ESO SL9 NEWS BULLETIN ===================== Issue : 8 Date : Sunday, July 17, 1994, 08:00 UT (10:00 CEST; 02:00 Chilean time) Items : 8-A: Plume from A-impact observed ! 8-B: The impact of fragment B 8-C: And then there was C 8-D: Impact timings 8-E. A night at ESO 8-A. Plume from A impact observed ! Gone are the secret worries of many astronomers ! Will the SL9 event be observable or not ? Now that this question has been definitively settled, we may come forward and admit that, very deep inside our hearts, we were afraid that nothing would happen at all ! To the surprise of many, a plume from the impact of the supposedly relatively small fragment A was observed at infrared wavelengths by several observatories. The first, exciting news about this came shortly after 20:30 UT, from the German/Spanish observatory at Calar Alto in southern Spain. It arrived in the form of a short email message over the "mail exploder" that was set up for exactly this purpose - to inform all observers about new and unexpected developments as soon as possible. The message (signed by Tom Herbst, Doug Hamilton, Jose Ortiz, Hermann Boehnhardt, Karlheinz Mantel, Alex Fiedler) was immediately read to the participants in the ESO all-night media event at the Headquarters in Garching. The observations were made with the 3.5-metre telescope using the MAGIC camera. The plume appeared at about nominal position over the limb at around 20:18 UT. It was observed using 1.7 and 2.3 micron methane band filters. It became brighter and soon outshone the light from the moon Io, on the other side of the disc of Jupiter. Calling La Silla by video phone at the same time, we quickly learned that a similar feature had indeed been observed there at 10 micron with TIMMI, but at first there was a slight confusion about the actual position of Io and the possibility that this feature may actually be the Jovian satellite. However, this question was quickly settled, and a few hours later, seven TIMMI images had been transferred by the link to Garching and placed on the ESO WWW Portal. Within 3 hours, there were more than 1000 accesses to these images from abroad ! The images show an absolutely unexpected, very rapid cool-down of the impact region. A preliminary analysis indicated that on the image obtained at 20:28 UT, the impact area is at 135 K, as compared to Jupiter which is normally at 115 K at this wavelength. The filter was the N2, i.e. 9.4 to 11 micron, and the scale was 0.6 arcsec per pixel. The observers were Benoit Mosser (DESPA/Meudon, France), Tim Livengood (National Research Council/NASA Goddard Space Flight Center) and Ulli Kaeufl (ESO). The TIMMI observations showed a rapid decrease in intensity of the plume: 20:22 UT - 1.000 (normalized intensity); 20:25 - 0.410; 20:28 - 0.218; 20:30 - 0.257; 21:16 - 0.036; 21:37 - 0.000 (spot extended and marginally visible). The spot was seen to be extended by 4 - 5 pixel, i.e., 2.5 -3.0 arcsec, parallel to the limb. No observations through any of the filters detected a bright spot on the disc after this time, indicating that ammonia was not projected into the stratosphere by the impact; this means that the impactor probably did not reach the cloud top. Observations were also made with the MPI/ESO 2.2-metre telescope and the IRAC2B camera. Here, Klaus Jockers obtained a beautiful series of images of the plume at 2.2 micron, as it moved across the disc. It became obvious that the plume persisted much longer at this shorter wavelength than in the 10 micron observations made with TIMMI. Uri Carsenty (DLR, Berlin) reported tha images were obtained with the fast CCD camera (from DLR) with Methane narrowband filter (centered on 873 nm). They clearlly showed the site of impact A as a bright spot that was not present on the reference images obtained during the previous nights. This feature was continuously observed until about 01:30 UT, when it was very close to the western limb of Jupiter. Calar Alto and La Silla soon turned out to be only two of several sites that observed this incredible event. From La Palma, Pierre Olivier Lagage, Juan A. Belmonte, Goran Olofsson, Ana Ulla, S. Larson, H. Campins, F. Moreno, and A. Molina informed that the plume had been observed with the 2.56-metre Nordic Optical Telescope with the Saclay CAMIRAS Camera. A bright spot at 10 microns at the southeast of the planet was seen at about 20:25 UT. This spot was brighter than any pixel of Jupiter and disappeared within about 30 minutes. A similar effect was seen at 2.16 microns with the new IAC IR camera at the Telescopio Carlos Sanchez of Teide Observatory. Some two hours later, a black dot was seen in the visible video image of Jupiter, exactly at the same position where the TCS was detecting a sort of dusty bright spot. The South Pole Infrared Explorer (SPIREX), a 60 cm telescope, detected the plume at 2.36 microns. At 20:25 UT it was still brighter than Io. Its brightness diminished rapidly during the next two minutes, but it remained visible at this wavelength (CO filter) for 20 minutes. This information came from M. Hereld, H. Nguyen (at S. Pole Station), B. Rauscher, S. Severson (Astronomy & Astrophysics Center, University of Chicago). Further confirmation of the very bright plume at 2.3 and 1.7 microns came from the Cerro Tololo Interamerican Observatory. Here, John Spencer and Darren DePoy used the OSIRIS instrument with the CTIO 4-metre telescope. The plume was brighter than Jupiter's polar caps at 2.36 microns. There were also two fainter spots which were visible closer to the equator at 1.7 microns - these might be a normal meteorological phenomenon though. A beautiful image was obtained by the HST in the optical region, at wavelength 4100 A. It showed the impact area, just after it became visible at the limb, as a circular feature, surrounded by a ring-shaped formation. It actually looked as a "hole" or "crater" in the atmosphere, but the depths were not known yet. Slit spectra of the impact area were obtained at La Silla by Therese Encrenaz and Rita Schulz who worked at the NTT with IRSPEC, and also by John Spencer and Darren DePoy, who obtained spectra with OSIRIS at the CTIO 4-metre telescope, near the meridian. They also watched the impact site rotate off the limb at 2.36 microns. It persisted till about 01:50 UT, despite a predicted disappearance at 01:20 UT, indicating major lateral spreading and/or great altitude. 8-B. THE IMPACT OF FRAGMENT B The B fragment was much brighter than A in images of the comet train and was hence expected to have a more dramatic impact. The unexpectedly clear detections of the A impact in the infrared and also at shorter wavelengths from HST hence led to expectations of something even more dramatic when the B fragment hit Jupiter about seven hours later. Conditions at Chile were then less good with significant cloud but there were high hopes of detecting the impact in the infrared. This impact was visible from many US observatories but unfortunately not from HST which was on orbits taking it through the "South Atlantic Anomaly" where much higher radiation levels make most observations impossible. Soon after the expected time it became clear that this impact was in fact considerably less prominent than the first one as brief reports of failures to detect anything started to come in. The first arrived at 4:04 UT from Palomar where imaging at 2.35 micron and 7.9 micron with the 5-metre telescope had failed to see anything up to 03:55 UT. Soon afterwards the similar lack of success at ESO, with both the 3.6-metre and 2.2-metre telescopes (observing at 9 micron and 2.2 micron respectively) was reported to the "mail exploder" distributing electronic mail to the observers around the world. These were followed by negative reports from the Cerro Tololo Interamerican Observatory (CTIO) using the 4-metre telescope and a detector working at 1.7 micron and 2.3 micron, these observations, from a site close to La Silla were also affected by cloud. Nothing was seen from Stewart Observatory in Arizona, USA either with imaging at 2 micron or spectroscopy covering a wavelength range from 2.0 - 2.4 micron. Similar conclusions were reported by the Apache Point Observatory using the 3.5-metre. This instrument is the second generation of the SPIREX camera at the South Pole which reported a positive detection of A in the same filter. However, not all results were negative. The largest optical telescope in the world, the W. M. Keck Observatory (10-metre) on Mauna Kea Hawaii, recorded a faint but clear plume at the expected position starting at 02:56 UT and fading around 03:13 UT. This detection was confirmed soon afterward by spectroscopy at 3.5 micron using the UK Infrared Telescope (UKIRT) on the same mountain where a fivefold brightening around the expected time of the collision was detected at the limb of the planet. It faded over 90 minutes. Observations were made in a narrow "L" band around 3.35 micron. These weaker detections suggest that the impact was not totally different in type, but just much weaker than that of A. Was this because the B-fragment was smaller than A, or did it plunge deeper into the atmosphere so that there was less to be seen above the impact site. Fortunately, there are still another 19 or so fragments that may be observed, so perhaps this central question may be solved. 8-C. AND THEN THERE WAS C Two impacts associated with fragment C were detected at 2.34 micron using the CASPIR infrared camera on the ANU 2.3 m telescope, and IRIS on the 3.9 m Anglo-Australian Telescope at Siding Spring Observatory, Coonabarabran, Australia. The first event began at 06:24 UT, approximately 38 minutes earlier than predicted, and produced a feature which is approximately 2.4 arcsec across, located 45 S, and twice as bright as the south polar cap. The second, and much stronger, event was seen at the limb at 07:20 UT. This event brightened appreciably during the first 5 minutes and then faded to the brightness of the first event after 10 minutes. Both features were still visible one hour after the initial impact. Near-infrared filter photometry of the features is now being carried out at the 2.3 m telescope, and the AAT will continue K band drift-scan spectral mapping observations at a resolving power of 300. The report is by Peter McGregor and Mark Allen (ANU 2.3-metre) and David Crisp, Vikki Meadows, Stuart Lumsden and Steve Lee (AAT 3.9-metre). Beginning at 07:15 UT, the NASA/Infrared Telescope Facility observed the development of a bright spot on Jupiter associated with the impact of fragment C. The NSFCAM near-infrared camera took 0.9-sec integrations every 3.6 seconds at a wavelength of 2.248 +/- 0.011 microns. Starting at 06:51 UT, the camera recorded Io and Europa, searching for a flash; no flash was obvious but the data are yet to be photometrically reduced. At 07:15 the telescope moved to Jupiter, and detected both the remnant of the A impact, with a surface brightness similar to that of the south polar hood at this wavelength, and a dim spot from fragment C. By 07:18, site C was considerably brighter than site A, but by 07:28 site C had faded to about site A's brightness, and continued to fade until about 07:40, when it was considerably fainter. Reported by the NASA/IRTF Comet Collision Science Team. 8-D. IMPROVED IMPACT TIMES Paul Chodas and Don Yeomans (JPL) have provided the final list of updated impact parameters. In this connection, it looks as though ESO on July 15.0 got the final observations of most of the fragments. The impact times are within a few minutes of those in the previous table, dated July 11. In particular, the time for A is 2.1 minutes later, and C and F are 2.7 minutes later. The time for U moved 4 minutes earlier. Despite heroic efforts, observers were unable to image fragments A and B later than July 13. The impact time uncertainties for most of the fragments are now down in the 6 - 10 minute range (95 percent interval). ------------------------------------------------------------------------------- Fragment Impact 1-sig Jovicentric Meridian Angle Orbit Date of Date/Time Unc. Lat. Long. Angle E-J-F Ref. Last Data July (UTC) (min) (deg) (deg) (deg) (deg) (July UT) --------------h--m--s---------------------------------------------------------- A = 21 16 19:59:40 5.5 -43.13 178 64.48 98.72 A25 13.0 B = 20 17 02:54:13 4.1 -43.16 70 63.82 99.18 B20 13.2 C = 19 17 07:02:14 3.7 -43.37 218 65.24 98.12 C18 14.0 D = 18 17 11:47:00 4.7 -43.45 30 65.58 97.85 D19 14.0 E = 17 17 15:05:31 3.1 -43.47 150 65.76 97.72 E35 14.2 F = 16 18 00:29:21 4.0 -43.56 132 64.52 98.57 F26 13.2 G = 15 18 07:28:32 3.1 -43.59 23 66.63 97.07 G32 14.2 H = 14 18 19:25:53 3.1 -43.73 96 66.83 96.89 H31 14.2 K = 12 19 10:18:32 3.1 -43.80 275 67.76 96.21 K33 15.0 L = 11 19 22:08:53 3.4 -43.91 344 68.18 95.88 L34 15.0 N = 9 20 10:20:02 4.9 -44.29 66 67.77 96.10 N22 15.0 P2= 8b 20 15:11:55 4.6 -44.61 244 66.68 96.80 P20 15.0 Q2= 7b 20 19:31:43 -44.35 39 68.78 95.37 Q1= 7a 20 19:59:10 4.5 -44.06 55 69.20 95.12 Q37 15.0 R = 6 21 05:25:56 4.6 -44.07 37 69.44 94.94 R32 15.0 S = 5 21 15:10:22 4.4 -44.16 30 69.80 94.67 S42 15.0 T = 4 21 18:03:45 11.5 -44.99 137 67.34 96.26 T16 4.1 U = 3 21 21:48:30 12.8 -44.43 272 68.81 95.33 U17 8.0 V = 2 22 04:16:53 8.1 -44.43 146 69.50 94.83 V18 15.0 W = 1 22 07:57:36 5.2 -44.15 278 70.44 94.21 W33 15.0 ------------------------------------------------------------------------------- 8-E. A NIGHT AT ESO Yesterday evening, more than 100 media representatives gathered in the main auditorium at the ESO Headquarters in Garching to experience the first impact(s) of comet SL9 on Jupiter. There were 10 TV companies, several with mobile satellite transmission stations; nobody at ESO can remember such an interest in a scientific theme connected to this organization. The evening began with the showing of a specially produced video film, showing the connection between ESO, the comet and the astronomers in a very symbolic and unusual way. The young filmmakers, Herbert Zodet and Irakli West, received much acclamation for their oeuvre. Following a general introduction and update, we talked to Dave Laney at Sutherland over the phone and then with several of the observers at La Silla. It was a pity that a complete power failure at Entel/Chile made it impossible to transmit slow TV-images of the speakers during this session, dealing mostly with the astronomers' intentions and hopes, just before they went to their telescopes. Another connection to the Space Telescope Science Institute brought up-to-date information from Keith Noll and Renee Prange about this night's observations with this facility. And just before the A-impact, predicted to happen almost exactly at 22:00 CEST, we got fine images of Jupiter from a 36-cm telescope on the roof. Deep silence during the critical period around the A-impact, but nothing was seen (as expected !?). After this "negative" experience, some of the audience left, but the persistent members of the audience were soon thereafter rewarded by an unsually intense couple of hours during which we learned about the observation of a plume over the A impact site by many telescopes (item 8-A). Email messages and images came in from all directions and were projected on the video screen; phone contact with the observers at La Silla reflected the great enthusiasm, we all felt by being present at this historical moment. The TIMMI images were transferred and placed on the ESO WWW Portal. Within the next three hours, they were accessed more than 1000 times, mostly from the U.S.A., but also from most countries in Europe. A B/W press photo of the event at its most intense moment was produced during the morning and distributed as ESO PR Photo SL9J/94-09. The expectations were high for the B-impact, at 04:54 CEST in the morning. And then there was another surprise, as nothing was seen with TIMMI. The weather at La Silla deteriorated and the observations had to stop at 05:35 CEST. Reports from other observatories confirmed this negative result, and we ended the session 06:00 CEST. Soon thereafter, we learned about the detection of the B-plume from Keck and UKIRT. And then we started to prepare this eighth issue of the ESO SL9 Bulletin to be ready for the Press Conference at 11:00 CEST. ---------- 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