Report of the Working Group on Satellites for the period 1975-1978 (S. Ferraz-Mello) A - GENERAL Meetings on observations and ephemerides of planetary satellites have been held each year at the U.S. Naval Observatory; the 1977 meeting coincided with the centennial of the discovery there of the satellites of Mars, and the proceedings of a special colloquium on these bodies (including some papers on astrometry and dynamics) are contained in Vistas Astron. 22, part 2. A symposium and workshop on the motions of natural and artificial satellites was held in Austin in December 1977; the proceedings will be published by the University of Texas Press. B - NEW AND UNCONFIRMED SATELLITES The most spectacular event of the triennium has been the discovery of an elongation of Pluto, probably due to a satellite that has been temporarily designated 1978 P 1, by J.W. Christy with the 155cm astrometric reflector at the U.S. Naval Observatory's Flagstaff Station. The elongation was confirmed photographically at the Cerro Tololo and McDonald Observatories and visually at Mauna Kea (IAU Circ. Nos. 3241 and 3286; Astron. J. 83, pp.1005-1008). The observations suggest a satellite 2-3 magnitudes fainter than Pluto in an orbit inclined at 105 deg. with respect to the plane of the sky. Seven approximate positions, including two separations, were obtained in 1978, as well as eight prediscovery observations in 1965, 1970 and 1977. The period is consistent with the lightcurve period of Pluto (6.3867 days), and the mean distance from the planet is about 20 000 km. L. Andersson (Bull. Am. Astron. Soc. 10, p. 586) remarks that a solution with the ascending (rather than the descending) node near 170 deg. fits the observations best and suggests that eclipse phenomena should occur during the next few years. Analysis by J.W. Fountain and S.M. Larson of observations of faint images near Saturn appearing on exposures obtained with the Lunar and Planetary Laboratory's 154cm reflector during the 1966 passage of the earth through the ring plane indicates the existence of another satellite of about the same brightness as A. Dollfus' satellite Janus and in a similar orbit; the objects are perhaps major members of an extended ring (Icarus 36, pp. 92-106). On the other hand, K. Aksnes and F.A. Franklin (ibid. 36, pp. 107-118) point out that, while the observations may suggest that satellites do exist near the rings (although the possibility of ring knots cannot be excluded), their orbits cannot be uniquely determined; they propose that Janus and the Fountain-Larson object be given the temporary designations 1966 S 1 and 1966 S 2. Efforts should be made to clarify the situation during the earth's 1979-80 ring-plane passage. Aksnes and Franklin also rediscuss the case of Pickering's 1904 satellite Themis and conclude that all evidence for its existence has vanished. No additional observations have been reported of 1975 J1 (the probable fourteenth satellite of Jupiter). Attempts to recover it at McDonald and Palomar appear to have been unsuccessful. C - OBSERVATIONAL PROGRAMS AND TECHNIQUES Astrometric observations of the established satellites have been reported by 13 observatories. The program at McDonald included observations with some regularity of all the faint satellites of Jupiter (J V-XIII) and of Saturn I-IX. G.F. Benedict, P.J. Shelus and J.D. Mulholland improved the techniques for plate measurement and reduction using a microdensitometer (18.031.297; 18.099.241; 19.099.509; Astron. J. 83, pp. 999-1002). Over 550 observations of the satellites of Mars, the Galilean satellites, Saturn II-VI and Saturn VIII were made at the Pulkovo Observatory by T.P. Kiseleva and others (20.100.031; Byull. Inst. Teor. Astron. 14, N¡ 8). The Galilean satellites and Saturn I-VIII were also observed at the Leander McCormick Observatory by P.A. Ianna and P. Seitzer, who obtained more than 400 exposures at the 1976-77 and 1977-78 oppositions. Ianna also observed Uranus III and IV and Neptune I at Mount Stromlo. At Kazan some 400 positions of the Galilean and Saturnian satellites were obtained under the direction of I. Chugunov, and at Nikolaev about 100 plates were taken by V. Voronenko, G. Gorel' and F. Kalikhevich (20.041.049). Some 50 exposures of the satellites of Mars were obtained by D. Pascu at the U.S. Naval Observatory at the December 1975 and January 1978 oppositions, and the Pascu neutral-density-filter-spot technique was also used by R.L. Walker, Christy and R.S. Harrington to obtain positions of the satellites of Uranus and Neptune I (Astron. J. 83, pp. 838-844). Roemer obtained a few exposures of Jupiter XIII and Neptune II (Steward 229-cm reflector). D.B. Campbell et al. (Icarus 34, pp. 254-267) have published Doppler shifts of the radar echoes from the Galilean satellites on 22 nights in 1975 and 1976. D - ORBITAL STUDIES AND THEORETICAL INVESTIGATIONS Some 4900 observations of the satellites of Mars distributed at more than 20 oppositions were used by Shor (14.042.032; 18.097.203) to determine new orbital elements, secular variations and the figure of Mars. A better representation of the observations is achieved as compared to earlier solutions. The acceleration of Phobos is found to be (21.4 deg ± 2.2) x 10-9 day-2. The resulting longitudes represent well the positions derived from Mariner-9 TV data. Radio-tracking data associated with the encounters between the satellites and the Viking Orbiter 1 spacecraft have been analyzed by E.J. Christensen et al. (Geophys. Res. Lett. 4, pp. 555-557) and by R.H. Tolson et al. ( ibid. 4, pp. 551-554). Their results are consistent with the combined value of (1.63 ± 0.12) x 10-8 Mars masses for the mass of Phobos. J.H. Lieske revitalized Sampson's theory for the Galilean satellites by removing algebraic errors, introducing some neglected effects, allowing for non zero-amplitude librations and providing final results as analytic functions of 49 arbitrary constants of integration and physical parameters (19.099.507). The series of photometric eclipses observed at Harvard from 1878 to 1903 has been combined with other post-1903 photometric eclipses in order to evaluate the parameters of the theory ( Astron. Astrophys. 65, pp. 83-92). B. Brown (Celes. Mech. 16, pp. 229-259) removed short- period terms by Kamel's averaging technique and studied the long- period behavior of the orbits. A comprehensive analysis by G.W. Null (18.099.182) of Doppler data from Pioneer 10 and 11 during their encounters with Jupiter yielded improved values for the masses of the Galilean satellites and the harmonic coefficients of Jupiter. Theoretical investigations by Aksnes (IAU Colloq. No 41), Ferraz-Mello (ibid.), E.N. Lemekhova (14.099.239) and J.L. Sagnier are in progress. An introductory book by Ferraz-Mello on the Dynamics of the Galilean Satellites is in press at the University of Sao Paulo. Final analyses of the 1973 series of mutual phenomena of Jupiter's satellites have been published by Aksnes and Franklin (17.099.218) and by T. Nakamura (17.099.220). Aksnes and Franklin (Icarus 34, pp. 188-193), and also J.-E. Arlot (Astron. Astrophys. Suppl. 34, pp. 195-197), have provided predictions for the mutual phenomena to occur in 1979. From 31 available observations of Jupiter XIII covering nearly five revolutions about Jupiter, Aksnes (Astron. J. 83, pp. 1249-1256) determined a new orbit and computed an ephemeris from 1978 to 2000. T.V. Bordovitsyna and L.E. Bykova completed their numerical studies and determined new orbital elements for Jupiter VI-IX. New methods for solving ill-conditioned systems were used, and a new determination of the mass of Jupiter was made (Astron. Geod. Tomsk 6, pp. 32-41; ibid. 6, pp. 42-46; Byull. Inst. Teor. Astron. 14, No 7). Y. Kozai (18.100.204) published an extension of his early work, with the masses of Saturn II, IV and VIII and the oblateness parameters of Saturn being recomputed using correct expressions for the forced eccentricity and mean longitude of S II and accurate expressions for the perturbations of the orbit of S VI due to S VIII. The results are m2 = 1.3 ±Ê0.4Ê) x 10-7, m4 = (1.85 ± 0.04) x 10-6, m8 = (0.10 ± 0.08) x 10-5, Saturn masses. Also, the mass of SV, m5 (0.9 ± 0.2) x 10-5, is derived from the observed secular motions of six satellites. Y. Hatanaka (IAU Symp. N¡ 81) improved the orbital elements of SVIII. From observations taken in pairs since 1874, M. Rapaport (18.100.207) improved the mean motions of Saturn I-V. The values show agreement with Kozai's early work but not with the values proposed by H.A. Garcia (08.100.015). Rapaport also compared existing theories of S VIII with observations, finding it necessary to consider the resonance with S VI (Astron. Astrophys. 62, pp. 235- 238). A. T. Sinclair (20.100.501) fitted recent photographic observations to existing theories of S III-VI and to his theory of S VIII (12.100.214) and derived improved orbital elements. From a gravitational model fitted to observed secular motions, W.I. McLaughlin and T.D. Talbot (19.100.020) determined m5 = (4.8 ±0.8) x 10-6 and the mass of the ring mR = (6.2 ± 2.4) x 10-6 Saturn masses. A new theory of resonant satellite orbits developed by W.H. Jefferys and L.M. Ries has been applied to S II and S IV. With the participation of Mulholland they have now completed the discussion of observations for the determination of the constants of integration. L. Blitzer (Celes. Mech. 16, pp. 87-95) has applied spin-orbit theory to the 4:3 resonance between S VI and S VIII. A. W. Harris and C.F. Peters (19.100.504; 20.100.019), and also J.G. Porter and E.R. Delo (Handb. Br. Astron. Assoc. for 1977 and 1978; 20.100.512), provided predictions for two eclipses of S VIII by Saturn's rings in 1977-78. Aksnes and Franklin (Icarus 34, pp. 194- 207) have published predictions for the mutual phenomena of S I-VII during 1979-80. R. Greenberg compared observations of Uranus V with theory and obtained for the product of the masses of Uranus I and II an upper limit of about 10-9 Uranus masses (18.101.004). Uranus V is 10 deg ahead of the longitudes extrapolated from D.W. Dunham's elements, and this is the expected effect of U I and II. Dunham plans to update his orbital elements for the satellites of Uranus. Ephemerides for Neptune II have been published yearly by Aksnes (17.101.006; 19.101.028; IAU Circ. No 3219).