Comet P/Halley was observed polarimetrically for seven nights in IHW and other continuum filters, during the pre and post perihelion passages. The polarimetric observations have been combined with the observations taken by other investigators, to get a complete picture of phase angle and wavelength dependence of polarization of comet P/Halley. Assuming Mie type scattering by cometary grains, the observed polarization data were fitted for a set of complex refractive indices which are (1.387, .032), (1.375, .040) and (1.374, .052) at .365, .484 and .684μm respectively.

Approximately 68,000 orbits of meteoroids, ranging from sizes of 10 cm and more down to microgram masses, are now available through the IAU Meteor Data Center. These orbits were measured in surveys based in the U.S.S.R., the U.S.A., Canada, Somalia, and Australia, using photographic, radar and television techniques; the data represent our best knowledge of the orbital distributions of smaller solid bodies in the solar system. It is found that quite different distributions result in different mass regimes, with implications for the origin and evolution of these particles: for example the larger bodies, observed as fireballs, are associated with meteorites in coming from the region of the asteroid belt with low-inclination orbits, whereas the smaller meteoroids have more comet-like orbits. There is also evidence for several meteoroid streams associated with specific Apollo asteroids. The data may additionally be viewed as a suitable source function in investigations of the production of interplanetary dust from the fragmentation of larger meteoroids in mutual collisions. However, inspection of the data raises many questions: for instance there seem to be many meteoroids on small retrograde paths, but no possible parent objects are known to exist on such orbits.

A list of 325 two-station photographic meteor orbits obtained with 35 mm cameras has recently been published by Japanese amateur groups. The present study analyzes the data and concludes that the orbits are of high quality and very useful for scientific purposes.

The temperature and the radius variation of micrometeoroids in the thermosphere and the mesosphere are calculated theoretically. If the radius and the initial velocity are 100 μm and 30 km/sec respectively, the evaporation height and the velocity coincide almost exactly with those of the Capricornids and the Virginids from the meteor stream observation.

Moreover, it is shown that the not evaporated debris till the end of the sublimation may become spherules in the bottom of deep sea; and that fluffy micrometeoroids (10μ size) floating in the stratosphere are also consistent with our calculation.

The recondensation and the coagulation of the evaporated gas molecules from the meteoroid are also calculated, and it is shown that these secondary particles are very small and few.

This work was done to estimate meteoroid fluxes of steady meteor streams at places far away from the sun, for example, beyond Martian orbit. For the estimation, a Normal Distribution Model is introduced. This model assumes that the flow of meteoroids is steady and the meteoroids are distributed in the form of a normal distribution around the orbit of their parent comet. Keplerian motion of each meteoroid is also assumed. Some parameters, necessary for determining a practical model, can be obtained through observations. The model will give the overall structure of meteor streams and their fluxes can be calculated for any points on the orbits of their parent comets. Calculations show that fluxes of streams sharply decrease as the solar distance increases and that meteoroids scatter chiefly along the orbital planes of the parent comets. The model seems to be useful to deduce rough structure of meteor streams.

The purpose of the IAU Meteor Data Center in Lund is to archive, document and disseminate information on meteoroid orbits. At present some 6 000 photographic double-station orbits and 60 000 radio determined orbits are archived.

The probable association of Comet IRAS-Araki-Alcock with the η Lyrid meteor stream is suggested, and the possible relation of the radio meteor shower on 1983 May 10 is also discussed.

The radio observations of meteor echoes using FM broadcasting were carried out from January, 1981 to June, 1985. The annual variation of meteor rates in the 5 years was obtained from the observations made from 25h through 29h in local time (16h-20h UT).

Some features in this annual variation can be explained by the occurrence of the major meteor showers. After the effects of these major showers are removed there remains a significant annual variation which shows higher rates in the winter half of the year (October to March). This seems to be caused by the annual variation of non-shower meteors radiating from the apex region.

Critical examination of the orbital parameters of particles ejected from comet Halley rejects the low age hypotheses for meteor showers associ- ated with the comet. The diffusion of the orbits of large particles is too slow for explaining the observed structural features of the stream. The mass-loss process as derived from space observations compared with the mass of the stream of particles deduced from flux data lead to comet lifetimes of the order of 105 years.

The formation and evolution of the Taurid Complex of interplanetary objects is modelled on the basis of the parent being a giant comet which entered the inner solar system some time in the past 10,000-20,000 years. The orbital element distributions for the presently-observed meteor showers are discussed in terms of how these can constrain any model for the origin of the overall complex. As a baseline model we present results from the numerical integrations of fictitious meteoroids released from a comet over ten millenia, this comet having initial elements similar to those derived from a backwards integration of P/Encke. Large relative velocities at perihelion, above those feasible in conventional ejection scenarios, are necessary; we ascribe these to jetting of organics and other volatiles soon after release. Such a model gives a good first-order fit to the observed orbits, although additional processes (cometary splitting or asteroidal collisions) appear also to be necessary to explain the Taurids.

Mass distribution of the interplanetary dust is reexamined taking into account bulk density distribution of the dust and larger particles. It can be shown that the mass index of particles depends on the evolutionary stage of the population and changes along the mass scale. The flattening of the mass distribution at the higher mass range may explain the problem of the equilibrium between the source and sink of the interplanetary dust.

Founded in 1988, the International Meteor Organization (IMO) is an international scientific non-profit association with members all over the world. The IMO was created in response to an ever growing need for international cooperation of amateur work. As such, the main objectives of the IMO are to encourage, support and coordinate meteor observing, to improve the quality of amateur observations, to make global analyses of observations received world-wide, to develop contacts between amateurs and professionals, and to disseminate the observations and results obtained to other amateurs and to the professional community.

The life cycles of grains in circumplanetary space are governed by various physical processes that alter sizes and modify orbits. Lifetimes are quite short, perhaps 102-104 years for typical circumplanetary grains of 1 micron radius. Thus particles must be continually supplied to the circumplanetary complex, probably by the grinding down of larger parent bodies in collisions. Dust is eroded gradually through sublimation and through sputtering by the magnetospheric plasma but also is catastrophically destroyed through hypervelocity impacts with interplanetary micrometeoroids. Orbits evolve through momentum transfer (light drag, plasma or Coulomb drag, and atmospheric drag), and through resonant gravitational and electromagnetic forces. Plasma drag is generally the most effective evolution mechanism, with the possible exceptions of exospheric drag at Uranus and of electromagnetic schemes for some conditions. Since grains become charged (with typical electric potentials of a few volts), they undergo associated orbital perturbations: variable electromagnetic forces can cause the systematic drain of energy (orbital collapse) or, at specific (resonant) orbital locations can force large orbital inclinations/eccentricities. Solar radiation induces a periodic orbital eccentricity that can reach substantial values for 1 micron particles distant from the giant planets.

Each of the outer gas giants Jupiter, Saturn, Uranus and Neptune is now known to be encircled by a system of rings. Some of these, such as the A, B, and C rings of Saturn and the nine narrow Uranian rings, are rather optically thick and are composed primarily of large bodies (1 cm to 10 m). However, every other system has been found to contain a large population of micron-sized dust. Such rings reveal the effects of a variety of physical processes that are also acting on interplanetary and interstellar grains. When such rings are examined as members of a general class, recurring patterns begin to emerge.

The micron-sized dust forming the radial spoke-like features in Saturn’s rings are studied using radiative transfer analysis. Theories for their likely origin and evolution are discussed in light of these results, and future work is outlined.

The results on mass, velocity, shape, and rotation of the fragments produced in the disruption experiments by impact are surveyed. Some future works are also suggested.

Particles of radii 0.2 to 3 μm and of different materials were suspended in an electrodynamic quadrupole inside a vacuum chamber and exposed to beams of electrons and ions of energies up to 20 keV and 5 keV, respectively, with the aim to simulate electric charging of cosmic dust particles. It was found that the equilibrium surface electrostatic potential of glass particles of radii 0.2 to 2 μ charged by electrons of energies 1 to 20 keV is always positive. This can be explained by secondary electron emission at lower energies of electrons and by penetration of electrons through particles with subsequent secondary electron emission mainly from the exit side at higher energies. In case of charging by ions electrostatic potential of particles is generally much lower than expected values and interpretation of results of measurement is more complicated. The most promising way to eliminate instrumental influences disturbing processes of charging seems to be a construction of a smaller suspension system in which these influences would be negligible. Parameters of such a suspension system were derived from results of measurements.

An enhancement of the electrostatic stress forces due to the charge concentration on a position with small radius of curvature on the surface of irregularly shaped particle causes the fragmentation of fluffy particle more than expected for a spherical particle. This mechanism may act to produce “dust clusters” as detected in comet P/Halley by Simpson et al. (1987) and also “dust swarms” near the Earth as reported in Fechtig(1982).

Collisions of icy objects play a major role in the outer solar system. The purpose of this investigation is the experimental study of plasma production by dust impacts on icy surfaces. Impact speeds ranged from 3 to 60 km/s. It was found that the dominant ion species which were released are both positive and negative water clusters. The impact charge yield from icy surfaces is approximately a factor 100 below that from previously studied gold surfaces.

One of the key outcomes of collisional disruptions to the dust system is the velocity distribution of fragments. A series of laboratory impact experiments were carried out to obtain the mass-velocity and the position-velocity relation of the fragments by taking movie films, and films for tow impacts were completely analyzed.