ESO SL9 NEWS BULLETIN ===================== Issue : 3 Date : Tuesday, July 12, 1994, 12:00 UT (14:00 CEST; 08:00 Chilean time) Items : 3-A: New impact timings 3-B: Calculating the orbits 3-C: The individual comet fragments 3-D: Hubble Space Telescope observations 3-E: Galileo Imaging Plans 3-F: First fragments enter the magnetosphere 3-A. NEW IMPACT TIMINGS Here is the July 11 edition of the "Predicted Impact Parameters for Fragments of P/Shoemaker-Levy 9" by Paul Chodas, Don Yeomans and Zdenek Sekanina (JPL/Caltech) and Philip Nicholson (Cornell). The orbit solutions for these predictions incorporate several new highly-accurate measurements reduced using the Hipparcos star catalog. Except for fragment V, the predicted impact times are holding steady, within 5 minutes of those in the previous table, dated July 5. The impact time for fragment V, however, jumped 17 minutes later. There is little new data on fragments T and U because they are so faint and difficult to observe; their orbit solutions are not improving much. The impact time 95 percent uncertainties for most of the fragments are now down in the +-10 minute range. The angle E-J-F is the Earth- Jupiter-Fragment angle at impact; values greater than 90 deg indicate a farside impact. All impacts will be just on the farside as viewed from Earth; later impacts will be closer to the limb. According to these predictions, the only impact certain to occur during a satellite eclipse is K=12 with Europa eclipsed. The better the orbital accuracy, the better will be known in advance the moments of impact and the location of the impact sites on Jupiter. The latter is particularly important for the attempts to detect changes on the surface: the smaller the areas to be searched, the greater are the chances that changes may indeed be found. The full table with all parameters is available in the SL9 information area of the ESO WWW Portal. ----------------------------------- Frag- Impact 95 percent Angle ment Date/Time interval E-J-F July (UT) (+- min) (deg) ------------h--m--s---------------- A 16 19:57:34 16.4 98.87 B 17 02:54:02 13.6 99.21 C 17 06:59:25 14.0 98.27 D 17 11:45:30 15.0 97.95 E 17 15:05:00 11.2 97.71 F 18 00:26:39 12.0 98.67 G 18 07:27:36 9.6 97.10 H 18 19:25:55 9.4 96.88 K 19 10:17:50 9.6 96.24 L 19 22:07:07 10.2 95.95 N 20 10:21:15 13.4 96.03 P2 20 15:09:51 13.2 96.88 Q1 20 19:59:29 10.8 95.08 R 21 05:24:17 12.4 95.00 S 21 15:09:53 11.8 94.69 T 21 18:05:50 26.4 96.18 U 21 21:52:39 29.0 95.20 V 22 04:14:43 20.6 94.96 W 22 07:56:53 14.4 94.25 ----------------------------------- 3-B. CALCULATING THE ORBITS The calculation of the orbits of the individual fragments is quite complex, since it must include the gravitational effects from the Sun, Jupiter and the Jupiter moons. At this moment, about 100 hours before the first impact, the locations in space of the first fragments to reach Jupiter are known to within a few hundred kilometres, but during the next days, their rate of motion will accelerate as they approach the giant planet. A small error in the location now will therefore mean a much larger uncertainty in its location just before the impact. This is why it is important to continue to observe the positions of the comet fragments during the next days. As an example, the speed of fragment A, relative to Jupiter, increases from about 7 km/sec (July 12.0), 9 km/sec (July 14.0), 13 km/sec (July 16.0), to nearly 60 km/sec at impact (July 16.826). According to Syuichi Nakano, the impact of fragment A occurs about 2 minutes later because of the gravitational attraction of the large moons. 3-C. THE INDIVIDUAL COMET FRAGMENTS At least twenty fragments of comet SL9 will hit Jupiter during the next ten days. It has proved very difficult to predict the effects which they will actually cause, mainly because their properties (mass, structure, composition, etc.) are very poorly known. Nevertheless, some studies have been made to cast more light on the colliding bodies. At La Silla, Rita Schulz and Joachim Stuewe (Max-Planck-Iinstitute fuer Aeronomie, Katlenburg-Lindau, Germany) carried through a short observational programme with the 3.5-metre New Technology Telescope (#2 in the ESO SL9 Brochure) with the aim of studying the individual fragments. The observations were performed as foreseen during two nights on June 30 - July 2. The astronomers obtained deep B,V,R,I images which show some colour differences between the individual nuclei. These observations were hampered by the proximity of Jupiter which caused a strong backround gradient, but indicate that fragments may have different properties. Of great interest is also that their long-exposure spectroscopy (in the blue and red arms of the EMMI instrument) with a total of more than 3 hours exposure has possibly revealed some CN emission. This would be the first time that a gaseous component has been observed in comet SL9, but this result must be confirmed after a further careful reduction of the new data. Some fragments are brighter than others and it is generally believed that the brightest ones are also the largest and will therefore cause the greatest effects on impact. However, the brightness is only a measure of the amount of dust around a fragment; a big and compact (and therefore heavy) fragment with little dust may appear fainter than a small and less heavy fragment with a greater dust production. This means that we cannot predict with certainty which of the impacts will be the most dramatic. Olivier Hainaut (ESO-Chile) has provided the following, relative brightnesses (integrated image intensity, with G = 1.00) of the "early" fragments, measured on the red-sensitive CCD exposure (and therefore directly indicating the amount of dust) that was obtained with the NTT on July 11: A (0.14); B(0.26), C (0.25), D (0.16), E (0.57), F (0.30), G (1.00), H (0.69), K (0.88) and L (0.69). 3-D. HUBBLE SPACE TELESCOPE OBSERVATIONS The following schedule for HST observations was provided by Ron Baalke of JPL. It includes HST observations during the week leading up to the impacts and the impact week itself. Unless otherwise indicated, all observations are for imaging with the WFPC-2 (Wide Field/Planetary Camera-2). i) Q fragment on 11 July, 19:14-21:41 UTC, ii) G fragment on 14th July, 08:24-10:49 UTC, iii) FOS spectroscopy of the G fragment on 14th July, 11:37-14:04 UTC, iv) S fragment on July 14th, 14:50-17:16 UTC, v) K fragment on 18th July, 15:17-16:09 UTC, vi) L fragment on 19th July, 13:49-14:38 UTC, vii) Q fragment on 20th July, 07:32-10:00 UTC, viii) S fragment on 20 July, 17:09-17:59 UTC. This is a partial list and excludes observations of Jupiter itself. 3-E. GALILEO IMAGING PLANS This item is a condensed version of two articles by Clark R. Chapman, leader of the Galileo imaging team's SL9 investigation. The Galileo spacecraft, headed for Jupiter orbit in late 1995, will be the only observatory capable of actually "seeing" 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. The imaging data will be acquired both as direct imaging and also as scans where one dimension of the information will be sacrificed in order to record better the time evolution of the events. This latter 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. 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. The Galileo sequence that contains the observations of SL9's impact with Jupiter has been completed, approved, and transmitted to the spacecraft. The July 5th updates by Chodas and Yeomans were used to develop "tweaks" to the times that data will be recorded on to tape. The shutter will be operated for about 2 hours around each of the 6 events to be observed (fragments D,E,K,N V and W), but only about one hour of data will be recorded on tape for each event. It is hoped that some information about the collisions of other fragments may be extracted from data stored on the spacecraft after the events have finished. Details will depend on what other observers find. More complete information may be found at JPL's WWW Comet Shoemaker- Levy Homepage (URL: http://newproducts.jpl.nasa.gov/sl9/sl9.html). 3-F. FIRST FRAGMENTS ENTER THE MAGNETOSPHERE According to the Voyager 1 30-day Science report, (Science 204, 983), the Jovian magnetopause extends to about 5.7 million km from the planet in the comet approach direction. The magnetopause distance varies with the solar wind, but fragment H is now this distance from Jupiter so it's likely that the first fragments of the comet have now entered the magnetosphere. It is time to start looking for changes due to charging and stripping of the cometary dust. (John R. Spencer, Lowell Observatory, USA). ---------- This daily news bulletin is prepared for the media by the ESO Information Service on the occasion of the July 1994 collision between comet Shoemaker-Levy 9 and Jupiter. It is available in computer readable form over the ESO WWW Portal (URL: http://http.hq.eso.org/eso-homepage.html) and by fax to the media (on request only). News items contained therein may be copied and published freely, provided ESO is mentioned as the source. ESO Information Service European Southern Observatory Karl-Schwarzschild-Strasse 2 D-85748 Garching bei Muenchen Germany Tel.: +49-89-32006276 Fax.: +49-89-3202362