Using accelerator mass spectrometry the cosmogenic isotopes 26A1 (half-life 716,000 years) and 10Be (1.5 × 106 years) have been measured in deep sea magnetic spherules. Because 26A1 can be abundantly produced by relatively low energy solar flare particles, while 10Be is mainly produced by higher energy galactic cosmic rays, the ratio 26Al/10Be of a body irradiated in space increases as the size of the body decreases. Our measured ratios of 26Al/10Be in the spherules are much larger than found in meteorites, and indicate irradiation in interplanetary space of a parent body of ≲ 1 cm diameter. Since most bodies of this size entering the atmosphere are associated with cometary orbits, our results strongly suggest that these spherules represent cometary debris. Our results also suggest an irradiation time in space of the order of 106 years for the parent bodies.

In order to study the inhomogeneity of the solar materials at the initial state, the enrichment factors and isotopic anomalies of refractory elements in deep sea spherules relative to the average solar abundance were examined using instrumental neutron activation analysis. Fairly high enrichment factors and isotopic anomalies of refractory elements were observed in several spherules, however, after the ablation process of the spherules during the atmospheric heatings they were not inconsistent with those of normal values in the solar system.

The cosmic ray exposure ages of deep sea metalic lie spherules were determined by various methods; low level countings (Ni-59), neutron activation analysis (Mn-53), high energy accelerator mass spectrometry (Be-10, Al-26) and mass spectrometry (K isotopes). The exposure ages of 0.3 - 50 Ma were obtained. According to Poynting-Robertson effect, the starting points (supplying sources) are located at inner region of the orbit of Saturn.

In 1980 (Phil. Trans. Roy. Soc. 297, 495) and in 1983 (Geophys. Jour. Roy. Astr. Soc. 75, 473) it was proposed that cosmic spherules are formed as splash ejecta in asteroidal collisions. The Poynting-Robertson effect size-sorts the spherules as they spiral to Earth in circular orbits. The time taken in My is given by

Δt = 3.5 × 10−7 Dδ (a2 − 1)

where a (in AU) is the collision distance from the Sun, D (in um) is the diameter of the spherules and δ (in kg/m−3) its density. In the 1983 paper, we tested the hypothesis by plotting the size of all the iron spherules (≥ 43 μm diam.) against time for two dated N. Pacific cores. Sloping lines, giving a ~ 2.1 AU, could be discerned; but their existence could be disputed - see figure 6.

In current work, all the spherules from core V21-65 have been cracked open to find δ. Out of 220 spherules, 65 have rusted metal globules and these (Dδ) points give a confused plot, because of inaccurate δ-values. However, 66 spherules have their metal globules well preserved. Since globule diameter and %Ni can be accurately measured, δ can be calculated. These (Dδ) points show two sloping lines with some clarity, giving a ~ 3.4 AU; also, there are vague lines, giving a-values well within the main asteroid belt.

To establish the hypothesis, wide cores are needed, giving an abundance of undamaged spherules. To obtain accurate a-values, the Robertson formula requires correction because of the spherule’s “hummocky” oxide surface. Also, any waviness in the sloping lines could be a measure of a variable solar constant.

A new kind of iron spherule was found because of the cracking; 13 enclose opaque beads of true glass (rich in Fe, Ni and Si, no Mg) instead of metal globules. Crushed bits are deep ruby-red and nonmagnetic.

Occurrence of anomalously high 3He/4He ratio (> 5 × 10−5) is rather common in the Pacific deep sea sediment. The 3He/4He ratio correlates well with the 3He content, whereas the 3He content shows approximate inverse relation with the sedimentation rate. Input of stratospheric dust of about 1 ppm or less which corresponds to about 2000 ton/y fallout rate can explain the above observation.

Periodicity in rainfall singularities in the U.S.A. corresponds to the periods of two comets whose orbits are sufficiently close to Earth’s orbit. These effects are connected with the position of a stratospheric jet stream over the territory of the U.S.A. This investigation indicates that some processes, so far not properly understood, could be responsible for the influence of cometary dust on the triggering of atmospheric precipitation.

A survey on different techniques of scattering measurements is given. Typical results are presented. Efficiency and limits of theoretical methods available are shortly summarized. Special emphasis is given to the demands on future laboratory experiments needed for the interpretation of polarization and colour effects produced by interplanetary and cometary dust.

Partial but significant localization along the line of sight (l.o.s.) of the contributions to the integrated zodiacal brightness can be achieved, without recourse to rash physical assumptions, if we focus on the two intersections between the l.o.s. and the terrestrial orbit. Then, there exists on the l.o.s. two other points or “nodes”, the contributions of which can be retrieved with outstandingly low uncertainty. The photometric results at these nodes (heliocentric change of scattering efficiency, backscattering phase function etc.) are highly reminiscent of previously ascertained features, and they encourage extensions to the polarimetric, the spectrometric and the radiometric cases. The salient results are, respectively: a positive radial gradient of local polarization degree; orbital velocities in excess over the keplerian ones, at least outside the earth’s orbit; the derivation of local temperatures from IRAS data.

A linear combination of 3 Henyey-Greenstein phase functions is substituted for the mean volume scattering phase function in the zodiacal light brightness integral. Results of the integral are then compared with the observed brightness to form residuals. Minimization of the residuals provides us with the best combination of Henyey-Greenstein functions for the scattering phase function of zodiacal dust particles.

At Bochum there exist three experimental setups for measurements of the scattering properties of dust particles. The microwave analog experiment is the best choice for systematic studies of particles in the size range between 0.5 and 10 times the wavelength (correspondig to about 0.25 to 5 μm in the optical region). The multicolour laser experiment providing electrodynamic suspension of single dust particles is optimized for studies of particles in the size range between 20 and 150 μm. Another laser experiment is designed for rapid analysis of particle mixtures in view of in-situ applications. The measuring principles of all instruments are shortly summarized.

The investigations of light scattering by larger meteoritic and terrestrial single grains (size range 20 μm to 120 μm ) demonstrate that the scattering properties of irregularly shaped dark opaque particles with very rough surfaces resemble the characteristic features of the empirical scattering function as derived from measurements of the zodiacal light. Purely transparent or translucent irregularly shaped particles show a quite different scattering behaviour. Furthermore irregular and multicomponent fluffy particles in the size range of a few microns were modelled by microwave analog measurements in order to explain positive and negative polarization of the light scattered by cometary dust grains.

Data obtained through microwave analog measurements are used to compare optical polarization characteristics of silicate particles ranging in shape from spheroids and cylinders to chains of spheres. It is confirmed that the dependence of the degree of polarization on scattering angle is a powerful indicator of particle shape. The reversal and steep gradient in the degree of polarization found by Weinberg and Beeson (1976a,b) in the dust tail of comet Ikeya-Seki (1965 VIII) is suggestive of laboratory measurements corresponding to 1.6 μm long, 0.4 μm in diameter silicate cylinders.

An experimental device, of the nephelometer type, to study the scattering properties of dust particles is presented. A fluidized bed generator produces a continuously flowing aerosol which is illuminated by either a He-Ne laser or a Xenon are lamp with interference filters. The size of the dust particles ranges between 1 and 30 μm. The scattering properties of dust particles are measured in the two directions of polarization. The first results are presented.

The influence of surface roughness on scattering properties of light is examined in terms of our previous mathematical method (Mukai et al. 1982). We found that albedo for single reflected light increases with an increase of surface roughness. In addition, a higher order of reflection light becomes effective for stronger rough particles.

Using our model of light scattering by large rough grains, the compatibility of the observed properties of the zodiacal light with models of the spatial density of interplanetary grains is investigated. The agreement is not yet satisfactory and probably calls for further revision of the density distribution function. Our previous conclusion that submicronic grains gives a non-negligible contribution (Lamy and Perrin, 1980) is confirmed.

Recent work on the light scattering by large rough particles has led us to propose a model based on the high-energy approximation, the laws of geometrical optics and a mathematical description of the properties of the particle roughness. The influence of the various parameters of the model including those characterizing the roughness on the total intensity and the polarization is presented.

We calculated the scattering cross section of an ensemble of large, convex, randomly oriented particles with a slight surface roughness. If the roughness structure is described by an exponential correlation function, the degree and angular dependence of the zodiacal light reddening are well reproduced by our model.

Several models of three dimensional distributions of the interplanetary dust number densities are compared with observational values. It is shown that a comparatively satisfying fit can be achieved by distributions similar to the “Sombrero-Model” of Dumont and that multilobe models as recently proposed by Buitrago et al. can be rejected due to discrepancies with rocket photometry of the inner zodiacal light.

The equilibrium temperatures of spherical grains of pure H2O, CO2 and NH3 ice in the solar system are computed at heliocentric distances ranging from 1 AU out to (> 1500 AU) where solar illumination becomes negligible compared to galactic and extra-galactic light; the grain size range is from submicron to tens of meter in diameter. These results are based on recently published optical constants and on the use of the “complex angular momentum” (CAM) theory for computing the interaction of the grains with light.

We deduce the optical efficiency Q (λ)/ a of the circumstellar dust material over the range 8-30 μm from twelve M and G giants and supergiants and that of the dust present in the general ISM and molecular clouds from thirteen protostars. We then discuss the differences between these two profiles in the light of the condensation theory.