Laboratory infrared absorption spectra of interplanetary dust particles show that most fall into one of three spectral groups (1) designated as “pyroxenes”, “olivines”, and “hydrated silicates”.

Comparisons with 10 μm emission data from Comet Kohoutek (2) show that no single spectral type matches the cometary data. However, a reasonable match is obtained by coadding equal amounts of pyroxene and hydrated silicate type spectra.

The possibility that the 10 μm feature seen in some comets is due to a combination of these two components can be tested in two ways. First, the pyroxene type spectra show detailed features of variable position and strength within their 10 μm bands. Based on the laboratory data we estimate that comet spectra taken at a resolution of λ/Δλ ~ 200 would be sufficient to find these features, if present. The magnitude of these features is expected to be ≤ 0.1 of the maximum strength of the 10 μm band.

Second, the hydrated silicate particles usually have bands at 3.0, 6.2, and 6.9 µm. The first two bands are probably linked to the presence of water while the 6.9 μm band is probably due to carbonates. The 3.0 μm feature is broad and might be hard to separate from thermal background. However, spectra taken at resolutions of λ/Δλ ~ 50 could see the 6.2 and 6.9 μm bands. The strengths of these bands (which are also seen in the spectra of CM meteorites) vary (one particle has a carbonate band that is actually stronger than its corresponding 10 μm silicate band), but are typically ~0.1 the depth of the silicate features. A second, narrow carbonate band at 11.4 μm can also sometimes be seen in particle spectra but its strength is less than that of the 6.9 μm band. This the search for the 6.2 and 6.9 μm bands in astronomical objects, while not requiring high resolutions, would require good S/N.

A number of experimental releases into low earth orbit of small, but detectable, quantities of very fine particulates are planned for the next several years. The principal materials are chemically and physically similar to those generally assumed to be the major constituents of interplanetary and circumstellar dusts (silicates, silicon carbide, graphitic materials). Later releases will include multi-phase releases of non-volatile particulates and volatile ices, simulating cometary material. Both ground-based and Space-Shuttle-based observations will be made in the visible and infra-red to study particle-plasma interactions, cometary physics and cloud dynamics in orbit.

Since opportunities for observing the behavior of such well-characterized materials in space are likely to be rare, and the effective duration of significant concentrations will be very short, we wish to have early input from the scientific community so as to maximize the scientific return. We will be receptive to all suggestions including collaborations in making the observations.

The bimodal nature of distribution function f(γ) is confirmed by analysing the optical isophotal maps of comets Kohoutek 1973 XII and Bennett 1970 II. Extending the dynamic analysis to the infra-red data of two comets, Kohoutek 1973 XII and IRAS-Araki-Alcock 1983 d, we demonstrate that the secondary component f2(γ), which dominates in the range of large particles, plays a much more important role in emitting the thermal radiation (IR) than in the case of light scattering (optical). The relative weight of two components, measured by their height ratio, g2/g1, should be increased by a factor of about 20, in order to obtain a good fitting to the infra-red data.

The dynamic properties of the dust striae, observed in comets West 1976VI, and Mrkos 1957V, are reexamined in terms of the high speed emission model (HS model) proposed by Notni (1966). It is demonstrated that most striae can be well fitted to modified synchrones but this kind of fitting does not lead to a conclusive model; in most cases, the dynamic solution is not unique, and, furthermore, the derived high values of the ejection speed appear to be unrealistic, particularly for distant (or old) striae. The results suggest that the required initial velocity could be better interpreted as indicating the presence of nonradial acceleration.

There are three factors that inhibit detecting small comets relative to large comets: 1. They must pass closer to the Earth than large comets to be detected. 2. The resulting higher angular velocity for nearby comets means that, at comparable apparent magnitudes, there is less time available to discover a small comet relative to a large comet. 3. Small comets physically decay and vanish faster than do large comets. With these three factors, it can be shown that if the small comet input distribution gi (Rn) in varies as , where Rn is the nuclear radius of the comet, then the observed distribution will vary as

CCD sensors placed across the focal plane of large Schmidt telescopes have great potential for detecting and measuring the very low flux in space of meteoroids with diameters larger than 1 meter. With the Palomar “Big Schmidt”, a detection rate of 1.4 per hour is obtained for meteoroids between 0.6 and 200 meters in diameter. For the Baker-Nunn “Satellite Tracking Camera”, the corresponding rate is about 0.8 per hour. The key to obtaining such high detection rates derives from approximately setting the sensor integration time equal to the time it takes a meteoroid to cross a pixel field of view. This minimizes signal to noise problems and is accomplished, in practice, by multiple summing of short integration time data records to obtain data records of longer effective integration times.

A radar meteor orbit facility of novel design has been developed at the University of Canterbury. Synchronous digital noise averaging,impulse suppression and meteor echo recognition using a microprocessor system, along with high gain antennas, allow a limiting radar magnitude of about +13 to be achieved, making this the most sensitive meteor orbit radar to’ date. An exhaustive survey of faint sporadic meteors will be carried out, along with an investigation of the little-known Southern showers. Since the observatory is ideally located with respect to the Eta Aquarid radiant, a programme of observations during the Comet Halley perihelion epoch is planned.

Several, different forms of how neutral gases and dusty media can interact with a plasma have been discussed in the Literature. Common to all of these interactions is that they in principle lead to changes in both the composition and dynamical state of all interacting media. The most important scenarios in the heliosphere involving these kinds of interactions are described in this paper. Special emphasis is placed on the solar wind interaction with the zodiacal dust. In regard to the dust, this leads to severe complications with respect to its dynamics due to the plasma Poynting- Robertson effect and due to Lorentz scatterings. As for the plasma, this causes the appearance of dust-generated neutrals and secondary ions. An influence on the plasma dynamics, at least in the present solar system, can be neglected. The surface chemistry of the plasma-dust reactions is described in some detail here, and the densities and fluxes of exotic, dust-generated ions not originally belonging to the coronal solar wind are calculated. Observabilities of these neutrals and ions are investigated and it is discussed how physical, chemical, and dynamical parameters of the zodiacal dust cloud could be derived from these observations.

Along the lines of previous studies on the cometary dust-plasma interaction processes, we evaluate the electromagnetic effect of submicron dust in the coma and in the dust tail. The possible occurence of electrostatic disruption of charged dust in the ion tail is also discussed from theoretical and observational points of view. The relevance of these processes to the formation of striae in the dust tails of several comets is addressed and the conclusion is made that trajectory study of the submicron dust in the striae must take into account the action of the interplanetary electric field.

The charge of cosmic grains can be calculated if the optical constants, the photoelectric yields and the photoelectron energy distributions for a large range of energy of incident photons are known. Our measurements are made on several materials which are possible constituents of interstellar and interplanetary dusts. We present here our results for fused quartz, iron and carbon.

A continuing program aimed at improving the determination of the charge of interplanetary as well as cosmic grains is presented. Recent data have been combined to generate two high-resolution solar spectra corresponding to the maximum & minimum of activity. The energy distribution of photoelectrons emitted by quartz grains under solar irradiation is calculated using the new laboratory measurements of Quemerais et al. (this volume). Finally, the method of Lafon, Millet and Lamy (Astron. Astrophys., 95,295, 1981) is used to find the electrostatic potential of these grains.

We give a n analytical model describing the effects of “fluff” on the potential and the electric field on and close to a charged spherical body embedded in an astrophysical plasma. The consequences are investigated for dust grains biased at positive or negative potentials but large enough for electron or ion field emission to be active.

Secondary emission can play an important role in the charging of dust grains. This process is very sensitive to their size and to the physical properties of the solid. It is particulary important in the case of insulators in which an intense electric field is present at the surface and can accelerate the excited electrons.

As a consequence, the secondary emission yield δ does not depend on the energy of primaries and multiple solutions of the potential due to the usual non-monotonic form of δ versus the energy of primaries disappear.

The penetration of energetic particles from stellar winds, cosmic rays and fast moving gas clouds in interstellar dust grains induces a variety of physical and chemical changes. Detailed information on penetration ranges, number of secondary projectiles produced by knock-on and their energy distribution is obtained from computer simulation of collision cascades with the program MARLOWE. Model targets are polycrystalline H2O-ice, NH4Cl, and SiO2, projectiles are lo2 - lo4 eV H, He, and C. Depending on the energy and the projectile/ target mass ratio up to lo2 secondary projectiles are created per primary impact with energies ranging from a few to some lo3 eV. In composite grains, condensed gases and ice mixtures the energetic secondaries can undergo hot chemical reactions leading to a series of precursors for larger organic and biomolecules.

Energetic ions or atoms in space may undergo hot chemical reactions upon penetration into interplanetary or interstellar dust grains, ice layers, cometary matter, and surfaces of planetary moons. The mechanistic pathways can be different from those of classical ion molecule interactions, photolytical and radiolytical processes. The kinetic energy of the hot reactant facilitates endothermic reactions and those with high energy of activation, among them atom-molecule interactions. The conditions of hot cosmic chemistry are simulated in laboratory experiments in order to obtain insight into the nature of chemical products and the reaction mechanisms of their formation. This paper reviews the methods of ion implantation, nuclear recoil in situ, nuclear recoil implantation, secondary knock-on processes and computer simulation of collision cascades. Carbon and nitrogen impact in frozen H2O, NH3 and CH4 is shown to lead to the formation and radiolytic permutation of a series of organic molecules, among them e.g. formaldehyde, methanol, methylamine, cyanamide, formamidine and guanidine which may act as precursors for biomolecules.

The intensity of solar X-radiation scattered by a comet is calculated and compared to the proper X-radiation of the comet due to impacts of cometary and interplanetary dust particles. Detection of X-radiation of dusty comets at small heliocentric distances (R ≤ 1 a.u.) is found to be an indicator of high-temperature plasma generation as result of grain collisions.

Three attempts to explain the radial power law distribution n(r)~r−1.3 of interplanetary dust are reviewed, which include the influence of Poynting-Robertson effect, collisions and interplanetary magnetic fields. Electromagnetic forces are unlikely to affect appreciably the spatial distribution. The replenishment of the cloud of interplanetary dust by the disruption of larger meteoritic particles in catastrophic collisions appears to give the most natural explanation for the observed spatial distribution.

Tisserand’s definition of the “sphere of action” of a planet is based on the equality of tidal vs. gravitational acceleration ratios of the sun and planet. Öpik and others based their relation on equating the differential solar and planetary forces on a particle. Neither expression was formulated to describe the zone of influence surrounding a planet when considering the small, but significant, long-term perturbative effects of the planets on a particle’s orbital elements. For the purpose of determining these effects on interplanetary dust we derive a zone of influence based on equating the gravitational forces of the sun and planet.

Dynamical perturbations on ensembles of particles in heliocentric orbits of low eccentricity are integrated over time. The dust is perturbed by radiation pressure, Poynting-Robertson drag, their corpuscular counterparts, and by gravitation due to any number of planets. A dust cloud is represented by a set of centroids and orbital dispersions (about the centroids). Gravitational perturbations on the centroid are derived from a single matrix, valid for any planet, in the appropriate frame of reference. After transformation of the time derivatives to a common coordinate system, the perturbation rates are summed up and integrated. The time dependence of the planets’ orbital elements are evaluated inside the time integral.

Synthetic infrared pictures are used to illustrate changes in the shape of portions of an interplanetary dust-cloud. The dust particles, in circular heliocentric orbits, are perturbed by radiation and corpuscular forces combined with gravitational disturbances by the major planets. Dust in the inner solar system and close to the ecliptic or the orbital plane of Venus is brought to a more narrow range of ecliptic latitudes. A dust-band evolves near and inside the orbit of Venus. The cloud’s shape is less affected at high ecliptic latitudes.