them.
Acknowledgments:
This booklet is the product of many scientists, all of
whom have cooperated enthusiastically to bring their best
information about this exciting event to a wider audience. They
have contributed paragraphs, words, diagrams, slides, and
preprints as well as their critiques to this document, which
attempts to present an event that no one is quite sure how to
describe. Sincere thanks go to Mike A'Hearn, Paul Chodas, Gil
Clark, Janet Edberg, Steve Edberg, Jim Friedson, Mo Geller, Martha
Hanner, Cliff Heindl, David Levy, Mordecai-Mark Mac Low, Al
Metzger, Marcia Neugebauer, Glenn Orton, Elizabeth Roettger, Jim
Scotti, David Seal, Zdenek Sekanina, Anita Sohus, Harold Weaver,
Paul Weissman, Bob West, and Don Yeomans -- and to those who might
have been omitted. The choice of material and the faults and flaws
in the document obviously remain the responsibility of the author
alone.
The writing and production of this material was made possible
through the support of Jurgen Rahe and Joe Boyce, Code SL, NASA,
and of Dan McCleese, Jet Propulsion Laboratory (JPL). For help in
the layout and production of this booklet, on a very tight
schedule, additional thanks go to the Design Services Group of the
JPL Documentation Section.
All comments should be addressed to the author:
Ray L. Newburn, Jr.
Jet Propulsion Laboratory, MS 169-237
4800 Oak Grove Dr.
Pasadena, CA 91109-8099
--
_/ _/ _/ _/ _/ _/ _/ _/ David M. Seidel
_/ _/ _/ _/ _/ _/ _/ Educational Services Specialist
_/ _/ _/ _/ _/ _/ _/ _/ Jet Propulsion Laboratory
_/ _/ _/ _/ _/ _/ _/ _/ _/ _/ _/ Public Education Office
_/ _/ _/ _/ _/ _/ _/ _/ _/ _/ _/ "Just say Know"