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SUMMER 1994 TI,D VOLUME 17, NO.2 /\lMr R) [ NDWSLffiDR Comet Shoemaker-Levy 9 to Hit Jupiter Editor's Notes The Great Jupiter Comet Bash! Many changes have come to MIRA recently. For Get a front rorv seat to witness the cataclysmic one, the projected move to the new California State crash of Comet Shoemaker-Levy 9 into Jupiter. You University at Monterey Bay campus will become a re- are invited to The Great Comet Bash, a benefit event ality. Remodeling of the former Fort Ord building for MIRA, otr July 16th, starting at 6:00 p.m. at the scheduled for transfer to MIRA has gone to the draw- Monterey Conference Center. ing board (the computer screen?) at The Paul Davis You will be a part of an entertaining and educa- Partnership. Soon, MIRA's classrooms rvill surround a evening dinosaurs, music, good light- and greenery-filled atrium on the ground floor tional of astronoffiy, food, space art, and dance. of what was once an unprepossessing military struc- ture. The library and research facilities will occupy the second floor, and administrative offices and more Featured events include: research areas will take over the third level. At last, o Live pictures from the Space Telescope kstitute our many endeavors can be centralized in a single lo- o Historian Tom Logan on lost civilizations and comets cation, accessible to all, and convenient to other insti- o A children's comet art contest tutions committed to education and research. MIRA o Images from ground-based observatories sent via Internet of has some very exciting proposals under consideration the impact by a variety of public and private agencies. Our o Dr. Russell Coyle, "Dr. Disaster," onhow to casha check after Friends will be hearing more about these soon. The a comet impact funding for the remodeling project is now in the plan- o The latest nelvs and expectations from MIRA astrorpmers ning stages, under the able direction of Lynne Ches- o Astronomer William Hayden Smith on how a comet would ter, Ph.D. Progress reports are forthcoming. affect Earth' s atmosphere o Ongoing live updates from experts around the world There is a major change ahead for the Friends of o Live video from the Space Shutfle Columbia MIRA. Dennis Mar, the long-time Chair, is stepping o Music by local recording artist, Joe DeMaria down after six years of dedicated service. Dennis has o A space art exhibition been so reliable and resourceful, it is difficult to o An entertaining talk by dinosaur expert David Cudaback thank him adequately in so few words. But we try, o A dance performance by Fran Spector's dance troup anyway. Thanks, Dennis. We were fortunate to have o And more! Food and drink will be available your leadership. All attendees will receive a free commemorative The Friends will not be left leaderless, however. gift. Advance tickets are $25, $ 15 for Friends. Chil- Far from it! Into the breach steps Kim Cohan. Many dren under 16 free r,vith paid adult. At the door, tick- proceeds of you knorv Kim from his previous volunteer rvork ets $3 5 and $25 for Friends. All benefit for MIRA. He is also known for his experimentation MIRA. in computer graphics and communications, and his re- This event is sure to sell out. Call the MIRA office cent presentation at the Carl Cherry Foundation in at 37 5-3220 to order your seats which he demonstrated holograms and commentary via Internet magic. Kim's energJ and imagination will open new doors for the Friends of MIRA. Later in these pages, Kim introduces himself to our Friends in his own inimitable style. Kudos to MIRA Volunteers At this time, it is also appropriate to thank indi- Kim Cohan, Carl Cherry Center for the Arts board viduals whose support has made possible much of the member and President of the Friends of MIRA, or- good work done by MIRA. A 60mm Jason 311 con- chestrated the world's first live Internet video broad- stellation refractor telescope contributed by Richard cast of an art lecture. On June 4th, MIRA board Irmas of Carmel will be put to use in our educational members and volunteers Kim Cohan, Gary Love, program, which will surely be rapidly expanding. Doug McKinney, and Dennis Mar helped the Carl Cherry Foundation broadcast a fine art lecture on ho- Remember your That's it for now. to show support lography. Cohan, Love, and fellow MIRA board mem- for MIRA by attending our events. And keep an eye ber Lynne Chester helped underwrite the lecture and on Jupiter! accompanying art exhibit and hands-on workshop. Anne Cathey, Editor They said it couldn't be done, but they didn't count on MIRA volunteers ! On the coveF: JPL artist D. A. Feal\ impression of the impact of Comet Shoemaker-Lery 9 into Jupiter in mid-July, as ifviewedfrom a mythical satellite behindJupiter. Actually, Jupiterwill be millions of times brighter than the cometfragments before impact. Estimates of the brightness of the impact itselfvary enormously. COSMIC COMET COLLISION Dr. Whitney Shane The good news is that something will happen is a ring of small particles and dust at 1.8 radii, also which astronomers have never yet had the opportunity discovered by the Voyager. The planet is surrounded of observing. The bad news is that when it happens by a magnetic field (the magnetosphere) which is 100 it will be at a place times the radius of the where we cannot observe planet itself. Relativistic it directly. It is the colli- particles (mainly electrons sion of Comet Shoe- with speeds close to the maker- Levy 9 with Jupi- speed of light) are ter in July. Except for trapped in this field, and some unfortunate dino- \,ve can observe the syn- saurs around the year 65 chrotron radiation which million 8.C., ro one has they omit as they circu- ever been known to have late around the field observed the collision of lines. Charged particles, a comet with a planet, so like electrons, are readily no wonder the astrono- absorbed by dust, and the mers are excited. presence of a dust ring was predicted before its About Jupiter direct observation from an otherwise unexplained We know great deal a dip in the intensity of the about Jupiter, and this is synchrotron radiation. not the place to review all this knowledge, except for a few facts which will About Shoemaker-Levy 9 be of importance to us. Shoemaker-Levy 9 is .Jupiter is the most mas- certainly not your ordi- sive of the planets, more nary comet. As we than 300 times the mass know, comets move of the Earth, and this is around the Sun in eccen- important because the tric orbits. But not so in likelihood of a collision this case. Instead, comet increases with the mass Shoemaker-Levy 9 fol- of the target. Obviously lows an eccentric orbit the large radius, more around Jupiter. It is dy- than l0 times that of the namically very difricutt Earth, is also of impor- for a planet, even Jupiter, tance. Although Jupiter's to capture a passing ob- Artistb impression atmosphere is almost pure of the impact of Comet Shoemaker-LeW) 9 into ject, so this was in itself Jupiter a,s viewedfrom Earth (D.A. Feal, JPL). hydrogen ( 10000 parts H an extraordinary event. to one part of everything 'fhe comet was discovered else), it is not the hydrogen that we see but the con- in March, 1993, &s an elongated object. It grew in taminants, mainly ammonia gas, which condense into size and soon was seen to be resolved into a number the clouds which completely cover the planet. Jupiter of separate nuclei, of which now more than z0 have has no surface. The density and pressure just keep been counted. Orbit calculations showed that in July, increasing downward until a condition is reached 1992, the comet had passed within 1.4 radii of Jupi- where the gas has a density higher than anything on ter, r,vhich is rvell r,r,ithin the Roche limit. This is the earth. It is important for us to learn more about the distance at which a passing obj ect held together solely way in which the density, pressure, and temperature by self-gravitation (no sticky stufO will be disrupted behave with increasing depth. Jupiter is orbited by by tidal forces. It can be calculated from the mass of many satellites, as the Voyager observations demon- the planet and the density of the passing object, 8s strated, but we are interested only in the four Galilean was done by Roche 150 years ago in one of the clas- satellites, and particularly in Io, which orbits at a dis- sic exercises in celestial mechanics. When this hap- tance of only 6 Jupiter radii from the planet. There pens the individual fragments, which themselves must be held together by sticky stuff. all follow their indi- of the calculations, are quite accurate. And don't vidual, but very similar, orbits. There rvill, however, worry - there is no chance of a near miss be small differences in energy, resulting in slightly The biggest problem for the model makers is the different orbital periods, so that although all of the uncertainty regarding the physical properties of the fragments will eventually return to the same place, fragments. The masses are totally unknowr, and we they not get there at quite the same time. will all can only guess, by analogy with well observed comets This is why the fragments will be so well lined up like Halley, about their sizes.

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