__________________________________________________________________________ T H E O L E R O E M E R M E S S E N G E R _______________________________________________ JJJJ C G JJJJJJ I E JJJJ __________________________________________________________________________ Newsletter of the International Jupiter Watch Satellite Discipline E-mail issue 5 November 23rd, 1993 Editor and Discipline Leader: John Spencer Voice: (602) 774-3358 Lowell Observatory Fax: (602) 774-6296 1400 W. Mars Hill Rd. Internet: spencer@lowell.edu Flagstaff, AZ 86001 ------------------------------------------------------------------------------ EDITORIAL COMMENTS At the DPS meeting I took over the role of Satellite Discipline Leader from Jay Goguen, and I will also continue to produce this newsletter. So send all your suggestions and complaints to me from now on! Most of this newsletter is a condensed update of Shoemaker-Levy impact news, plus a report from DPS. PLEASE let me know if you submit a paper that relates to the surfaces of the satellites of Jupiter, or if you have other news, and I will mention it here. Also, let me know if you have firm observing plans for the upcoming apparition, so that others can coordinate with you if that is useful. ------------------------------------------------------------------------------ SHOEMAKER-LEVY IMPACT Glenn Orton, Atmospheres Discipline Leader, has been issuing frequent e-mail updates on the status of predictions and preprints: to avoid duplication it's simplest to subscribe to his mailing list (contact Glenn at "go@orton.jpl.nasa.gov" or "go@uli.jpl.nasa.gov"). I'll include things in this forum that are specifically satellite related. For now, here's a brief summary of the current situation: FUNDING: Combining NSF and NASA proposals for the Shoemaker-Levy funding initiative, and eliminating duplicate proposals, a total of $5,300,000 has been requested in 86 proposals, compared to the $1,500,000 that is available. PUBLICATIONS: Geophysical Research Letters is planning a special issue devoted to predictions of impact phenomena, with a submission deadline of February 1, 1994. Contact Hunter Waite, (hunter@swri.dnet.nasa.gov, (210) 522-3493), for details. PREPRINTS: Tidal Disruption of Periodic Comet Shoemaker-Levy 9 and a Constraint on Its Mean Density Alan P. Boss (DTM, Carnegie Institution of Washington) Submitted as a Note to Icarus Comet Shoemaker-Levy-9 Impact on Jupiter Thomas J. Ahrens, Toshkiko Takata, John D. O'Keefe, Glenn S. Orton Submitted to Nature Preprint requests: tja@seismo.gps.caltech.edu Tidal Disruption and the Appearance of Periodic Comet Shoemaker-Levy 9 Zdenek Sekanina, Paul W. Chodas, and Donald K. Yeomans Submitted to the Astronomical Journal Preprint requests: zs@sek.jpl.nasa.gov (This preprint has a detailed consideration of the probability of favorable satellite configurations for observing the flash from each impact.) Observing the Flash When Comet Shoemaker-Levy 9 Collides with Jupiter G. B. Field and A. Ferrara Preprint requests: gfield@cfata3.harvard.edu WORKSHOP: A planning workshop is scheduled for January 10-11, 1994, at the University of Maryland. Contact Mike A'Hearn or Lucy McFadden for more information. They can be reached by E-mail at : c1993e@astro.umd.edu FILTERS: I am coordinating ordering of custom filters for observations of the impact and its effect on the Jovian atmosphere. Considerable savings are possible with bulk orders, and I have received about 15 indications of interest so far. If you are interested, please contact me as soon as possible, being as specific as you can about the wavelengths, bandpasses, and sizes that you require. SCIENCE: At the DPS, two lines of evidence were presented suggesting that the Shoemaker/Levy fragments might be bigger than recent estimates of c. 1 km diameter. Weaver et al. thought it likely that light from the brighter nuclei was distinguishable from the coma contribution in the HST images of the comet, giving estimates of about 4 km for the diameter of the brightest nucleus, assuming a Halley-like albedo. Also, new models of the 1992 tidal breakup (see the above preprint by Sekanina et al.) showed that the diameter derived from the length and orientation of the nuclear train was critically dependent on the effective time of breakup, and the best match was obtained if the pieces separated about 1.5 hours after perijove, giving an initial diameter of at least 9 km. The best current predictions of impact times of individual fragments are still uncertain by about +/- 0.3 days (1-sigma). Impact flash brightness estimates by Ahrens et al. suggest that for a 2 km impactor the post-disruption fireball will have a brightness of about 10^24 ergs/sec for of order 1 minute, with an effective temperature of about 1000 K. Greatly improved impact time estimates, good to an hour or so, should be available shortly, when the comet emerges from behind the sun and new astrometry is possible. We will then finally know what impacts will be visible from where, and what satellites will be available as reflectors. IMPACT FLASH REFLECTION REFLECTIONS: If Ahrens' estimate of the power and temperature of the post-disruption fireball are correct, we can determine the brightness of the flash at various wavelengths. Here I've calculated the brightness relative to reflected sunight at Io, assuming that Io is perfectly placed (behind Jupiter but not occulted by it), and that the fireball is a 1000 K blackbody with a total power of 10^24 ergs sec-1: Wavelength, (Flash brightness on Io)/ Flash Microns (Reflected Sunlight) Magnitude --------------------------------------------------- 0.5 3e-10 29.4 1.0 4e-5 15.7 1.5 2e-3 11.3 2.0 0.01 9.1 2.5 0.03 7.9 3.0 0.07 7.1 4.0 0.15 6.2 5.0 0.23 5.6 The short-wavelength brightnesses are underestimates, because some of the radiation will be at temperatures higher than 1000 K, but the extreme wavelength dependence and major advantage of longer IR wavelengths is apparent. Flash monitoring in the L (3.5 microns) and M (4.8 microns) windows should be a high priority! Flashes on Amalthea will be 10 times brighter relative to reflected sunlight, but 6.2 magnitudes fainter in absolute terms. For Europa, flashes will be 3 times fainter relative to sunlight than on Io, and 1.5 magnitudes fainter in absolute terms. Note, by the way, that Amalthea's orbital period is 12.0 hours, so it is at the same place in its orbit at a given time every night from a particular site. Some longitudes will be able to look for flashes off Amalthea every night, while other longitudes will never be able to use Amalthea. For those with IR spectrographs, particularly if they are photometrically accurate, a nice experiment would be to take low spectral resolution, high time resolution, spectra of a suitable satellite during an impact, in a wavelength range that includes both a methane band and adjacent continuum. Analysis of methane band depths in the flash would give important information on the altitude of the fireball as a function of time. This could possibly by done with a long-slit system by scanning the satellite along the slit during a single long exposure... Because much of the fireball may be seen through the methane-rich ambient atmosphere, there is danger in using methane filters to supress Jupiter light while looking for flashes off the satellites, though for Amalthea there is probably no choice about this. The flash brightness is likely to be attenuated in methane bands, making both detection and interpretation more difficult. ------------------------------------------------------------------------------- DPS REPORT Here's my subjective summary of highlights of Galilean satellite surface results presented at DPS. Results that were presented in similar form at the Io conference are omitted here. Christophe Dumas et al. showed the value of Fourier deconvolution of infrared images of Io in revealing the presence of hot spots: 5 or 6 hot spots can be resolved on the best deconvolved images. Jay Goguen et al. presented a 10-km resolution 3.8 micron image of Loki obtained by tomography from multiple Europa occultation lightcurves during the 1991 brightening, which showed two narrow N/S fissures 50-100 km long. Howell explored some of the uncertainties inherent in these tomographic reconstructions. Clarke et al. showed HST disk-resolved 1600-3300 A spectra of the Pele region and an SO2-rich area on Io. Ballester et al. presented an analysis of the signature of SO2 gas in similar HST spectra. Burnett et al. showed that laboratory sputtering of sodium sulfate gave high yields of molecular sodium species which might explain the presence of molecular sodium in the magnetosphere. Meade and Jakosky presented thermophysical models of the trapping of SO2 frost in Io's surface layers. Hapke suggested that Io's low atmospheric pressure was best explained by a thin ephemeral layer of surface SO2. Ingersoll and LeBeau demonstrated the possibility of a nonvolatile night-time atmosphere, chiefly of SO, on Io. Moore et al. pointed out possible sublimation-collapse features on Io and Europa. Spencer \etal\ showed the shallow, sharp, and still unidentified 5770 A absorption feature on Ganymede visible in their recent CCD spectra. Pascu et al. presented BVRI photometry of Thebe and Amalthea, showing leading/trailing asymmetries in color and brightness. At the IJW Steering Group meeting, we discussed the extent to which observations of Saturn, particularly the upcoming series of mutual satellite events during the ring-plane crossing, should be included in the IJW. I will cover news on the satellite events briefly here, but people who are seriously interested in observing them should contact Phil Nicholson (nicholso@astrosun.tn.cornell.edu) who is coordinating ring-plane crossing activities outside the formal structure of the IJW. ------------------------------------------------------------------------------ ICY GALILEAN SATELLITES CONFERENCE San Juan Capistrano Research Institute, February 1-3, 1994 Nothing new to report, except a reminder than abstracts are due shortly, on December 3rd. ------------------------------------------------------------------------------ OBSERVING PLANS It's a bit early for the 1994 season, and I haven't received notice of any observing plans yet, except that I can tell you that I'll be obtaining CCD spectra of the Galilean satellites, especially Ganymede, from the Lowell 72", on January 21-26 1994 UT, in further pursuit of the 5770 A absorption feature. ------------------------------------------------------------------------------ PUBLICATIONS IN (OR EMERGED FROM) THE PIPELINE Here come the first batch of SL9 publications... Sekanina, Z. (1993). Disintegration phenomena expected during collision of Comet Shoemaker-Levy 9 with Jupiter. Science, 262, 382-387. Kerr, R. (1993). Planetary science - Jupiter hits may be palpable after all. Science, 262, 505. Melosh, H. J., and P. Schenk (1993). Split comets and the origin of crater chains on Ganymede and Callisto. Nature 365, 731-733. Scotti, J., and H. J. Melosh (1993). Estimate of the size of comet Shoemaker-Levy 9 from a tidal breakup model. Nature 365, 733-735. -------------------------------------------------------------------------------