Information on the dynamics of interplanetary dust is obtained by observations of radio-meteors, zodiacal light, thermal infrared emission, and by measurements with in-situ detectors on board Earth satellites and deep spaceprobes. These methods are sensitive to different meteoroid sizes (mm- to sub-micron sized) and refer to different regions of space. Bigger particles (> 10-9 g) move on bound Keplerian orbits and are dynamically dominated by solar gravity, while the trajectories of particles smaller than 10-10 g are strongly influenced by radiation pressure and electromagnetic interactions. Modelling interplanetary dust is done by dividing the whole meteoritic complex into dynamically distinct populations. Divine's (1993) model identifies five dynamically different populations of interplanetary meteoroids: bigger particles are described by the “core”, and “asteroidal”-populations, intermediate sizes by the “halo”-population, and small particles are included in the “eccentric” and the “inclined”-populations. The intermediate and the small particle populations, in particular, have to be redefined for several reasons: new data are available which require the consideration of hyperbolic orbits and the inclusion of radiation pressure and electromagnetic forces. New small particle populations are interstellar dust and beta-meteoroids.

Divine (1993) developed a mathematical model to use measurements of interplanetary dust to determine the orbital distributions of particles in interplanetary space. The power of the model is that it uses the fact that the dust particles are in Keplerian orbits to correct for the observation biases based on spatial density and velocity efifects of the orbits. In order to do this, he creates families of dust orbits; within each of which the particles have mathematically separable distributions of mass, periapsis, eccentricity, and inclination. He then uses a trial-and-error method to vary these distributions until an adequate fit is made to the data. Each of his distributions is loosely based on populations of interplanetary dust that are believed to be present in the Solar System.

Results of Ulysses impact measurements are compared to Zodiacal cloud models. We discuss the influence of radiation pressure forces on particles of different size and composition and show its relevance for the understanding of impact measurements, and give an upper estimate for the dust density in an IRAS dust band.

Six streams of dust were unexpectedly detected by the Ulysses dust detector while this spacecraft was approximately within one AU distance from Jupiter (Grün et al., 1993). Stream durations ranged from hours to days for individual streams. It was clear that the dust in these streams (or bursts), from their directionality of approach to the spacecraft and from the nearness of stream occurrences to Jupiter, emanated from the Jovian system.

Following the original report, Baguhl et al. (1994) later relaxed the criteria for differentiating true dust impacts from “noise pulses” and found almost triple the number of dust impacts in the six streams already found. They also found 5 more streams that, except for one stream, clearly emanated from the Jovian system. The criteria were relaxed in such a way as to not introduce “noise events” into the data.

The Cosmic Dust experiment on the Hiten spacecraft detected more than 500 events likely to be associated with particle impacts during its three years life in space. An excess of approximately 40% was observed in the direction of 220° ecliptic longitude. This direction corresponds well with the direction of the reported interstellar Helium and interstellar dust seen by other experimenters. In absolute number this is about 20 particles. Since this data was taken during three full years and thus most other effects should be averaged out we believe that these particles are of interstellar origin.

Collisions of asteroids and among Zodiacal cloud particles produce large amounts of submicron-sized debris, much of which is immediately ejected from our solar system by electromagnetic forces. We investigate the trajectories of tiny grains started on circular uninclined orbits within the Zodiacal cloud and find that they reach high ecliptic latitudes during the current configuration of the solar magnetic.field, perhaps accounting for particles detected by the Ulysses spacecraft at latitudes up to 80°. When the solar magnetic field is reversed, particles are more strongly confined to the ecliptic plane and escape the solar system less readily. Both fluxes and spatial densities of sub-micron sized Zodiacal dust particles vary with time through the dependence of orbital dynamics on the 22-year solar cycle.

The local cloud in which the Sun is embedded participates in a general flow from the direction of the Sco-Cen association (Weaver, 1979) while the Sun is moving in the direction of Hercules. The relative motion is well determined by the neutral gas flow (Cox and Reynolds, 1987). A prominent cone of gravitationally focused neutral helium indicates the downwind direction to within ±3°. The average flow speed outside the solar system, 26 km/s, is determined to within ±1 km/s. Measurements from the Ulysses spacecraft (Witte et al., 1993) confirmed this flow. Since interstellar matter contains dust as well as gas, efforts have been made to detect the dust flow through the solar system. However, until recently these efforts have been unsuccessful and modeling of the flow has been controversial.

Trapping of dust particles into external resonances with the inner planets is a quite relevant phenomenon, which induces the formation of rings of dust around the planets' orbits, there being observational evidence of the Earth's resonant ring (Dermott et al., 1994). On the other hand, notwithstanding it is a less probable event, capture into internal resonance (diverging orbits) is predicted in numerical integrations of dust particles' orbits subject to Poynting-Robertson drag with one or two disturbing planets. Average theories, which give a good explanation for resonance trapping when the orbits are converging, do not allow capture for diverging orbits. Close approaches with the perturbing planet disallow the application of average theories, and numerical examples show that resonance trapping for internal resonances must have a chaotic origin. As expected from analytical theories, for the case of one disturbing planet, the particle's eccentricity decreases continually after capture and resonance is eventually broken. When two disturbing planets are present, however, there is not necessarily a decrease of the eccentricity, but it may increase, decrease or oscillate, although escape from resonance always occurs anyway.

We introduce the continuity equation written in the coordinate space of the orbital elements (e.g. large semi-axis a vs. eccentricity e, etc.) to explore the density evolution of the zodiacal cloud. Emphasis is on those terms of the continuity equation which describe ‘jumps’ of particles in the (a, e)-space due to gravitational scattering of the interplanetary dust particles by planets, which represents one of the leading factors in the dynamical evolution of the zodiacal cloud. In the remainder (div-terms of the continuity equation), one can incorporate the known analytical expressions for the rates of gradual change of orbital elements due to the Poynting-Robertson and solar wind drags (Liou et al. 1995).

We have estimated the flux of lunar ejecta near the Earth, e.g., the cumulative flux of ejecta larger than 10-13g is 10-10particles cm-2s-1. In addition, our numerical simulations for the orbital evolution of lunar ejecta lead to the orbital characterization of these ejecta. Since our calculations suggest that the incident direction of lunar ejecta onto the Earth is nearly isotropic, it is expected that the dynamical properties of lunar ejecta make it possible to distinguish them from other IDPs.

Interaction of a meteoroid penetrating the atmosphere can be described through its motion, ablation, luminosity, ionization and the geometry of its trajectory. A theoretical description may be based on the so called “single body theory”, generalized to allow for discrete fragmentation. Such a concept is fully able to simulate the motion and ablation (mass loss) of meteoroids from millimeter to meter sizes recorded through photographic techniques (the best precision of such observations is better than ±10 m in observed heights). Observed distances and heights as a function of time can be fit to this model with the intrinsic precision of the geometrical data. The majority of meteoroids follow the “single-body theory” closely: large values of the ablation coefficients derived from observations favor continuous fragmentation under very low dynamical pressures as the main process of ablation. The rest, some 20 to 30%, can be described by one or more discrete fragmentation points in addition to continuous fragmentation. Dynamic pressures at these grossfragmentation points are also very low, if compared with the strength of stony meteorites.

On the other hand, luminosity and ionization are not as well understood. Existing detailed spectral records show mostly radiation in form of emission lines of ablated meteoroid material with excitation temperatures in the range of 3000 to 5000 K. Additional theoretical modeling is called for.

Photographically documented meteorite falls can be used for computation of luminous efficiencies, because the terminal mass and bulk density are known in these cases. Recently, photographs of the Lost City meteorite fall were remeasured with special attention to visible trails of fragments. The new analysis revealed two main discrete fragmentation points that are in perfect agreement with the geometrically resolved trails based on the dynamics. Moreover, Adolfsson (1996) found an artificial periodic signal originating from the switching shutter and after removing this signal, he was able to find an initial rotation period of 3.3±0.3 s and also the rotation phase of the Lost City meteoroid. A solution for the motion, ablation and rotation of the Lost City meteoroid is now completely self-consistent throughout the whole photographed trajectory and yields an initial mass of m = 163 ± 5 kg. The luminous efficiency was found to be 6.1% at v = 13 km/s (for 4500 K), this is ∼ 10x larger than the values determined from artificial meteors, i.e., from masses of 1 g fired downward from high-altitude rockets by shaped-charge.

Some 3 x 105 radar meteoroid orbits have been secured to date by the AMOR, project since its inception in 1990. For many types of study it is important to realize a high angular resolution; for example to probe more incisively meteoroid stream orbital structure in order better to determine the rôle of the various processes controlling stream dynamics. The orbital precision of AMOR has been enhanced by developing a new dual spacing interferometer using single channel phase detection. In addition, a Doppler-sensing facility has been incorporated to record simultaneously data concerning middle atmospheric dynamics allowing better interpretation of the individual echo signals.

The results of testing the classical method of velocity determination based on the positions of the extrema of Fresnel diffraction patterns (FDP) in radio echo amplitude, is presented. This technique is compared to the method of nonlinear least squares fitting (NLSF) of the theoretical patterns to the observed those. It is shown that while the classical method can fail in yielding correct values for the velocity of radar meteors, the NLSF method always yields good results.

We have implemented a 54 MHz radar located near Adelaide, South Australia, for novel forms of meteor observation. Here we describe a radically new form of meteor speed determination: we measure the rate of phase change for head echoes obtained from meteors propagating down the beam towards the radar. These not only provide speeds of unprecedented precision, but also deliver accurate deceleration measurements, these being of importance in understanding the meteoroid ablation process and exploring the physical parameters of such bodies.

The occurrence of fragmenting particles was investigated from radar observations of the Perseids at Ondřejov Observatory. Diurnal patterns of fragmenting meteoroids are presented. Their minimum occurrence coincides with the culmination of the Perseid radiant while the maximum appears at the time of sunset at meteor heights. Solar longitude of the main contribution of fragmenting meteoroids at L⊙ = 138°86±0°04 (equinox 1950.0) fits with the peak activity of the new filament in the stream. This supports the concept of the low age of the filament. The maximum proportion of fragmenting particles occurred in 1991.