The activity of the Minor Planet Center continued generally to increase during the triennium. This report covers the period 2008 July 1 to 2011 October 12, and the phrase “during the triennium” in this report should be understood to mean this period.

The CSBN meeting held in Rio de Janeiro on August 11 was attended by just six members, including Pam Kilmartin as the acting chair, and several visitors. Since there was not a quorum of members, it was not possible to make any decisions. But there was a good discussion on many topics, from which several points emerged that should be more fully discussed by the whole committee during the next few months:

The activity of the Minor Planet Center continued generally to increase during the two triennia covered by this report, principally because of the continuing success of the surveys for near-earth objects. Chief among these has been the Lincoln (Laboratory) Near-Earth Asteroid Research Project, or LINEAR, which is credited with the discovery of slightly more than half of all the minor planets that have been numbered, although since 2005 the Catalina Sky Survey and Mount Lemmon Survey in Arizona and the Siding Spring Survey in New South Wales (all three of which, together with the long-lasting Spacewatch Survey, are operated from the University of Arizona) have come to dominate the field. The total number of observations of minor planets in the MPC's files more than doubled from 14.1 million in mid-2002 to 30.9 million in mid-2005, with almost another doubling, to 55.4 million, in mid-2008.

The Working Group on Planetary System Nomenclature (WG-PSN) develops, maintains and publishes guidelines for naming natural satellites of planets and surface features on all solar system bodies except Earth. When required the WG approves lists of new nomenclature, with accompanying explanatory notes, based on the established guidelines. Approved names are immediately added into the Gazetteer of Planetary Nomenclature. Objections based on significant, substantive problems may be submitted within a 3-months period, and will be ruled on by Division III.

A total of 701 comets received names between July 2005 and June 2008. Comets observed only from the SOHO and STEREO missions, as well as further comets recognized from the long-defunct SOLWIND satellite, accounted for 520 of these names.

From Director Dan Green's report, following this report, it is obvious that the Central Bureau for Astronomical Telegrams (CBAT) continues its excellent work. The Electronic Telegrams (CBETs), established in the previous triennium, have become the regular means for fast communication, with the Circulars providing the official and archival record of discoveries and designations. It is regretted that subscriptions to the printed Circulars continue to decline, but inevitable in this age of electronic communication.

A total of 16 among the new IAU members have asked to join Commission 20; they are: Jerome Berthier, Nicholas J. Cooper, Marco Delbò, Romina P. Di Sisto, Michael W. Evans, Tetsuharu Fuse, Ludmila Hudkova, Yurij N. Krugly, Elena N. Polyakhova, Zhanna Pozhalova, Alessandro Rossi, Qi Rui, Jonathan D. Shanklin, Slawomira E. Szutowicz, Gino Tuccari and Hong-Suh Yim. Moreover, two requests to join the Commission have been received by astronomers that are already IAU members: Peter De Cat and Ricardo A. Gil-Hutton.

The meeting was attended by six from the WG (K. Aksnes, J. Blunck, G. Consolmagno, B. Marsden, R. Schulz, V. Shevchenko) and two from the Task Groups (D. Morrison, J. Watanabe). Also the incoming WG members E. Bowell and R. Courtin, as well as some guests, attended.

The president proposed the following for the coming triennium: Alan C. Gilmore president, and Nikolai N. Samus vice-president. Members: Brian G. Marsden, Daniel W. E. Green, Syuichi Nakano, Elizabeth Roemer, Jana Tichá, Hitoshi Yamaoka, Kaare Aksnes. Supernova group representative: Hitoshi Yamaoka was invited on to the OC to provide a link with supernova observers.

After a brief discussion it was agreed that this membership is well distributed in terms of geography, gender, and fields of planetary work.

The Working Group was formed at the request of the Board of DivisionIII and approved by the IAU Executive committee in March 2004. This was in recognition of the fact that discoveries in the Trans Neptunian region were repeatedly raising the question of “what is a planet”. The task of the WG was to investigate the options available and give indications of the level of support and opposition for each if more than one option was emerging.

The recognition of the extensive population of bodies in the outer Solar System has been arguably the most significant discovery about the Solar System from groundbased observations during the twentieth century. Our understanding of the transneptunian population is still quite flawed in its details, although a plausible picture has been emerging.

This report is a continuation of three earlier reviews (Marsden 1996a, 1996b, 1998) that included a summary of our orbital knowledge of the Kuiper Belt. Presented at conferences held in the middle of 1994, 1995 and 1996, respectively, these reviews showed the steadily developing picture of a system dominated by the platinos, librating in the 2:3 mean-motion resonance with Neptune, and the cubewanos, a somewhat more distant population of nonlibrating objects with low orbital eccentricities. The existence of a 3:4 Neptune librator and a 3:5 Neptune librator was also suspected. These librators have now been confirmed, and a possible 4:7 librator and possible second 3:5 librator have also been found. The known and suspected multiple-opposition librators are listed in Table 1. Here it is important to note that the orbital semimajor axes a (in AU), eccentricities e and inclinations i (in degrees with respect to the 2000.0 ecliptic) are mean values that eliminate the large 12-year and 30-year periodicities arising from the indirect perturbations by Jupiter and Satum on sun-centered orbits. The numbers in parentheses are the semimajor axes (in AU) corresponding to the resonances. Following the absolute magnitude H, the entries “Nep.” and “Ura.” show the minimum distances (in AU) from Neptune and Uranus (the latter being of course quite small for the most eccentric 2:3 Neptune librators) within several millennia of the present time.

Astronomers have been consciously making positional observations of comets since the sixteenth century, and rough information on bright comets is available from social records collected in the Far East, the Middle East and Europe over the previous two millennia. Attempts at representing the observations with orbits also date back to the sixteenth century, well before the earliest computations were made on the basis of gravitational theory. Improvement in the accuracy of cometary astrometric data was slow to develop following the invention of the telescope and, a few decades later, the micrometer, for this had to await the availability of Flamsteed’s star catalogue and the understanding brought about by Bradley’s discovery of aberration and nutation. In spite of important contributions by some of the most celebrated scientists of the eighteenth century, orbit computation remained largely a process of trial and error until the discovery of the first asteroids and the rise of Gauss and his followers. By the 1880s the availability of a dense star catalogue like the AGK1 was allowing micrometric observations of comets and asteroids often to achieve an accuracy of 2 to 3 arcsec, and the subsequent introduction of photographic astrometry brought convenience but relatively little additional improvement in accuracy. The use nowadays of charge-coupled devices clearly has the potential for a further increase in accuracy, even for diffuse objects like comets, but for the moment the accuracy tends generally to be limited by the inadequacy of the available star catalogues. Modern orbit determination routinely includes the use of sophisticated techniques to identify isolated observations of the same asteroid at different oppositions and in the case of a comet the examination of the nongravitational effects that can strongly influence the object’s motion.

Of all the sections of the International Astronomical Union the Central Bureau for Astronomical Telegrams is undoubtedly the one that most concerns amateur astronomers. Just about anybody in the world with at least some familiarity with the sky has the potential to discover (or to think he or she has discovered) a comet or nova. If the object is real and sufficiently bright, it is very probably already known. Somebody has to be the first discoverer of every comet or nova, however, and soon after the IAU was established in 1919 it set up the Central Bureau to receive and to disseminate to the astronomical community news of such discoveries. Discoveries of supernovae in other galaxies, natural satellites of the planets, erupting x-ray sources and transient features on the planets are also dealt with by the Central Bureau, which since 1965 has operated at the Smithsonian Astrophysical Observatory in Cambridge, Massachusetts. The Central Bureau handles unusual minor planets in the vicinity of the earth, although the thousand or more ordinary minor planets routinely discovered each year (and with which amateurs are being increasingly involved) are more appropriately the province of the Minor Planet Center, set up by the IAU in 1947 and since 1978 also operated at the Smithsonian Astrophysical Observatory. About one-quarter of the subscribers to the various services of the Central Bureau and/or the Minor Planet Center are individual amateur astronomers or organizations of amateurs.