Comets, minor planets and meteorites provide us with valuable information about the past history of the solar system. They belong to the most primitive samples of the primordial solar nebula. Over the past years, we can record a considerable increase of interest in these bodies.

The explosive increase in the number of published papers on planetary and satellite research in recent years has made it impossible to provide an adequate summary of progress in the field over a given three year period in the space allotted for this purpose. The problem is particularly acute for the current epoch - 1 January 1976 to 31 December 1978 - because it encompasses major missions to Mars and Venus by the United States and the Soviet Union, as well as a large number of exciting discoveries made from the ground.

Members of Commissions 16 and 17 have voted by a substantial margin (102 yes, 4 no, 1 abstention) to merge the two Commissions. The merger will take effect at the 17th General Assembly.

The Astronomical Council of the Academy of Sciences of the U.S.S.R. Two statistical models of regolith dynamics were investigated in cooperation with the Institute of Geochemistry. The dependence of material distribution upon depth and time and the dependence of crater distribution upon radius and shape of craters were studied. The theoretical hypsographic curve was drawn for the relief stipulated by cratering. The evolution time of the layer was shown to be the product of two factors, the first one depending only on the initial depth of deposit of the layer and on the size distribution of craters, and the second one corresponding to the extent of processing of the layer, depending on the size distribution and shape of craters (G.A. Leikin et al., Astron. Vestnik, [2], 1978).

The commission deeply regrets the deaths of our colleagues which were reported in the several circular letters issued during the last three years.

The past triennium has been noteworthy for several significant discoveries in the outer part of the solar system. The discovery of the rings of Uranus was inspired by the activities of Commission 20’s new Working Group on Occultations. Although the discovery of a probable Plutonian satellite has not yet been completely confirmed, the implication that Pluto’s mass is only 0.002 earth masses may make it desirable to consider whether Pluto should be relegated to minor-planet status. The orbit of Pluto is in fact not greatly dissimilar to that of the object classified as the new minor planet (2060) Chiron, which was found to have its aphelion near the orbit of Uranus and its perihelion just inside the orbit of Saturn.

L’afflux des résultats, évidemment lié aux techniques spatiales, améne à définir ici de façon plus stricte le champ de la Commission, en continuant d’ailleurs dans la tendance du rapport précédent: le terme “Lumière du Ciel Nocturne” ne s’applique plus qu’aux émissions et diffusions, de l’UV à I’IR, qui recouvrent la sphère cèleste entière. De plus, parmi les composantes telluriques, ne sont prises en consideration que celles dont l’obtention correcte de composantes astronomiques exige la connaissance. Les interpretations sont maintenues, surtout quant aux propriètès optiques des poussieres interplanètaires et interstellaires, mais il n’est plus possible d’inclure, entre autres, les observations non-optiques des grains interplanétaires, leur étude dynamique, ou le rayonnement IR du centre galactique.