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D/1993 F2
Shoemaker-Levy 9

Hubble Space Telescope image of C/1993 F2 (Shoemaker-Levy 9) exposed on 1994 May 17
Copyright 1994 by H. A. Weaver and T. E. Smith (Space Telescope Science Institute), and NASA

A NASA Hubble Space Telescope (HST) image of comet P/Shoemaker-Levy 9, taken on May 17, 1994, with the Wide Field Planetary Camera-2 (WFPC-2) in wide field mode. This required 6 WFPC exposures spaced along the comet train to include all the nuclei. The image was taken in red light.

Discovery

     Carolyn S. and Eugene M. Shoemaker and David H. Levy (Palomar Observatory in California) examined a pair of photographs exposed on 1993 March 24 as part of a routine asteroid survey. Although the team had already discovered numerous comets during the previous few years, these photographs held a most unusual object. Each plate revealed a comet which resembled a dense linear bar, with a faint, wispy tail. At a later date, they said their initial reaction was that the comet appeared "squashed." The comet was reported to the appropriate authorities, and was named Shoemaker-Levy. A more formal name of periodic comet Shoemaker-Levy 9 was later given to the comet when astronomers realized it completed one orbit around the sun every 17 years and was therefore classed as a short period comet. This was the ninth short-period comet discovered together by the Shoemakers and Levy. While the comet's initial appearance was certainly something new and unusual, the comet's location was also of interest. Brian G. Marsden's announcement of the comet on IAU Circular 5725 included his remark that "The comet is located some 4 degrees from Jupiter, and the motion suggests that it may be near Jupiter's distance." As orbits were computed it was soon realised that the comet was actually in orbit around Jupiter. An independent discovery was reported by O. Naranjo (Merida), who found the comet on a photograph exposed on March 26.2.
     In the days following the comet's discovery, additional images of the comet were found on earlier plates taken elsewhere. K. Endate (Kitami) found an image on a photograph exposed on March 15.6. S. Otomo (Otomo Observatory) photographed it on March 17.6. The team of E. Helin, K. Lawrence, and C. Brewer (Palomar Observatory) found images exposed on March 19.4.

Historical Highlights

  • The Orbit: IAU Circular 5726 (1993 March 27) contained the first orbits determined for this comet. B. G. Marsden used 9 positions obtained on March 24, 26, and 27, and computed a parabolic and an elliptical orbit. Both orbits indicated rather close approaches to Jupiter, with the parabolic indicating a close distance of 0.31 AU on 1993 March 30 and the elliptical indicating a distance of 0.04 AU on 1992 July 28. With the help of the March 15 prediscovery position and further observations up to April 1, Marsden announced on IAUC 5744 (1993 April 3) that the parabolic solution "was no longer viable" and provided a revised elliptical solution indicating a close approach of 0.007 AU from Jupiter on 1992 May 16. He added that a tidal breakup presumably required an approach to 0.001 AU. After another month and a half of positions had been obtained, Marsden provided a greatly improved orbit on IAUC 5800 (1993 May 22). This indicated the comet passed 0.0008 AU from Jupiter on 1992 July 8.8 UT, at which time it was torn to pieces. Even more interesting was that the comet would collide with Jupiter during July of 1994. Later calculations revealed the 21 pieces of this comet would strike Jupiter during the period of 1994 July 16 to 22.
  • Perhaps the best set of observations obtained during this comet's apparition was that provided by Akimasa Nakamura (Kuma Kogen Astronomical Observatory, Japan). Using a 0.60-m telescope he determined the total magnitude, measured the length of the comet, and provided magnitude estimates of several of the nuclei. A small sample includes the following observations obtained during the first six months of 1994.
           January 8.85: The total magnitude was estimated as 15.1 and the coma length was 2.8 arc minutes. He said the fragments were oriented on a line extending from PA 64° to PA 244°. Nuclear magnitude estimates: G=18.8, H=19.1, K=18.8, L=19.0, Q=18.7, R=19.3, S=19.6.
           April 13.73: The total magnitude was estimated as 15.2 and the coma length was 5.2 arc minutes. He said the fragments were oriented on a line extending from PA 63° to PA 243°. Nuclear magnitude estimates: G=18.7, H=19.0, K=18.8, L=19.1, Q=18.4, R=19.6, S=19.5.
           June 1.55: The total magnitude was estimated as 15.0 and the coma length was 6.8 arc minutes. He said the fragments were oriented on a line extending from PA 64° to PA 244°. Nuclear magnitude estimates: F=19.6, G=18.7, H=19.0, K=18.9, Q=18.3, R=19.1, S=18.7, W=19.7.
  • Some Interesting Impact Results: Here are a few of the most interesting announcements.
           --The Kuiper Airborne Observatory detected water within the "splash phase" of Fragments G and K.
           --Near-infrared Spectroscopy was obtained at the United Kingdom Infrared Telescope at Mauna Kea, Hawaii. In a paper by T. Y. Brooke, G. S. Orton, D. Crisp, A. J. Friedson, and G. Bjoraker it was revealed that carbon monoxide was detected at the site of the L event about four hours after impact.
           --Detection of sodium, iron, magnesium, calcium, and manganese was made during the impact of fragment L, while sodium D was found during the impact of Q1.
           --Observations of the impacts of A, H, and Q were made at the Serra La Nave Station of the Catalina Astrophysical Observatory by C. Blanco, G. Leto, and D. Riccioli. Photometric monitoring of Europa and Io revealed slight brightenings at the time of the A and Q events.
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