SL-9/JUPITER ENCOUNTER - SPECIAL Comet Shoemaker-Levy 9 Collides with Jupiter THE CONTINUATION OF A UNIQUE EXPERIENCE R.M. WEST, ESO-Garching After the Storm Six Hectic Days in July eration during the first nights and, as in other places, an extremely rich data The recent demise of comet Shoe­ ESO was but one of many profes­ material was secured. It quickly became maker-Levy 9, for simplicity often re­ sional observatories where observations evident that infrared observations, es­ ferred to as "SL-9", was indeed spectac­ had been planned long before the critical pecially imaging with the far-IR instru­ ular. The dramatic collision of its many period of the "SL-9" event, July 16-22, ment TIMMI at the 3.6-metre telescope, fragments with the giant planet Jupiter 1994. It is now clear that practically all were perfectly feasible also during day­ during six hectic days in July 1994 will major observatories in the world were in­ time, and in the end more than 120,000 pass into the annals of astronomy as volved in some way, via their telescopes, images were obtained with this facility. one of the most incredible events ever their scientists or both. The only excep­ The programmes at most of the other predicted and witnessed by members of tions may have been a few observing La Silla telescopes were also successful, this profession. And never before has a sites at the northernmost latitudes where and many more Gigabytes of data were remote astronomical event been so ac­ the bright summer nights and the very recorded with them. Brief reports from tively covered by the media on behalf of short evening visibility of Jupiter just over some of these programmes are brought such a large and interested public. the western horizon made such obser­ in this Messenger issue. The fact that a Now that the impacts are over and vations next to impossible. In addition, significant amount of observing time was the long and tedious work to reduce the it is most gratifying that legions of ama­ allocated after the main event was over, many data has begun, time has come to teur astronomers immediately went into turned out to be a major blessing, and look back and try to appreciate what re­ action when it became known that the some of the most interesting data were ally happened. This may be easier said changes on Jupiter could be perceived obtained during the period immediately than done, for few of the many actors even with very small telescopes. following the last impact on July 22. were able to experience the full spec­ During the week of the impacts, press It is not yet possible to estimate the trum of associated events. Most of the conferences were held at many obser­ total amount of SL-9 observational data astronomers who were directly involved vatories; ESO arranged a series of very now available at observatories all over in the observations hardly had time to well attended media events in Garch­ the world, but it may well run into many do anything else, and the interested lay­ ing and in Santiago de Chile. A day­ tens, perhaps hundreds of Gigabytes. men who watched on their TV screens to-day chronicle of what happened dur­ One of the most urgent problems is now the frantic activity all over the world were ing this period may be found in the to get an overview of all these data so not in the best position to get a bal­ "ESO SL-9 News Bulletin" of which a that observers from different sites will be anced overview from all of this. At this total of 14 issues were prepared be­ able to establish effective collaborations. moment, two months later, more has be­ tween July 10 and 26. The full text, It has also become evident that in or­ come known about the many observa­ as well as many images and graph­ der to understand the very complex pro­ tional programmes, and the first indica­ ics may still be obtained from the ESO cesses around the impacts, in particu­ tions of the exciting science that will ul­ WWW Portal (http://http.hq.eso.org/eso­ lar the detailed evolution of the plumes timately result from the enormous data homepage.html) or via anonymous ftp ("fireballs") that rose above the impact sets have begun to emerge. (ecf.hq.eso.org; directory: pub/sI9-eso­ sites, it will be necessary to intercompare The 22nd General Assembly of the In­ images). data from many different instruments with ternational Astronomical Union, held dur­ The observing possibilities were best a variety of techniques, ranging from ing the second half of August in The from the southern hemisphere and, by the high-resolution, extremely detailed Hague (The Netherlands), offered the good fortune, the weather in South Africa UV and visual images of the Hubble first opportunity to learn in more detail and Australia was very co-operative dur­ Space Telescope, to "movie-like" image about the outcome from the very suc­ ing the critical week. It was less so in sequences obtained with infrared instru­ cessful, world-wide observational efforts. Chile, where La Silla, Cerro Tololo and ments like TIMMI, and long-exposure, Two four-hour sessions were ably orga­ Las Campanas were effectively clouded high-dispersion spectra of these plumes nized at very short notice by Catherine out during the latter part of the impact obtained with more classical spectro­ de Bergh, David Morrison, Mike A'Hearn period. Long series of excellent obser­ scopic equipment. and Alan Harris. More recently, a meet­ vations were also made from La Palma ing of the La Silla observers took place on and Calar Alto (Spain), as well as from Much Hard Work Ahead September 12 at the ESO Headquarters Hawaii and observatories in Japan. Al­ in Garching. though details are still lacking, it is ap­ The observed effects were extremely Here follows a short and most certainly parent that the programmes at many ob­ spectacular, from the incredibly bright quite incomplete overview of the current servatories in other countries were also "fireballs" (or "plumes") which rose above status of the SL-9 observations and their very successful. However, a complete list the limb of the planet, to the intricate great potential for new knowledge, based of all SL-9 observations has yet to be and changing forms of the resulting "pan­ on the presentations during these meet­ compiled. cake" clouds, of which several - to the ings. At ESO, ten telescopes were in op- greatest surprise of many astronomers- 28 are still visible at the end of September, although less prominent than before. Until now, most observational pro­ Impact Times for Fragments of Comet grammes have not progressed much be­ yond a purely phenomenological descrip­ Shoemaker-Levy 9 tion of what was seen. However, it is also the task of all astronomical research to The following list of impact times (UTC times received at Earth, i.e. light-time corrected) was prepared by Don Yeomans and Paul Chodas (JPL) in early August 1994. progress far beyond such a simple de­ scription; the ultimate goal is of course to understand the physical processes be­ Fragment Date Prediction (h:m:s) Accepted impact time hind the event. This calls for "reduction" and 1 (J error and "interpretation" of the data. The first A July 16 20:00:40 20:11:00 (3 min) is a long and complicated procedure, in­ B July 17 02:54:13 02:50:00 (6 min) volving different types of calibrations in C July 17 07:02:14 07:12:00 (4 min) 11:47:00 11:54:00 (3 min) order to "clean" the raw data from all D July 17 E July 17 15:05:31 15:11:00 (3 min) possible, extraneous effects and to ex­ F July 18 00:29:21 00:33:00 (5 min) tract the quantitative information that is G July 18 07:28:32 07:32:00 (2 min) needed to arrive finally at a global under­ H July 18 19:25:53 19:31:59 (1 min) J July 19 02:40 Missing since 12/93 standing of what really happened. K July 19 10:18:32 10:21:00 (4 min) For this reason, most observers have L July 19 22:08:53 22:16:48 (1 min) so far only been able to answer a few of M July 20 05:45 Missing since 7/93 the many questions which are now be­ N July 20 10:20:02 10:31:00 (4 min) P2 July 20 15:16:20 15:23:00 (7 min) ing eagerly asked from all sides. Having P1 July 20 16:30 Missing since 3/94 been treated to real fireworks of "real­ 02 July 20 19:47:11 19:44:00 (6 min) time science" and "quick-shot guessti­ 01 July 20 20:04:09 20:12:00 (4 min) mates" (greatly facilitated by the incredi­ R July 21 05:28:50 05:33:00 (3 min) S July 21 15:12:49 15: 15:00 (5 min) bly successful initiation during this event T July 21 18:03:45 18:10:00 (7 min) of the "astronomy information super­ U July 21 21:48:30 21:55:00 (7 min) highway", especially via internet), and V July 22 04:16:53 04:22:00 (5 min) having been confronted (not to say W July 22 07:59:45 08:05:30 (3 min) "spoiled"!) with hundreds of impressive pictures of mushroom clouds in the In setting forth the accepted impact times given in the final column, the priority of the southern hemisphere of Jupiter, the me­ various available techniques is as follows: dia and the public now keep asking when 1.