Report of the working group on satellites for the Period July 1993 - June 1996 (J.E. Arlot) 1. Astrometric observations 1.1 Observations of the satellites of Mars During the three-year period all the observations of Phobos and Deimos made by the staff members of Goloseevo Observatory (Ukraine) since 1963 up to 1988 were processed using PPM catalog. About 2000 improved positions of the satellites and Mars have been obtained. These results are in preparation for publication. At the USNO, photographic observations were continued by D. Pascu with the 26-inch refractor at Washington D.C.. However, due to a shortage of 103aG plates from Kodak, a hiatus in the observations may occur for the satellites of Mars and also for the satellites of Jupiter and Saturn. 1.2 Observations of the galilean satellites of Jupiter 1.2.1 Direct observations of positions Nikolaev Observatory (Ukraine). During the period from 25.01.94 to 15.06.94, 33 photographic positions of the satellites were obtained with the zonal astrograph (D=154 mm, F=2042mm). The results of observations are included in the paper by G.K.Gorel' and L.A.Gudkova "Photographic observations of the satellites of Jupiter and Saturn in 1991-1994 (Ninth Report)". It contains 193 positions of satellites. The paper is not published as yet, but is available by application to the authors. During the period from May to July 1995, 16 absolute positions of the satellites with respect to FK5 were determined by photoelectric meridian observations with meridian circle equipped by CCD-microscopes. Pulkovo Observatory. Investigation of astrometric observations of the Galilean satellites with 26-inch refractor in 1976-1981 has been completed. The Jovicentric positions and mutual distances of the satellites have been obtained. The differences O-C computed by comparison with the Arlot's theory were used for investigation of occasional and systematic errors of observations and estimation of accuracy of the theory. The internal accuracy of observations is estimated by 0.03", the external errors being equal to 0.05"-0.17" depending on the distances between satellites. The longitude correction of J IV was determined and possibility of improvement of Jupiter's positions by measurement of satellites positions w.r.t. fundamental stars were investigated (Kisseleva 1996,Proceedings of IAU Symposium 172, S.Ferraz-Mello, B. Morando and J.E. Arlot eds, Kluwer Academic Press). U.S. naval Observatory (Washington D.C.) Photographic observations were continued and are sent to JPL for Galileo project and also to Bureau des longitudes for ephemeris development. 1.2.2 Photometric observations Mutual events of the galilean satellites observed in 1991 were reduced and catalogues of positions are in press (Kaas et al. in Astron. J., and Arlot et al. in Astron. Astrophys.). Eclipses of the galilean satellites were observed during the period 1990-1991 by Westfall and published in ALPOJ, 37, 154. 1.3 Observations of the faint satellites of Jupiter The results of observations of J VI, J VII, and J VIII made in 1987-1989 at Goloseevo Observatory (Ukraine), Kitab (Uzbekistan), and Majdanak (Uzbekistan) by the staff members of Goloseevo Observatory have been published (Izhakevich et al. 1994, Kinematika i Physica Nebesnykh Tel vol.10,n1, Kiev). From the Uppsala-ESO survey of asteroids and comets, Hernius et al.(1996, AASS, 115, 295) obtained photographic observations of JVI-XIII taken at ESO, Chile and at AAO, Siding Spring, Australia. Shelus et al.(1993, Astron. J. 106, 2573) obtained photographic observations of the faint outer satellites of Jupiter at the Mc Donald Observatory. Whipple et al. (1996, Astron. J. 112, 316) published their observations of J VI-XIII made during the 1994 and 1995 oppositions. CCD observations of J V and J XIV were made with the 61-inch astrometric reflector of the USNO at Flagstaff. 1.4 Observations of the satellites of Saturn 1.4.1 Direct observations of positions U.S. Naval Observatory (Washington D.C.) Satellites I-VIII are continuously observed photographically with the 26-inch refractor. CCD observations of satellites XII, XIII and XIV were made at Flagstaff with the 61-inch astrometric reflector (Rhode and Pascu 1993, BAAS 25, 1235 and 1994 BAAS 26, 1024). Pulkovo Observatory. Saturn's satellites I-VI and VIII were observed photographically with 26-inch refractor. 46 plates were taken with 6 or 7 exposures on every plate during the period from August to November, 1995. The planetocentric positions and mutual distances of the satellites were measured with internal precision on the order of 0.1" and external precision of 0.1"-0.2". The paper on the results of the observations is prepared. S I-S VI were also observed during the period from August to October, 1995 with CCD camera installed at 26-inch refractor. As a result about 100 mutual positions of the satellites have been obtained with equivalent internal precision of 0.05"-0.10" and external precision of 0.1"-0.2". Four mutual events were also observed, but with relatively low precision. Results of the observations are prepared for publication. Engelgardt Observatory. S IV, S V, and S VI were observed with astrograph (D=400mm, F=3780mm) during the period from September, 1994 to February, 1995 (19 plates) and from November 1995 to April 1996 (7 plates). The plates are processed. High altitude station of Engelgardt Observatory in Zelenchuk. S III, S IV, S V, S VI, and S VIII were observed with Zeiss astrograph (D=400mm, F=2000mm) in September, 1994 (29 plates) and in December, 1994 (11 plates). In a joint project between QMWC and the Royal Greenwich Observatory were reduced the CCD observations of Saturn's satellites made in La Palma at the oppositions in 1990,1991,1993 and 1994(Astron.Astrophys. 269,564-567,Research Note; Astron.Astrophys.(accepted for publication in the Main Journal). From 1968 up to 1995 nearly at every opposition, Y. Hatanaka of NAO has made photographic astrometric observations of 7 satellites of Saturn with the Zeiss 26-inch refractor (f=10 m). Although the observations with an unchanged system for such a long period of time are valuable, he has just published little results in Publ. National Astron. Obs. Japan, vol.4, No.2, 23-65 (1996). The opportunity of the ring plane crossing was taken in order to observe the faint inner satellites of Saturn using HST, infrared arrays at Palomar Observatory and CCD's at Pic du Midi Observatory, France and at LNA in Brazil. 1.4.2 Photometric observations During the ring plane crossing of 1995, extensive campaigns of observations of the eclipses by Saturn and of the mutual events were made. Considerable work on organizing observational campaign in the FSU for mutual events in Saturn's satellite system during 1995-1996 was fulfilled by the Celestial Mechanics Department of Sternberg Institute (GAISH), Moscow, headed by Dr.N.V.Emelyanov. At the Sternberg Institute (GAISH), South station in Crimea two events were observed photoelectrically with Zeiss-600: occultation of Dione by Rhea on 6.08.95 and eclipse-occultation of Encelade by Tethys on 14.09.95. At the Astrophysical Institute (Kazakhstan Republic) observations of events were made with 2 instruments: RZ-1000 (D=1000mm) at Assy station at the altitude 2750m and with RZ-600 (D=600mm) in Alma-Ata at the altitude 1450m. 15 events were observed altogether. Recording of the events were carried out with CCD-matrix, from 82 to 547 separate frames being taken during every event. A lightcurve for eclipse-occultation of Encelade by Tethys on 14.09.95 was obtained with CCD- matrix. Apart from the above observations several attempts to observe events in Saturn's satellite system were undertaken in Alma-Ata by visiting astronomers of GAISH, Engelgardt Observatory and Pulkovo Observatory. 11 mutual events were observed altogether with photoelectric photometer using the regime of photon counting, but unfortunately results of all these observations have low quality due to unmodelled variations of scattered light intensity and they hardly can be used for improvement of the satellite theories. Bureau des longitudes organized a campaign and 20 observations of eclipses and 94 observations of mutual events were made. Due to the difficulties of the reduction, only a part of these observations will be useful for astrometric purpose. 1.5 Observations of the satellites of Uranus D.H.P.Jones and D.B. Taylor are reducing La Palma CCD observations of the Uranian satellites made at the oppositions in 1990 and 1991. These are being analysed using a numerical integration. CCD observations were made by Veiga and Viera-Martins (1994, AASS 107, 551). The reduction of these data and of older photographic data were made using the motion of Uranus. They published also data from photographic plates (1994, AASS 107, 559) and CCD observations (1995, AASS 113, 557). Pascu, Rhode and Seidelmann made CCD observations of U-V with the 61-inch astrometric reflector at Flagstaff. HST astrometric observations of the inner satellites discovered by Voyager were reduced by Pascu et al.(1995, BAAS 186, 1302). 1.6 Observations of the satellites of Neptune Positions of these satellites were published by Veiga et al. in AASS 115, 319 and N-II was observed by Pascu, Rhode and Seidelmann at Flagstaff. 1.7 Miscellaneous A method of observation in order to observe faint satellites near bright planets are given by Veiga and Viera-Martins in 1995, AASS 111, 387. The working group on Natural Planetary Satellites has continued to gather observations in order to build a data base. This data base is established on the computer of Bureau des longitudes and is reachable by Internet at http://www.imcce.fr/ and contains data on the galilean satellites on line and other data on the ftp server at ftp.imcce.fr/pub/NSDC. 2. Theoretical works and comparisons to Observations 2.1 Miscellaneous Lieske (1993, Cel. Mech. & Dyn. Ast., 57, 473) published an algorithm for IAU North Poles and Rotation parameters of the planetary satellites. Kinoshita(1993 Cel. Mech. and Dyn. Astr. 57, 359) studied the motion of the orbital plane of a satellite due to a secular change of the obliquity of its mother planet. 2.2 Satellites of Mars Jacobson made a fit of the Morley/Sinclair theory to all available astrometric observations from 1877 to 1988 and the Mariner 9, Viking and Phobos spacecraft observations (1996, AAS Paper 96-140, AAS/AIAA Space Flight Mechanics Meeting, Austin, Texas. Smith et al. at the 25th Lunar and Planetary Science Conference published masses of Mars, Phobos and Deimos from the analysis of Mariner 9 and Viking Orbiter tracking data. 2.3 Galilean satellites of Jupiter The Sampson-Lieske theory of the motion of the Galilean satellites was fitted on mutual events observations and constants were published by Vasundhara et al. (1996, Proceedings of the IAU Symposium 172, Ferraz-Mello, Morando and Arlot eds, Kluwer Academic Press) and new ephemrides built. Same, Lieske (1994, JPL Eng. Mem. 314-545 and 1995, JPL Eng. Mem. 312-583) fitted the theory and built ephemerides. 2.4 Other jovian satellites Solovaya et al. (1994, Planetary and Space Science, 42, 8, 685) investigated the orbital motion of J8. Chapront and Rocher analysed observations and published ephemerides under a new representation of faint outer satellites of Jupiter JVI-JXIII (1996, Astron. Astrophys. in press). 2.5 Satellites of Saturn A Saturn's satellite pair Titan - Hyperion was studied by Kirsanov of the ITA. A rough numerical orbit of Hyperion was used as a reference one in Encke's method of numerical integration. The accuracy of such an integration was considerably higher than the straightforward one. 473 observations of Titan and 93 observations of Hyperion (from 1967 to 1981 time period) were considered in order to improve the satellites orbital elements. The mean O-C value for Hyperion is 0.47". The normality of the distributions of O-C values along and across the visible orbits of the satellites was studied. D.Harper (Queen Mary and Westfield College-QMWC,London University) and D.B. Taylor (Royal Greewich Observatory) on comparing the quality of observations of the satellites of Saturn made in the period 1874 to 1988 resulting from a fit of all data to the analytical theories(1994, Astron.Astrophys. 284,619-628). Predictions of the eclipses by Saturn and mutual events were made by Arlot and Thuillot (1993, Icarus 105, 427) and ephemeridesusing Dourneau's theory were provided to the observers. The staff members of the Sternberg Institute (GAISH), Moscow, under the leadership of Dr. N.V.Emelyanov have developed the integrated software package MONS-EPH for ephemeris provision of satellite observations (Emelyanov, 1996, Pis'ma v Azh., 22, 153). The most precise modern theories are realized in the package for majority of 59 natural satellites in the Solar system. For the rest, having no precise analytical theories, the approximate ones, sufficiently accurate for ephemeris calculations, are realized. The package is intended not only for calculation of positions of satellites for any moment of time, but also for calculation of circumstances of observations (positions of primary, the Sun and the Moon and its phase, etc.),for search of mutual events in the satellite systems and calculations of their circumstances. All these results are displayed graphically and in numerical form. The package is distributed among a number of observatories of the world. Using the package, the circumstances of all mutual events in Saturn's system in 1995-1996 were computed and published (N.V.Emelyanov, S.A.Gasanov, L.P.Nasonova, 1994. Circumstances for mutual phenomena of the Saturn's satellites in 1995-1996, Russian Astronomical Journ., v.71,n.5; N.V.Emelyanov, 1995 Peculiarities of mutual occultations and eclipses in the system of Saturn's satellites in russian, Astronomical Journ., 72, 604). Mutual events among Galilean satellites in 1997-1998 have been also calculated and corresponding ephemerides are in press. A redetermination of the minor satellite orbits (numerically integrated and precessing ellipse) from the original Voyager observations, astrometric observations through 1994, and 1995 HST observations was made by Jacobson (1995 Meeting of the American Astronomical Society Division on Dynamical Astronomy, Yosemite, Ca. in 1995 Bull. AAS 27, No.3, 1202-1203). A fit of a numerically integrated Phoebe orbit to astrometric from 1904 to 1994 and the Voyager 2 imaging observations was also made by Jacobson together with a fit of numerically integrated orbits for the eight major satellites to astrometric observations from 1971 to 1995, Voyager imaging observations, 1980 mutual event observations, and 1995 HST observations (1996 Meeting of the American Astronomical Society Division on Dynamical Astronomy, US Naval Observatory, Washington, D.C.. Vienne and Duriez (1995, Astron. Astrophys. 297, 588) fitted their own theory TASS to observations and made a comparison to Earth based observations. Message (1993, Celest. Mech. and Dyn. Astr. 56, 277) discussed the second order long-period motion of Hyperion. 2.6 Satellites of Pluto Bursa and Milan (1994, Earth, Moon and Planets 65, 3, 291) studies the effect of the tidal and rotational distorsion in the figures of Pluto and Charon. A search for small satellites of Pluto was made by Flynn et al. (1994, BAAS 187, 4218) using the HST archives. Studying the mutual events lightcurves, Young and Binzel (1994, Icarus 108, 219) made a new determination of radii and limb parameters for Pluto and Charon. Stern et al. (1994, Icarus, 108, 234) explore the possibility of satellites in the inner Pluto-Charon system by studying the dynamical and observational constraints. 3. Rings 3.1 Rings of Saturn Spahn et al. (1993, Cel. Mech. and Dyn. Astr. 57, 391) studied the gravitational influence of the satellite Pan on the radial distribution of ring-particles in the region of the Encke division in Saturn's ring. In her Ph. D. Thesis (1994) at Massachussets Institute of Technology entitled Stellar occultation studies of Saturn's rings with the Hubble Space Telescope (HST), A. Bosh analysed several occultations of the saturnian system observed either from ground-based observatories, from Voyager 1 and 2 and from HST. 3.2 Rings of Uranus and Neptune Photometry of the rings was made by Currie et al. (1994, BAAS 185, 43.14) from HST observations. French and Nicholson (1995, BAAS 186, 33.02) studied the edge waves and librations in the epsilon ring. The origin of the rings of Uranus and Neptune was studied by Colwell et al. (1993, Journal of Geoph. Res. 98, 7387). Hanninen and Porco (1994, BAAS 185, 65.05) studied the stability of the arcs of Neptune. Ferrari and Brahic made a systematic analysis and quantitative photometric study of Voyager 2 images of the neptunian narrow rings (1994, Icarus 111, 193). Colwell (1994, Planetary and Space Science, 42, 1139)studied the hypothesis of the disruption of small planetary satellites creating new narrow dusty rings around the planet Jupiter, Saturn, Uranus and Neptune.