Cosmic Dust Grains Research Articles

On the Electrical Effects of the Presence of Fluff on the Surface of Cosmic Dust Grains

AbstractWe 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.

Light scattering by anisotropic particles

The Stokes parameters of radiation scattered by anisotropic particles (cosmic dust grains or molecules) are calculated. The effective mechanisms of transformation of the linear polarization into the circular one by free-oriented anisotropic particles are proposed. The optical activity of the irregular-shaped particles is shown to be rather large even though they consist of isotropic inactive material.

Ориентация космических пылинок

The orientation of nonspherical cosmic dust grains is found in the anisotropic corpuscular or radiation fluxes and in the presence of the magnetic field; the grains being approximated by the axially-symmetrical ellipsoids. The comparatively small twisting is shown to cause the difference in scattering of the right and left circular-polarized light and the increasing of the angular momentum. If the period of the angular momentum precession caused by the magnetic field is less than the time of the orientation by the corpuscular or radiation fluxes, then the distribution of the grains' axes gets the symmetry relative to the field direction. It is shown that such orientation realized in our Galaxy allows us to explain easily the interstellar linear polarization observed. The mechanisms of the grains' orientation near the infrared source Becklin-Neugebauer, in the B 96 cloud near RY Tau and in the comet Bennett are discussed.

Orientation of cosmic dust grains

Orientation of nonspherical cosmic dust grains is found in anisotropic corpuscular or radiative fluxes and in the presence of the magnetic field; cosmic grains being approximated by axially symmetric ellipsoids. A comparatively small twisting of grains is shown to cause differences in scattering right-hand and left-hand circularly polarized photons and growth of the angular momentum. If the period of the grain's angular momentum precession induced by the magnetic field is shorter than the time of orientation by corpuscular or radiative flux, distribution of grains' axes becomes symmetric relative to the magnetic lines. This orientation mechanism easily explains interstellar linear polarization observed in our Galaxy. The mechanisms of grains' orientation near the Becklin-Neugebauer infrared source, in the B 96 reflected cloud near RY Tau and in cometary heads are proposed.

Ion implantation effects in space: X. surface scattering

Cosmic dust grains present in various types of astrophysical sites have been exposed to high integrated doses of low energy ions ( E ≈ 1 keV/amu). which produce ultra-thin amorphous coatings of radiation damaged material loaded with “saturation” concentrations of implanted species such as C, N, O and H nuclei. These ion implantation effects can be used to tackle a wide variety of problems concerning the thermal properties of the ancient solar wind and the past activity of the Sun, the mass spectrum of the ancient meteorite flux, the “sticking” processes responsible for the formation of cm-sized “gravels” in the early solar nebulae, the synthesis of small molecules in interstellar clouds, and the gradual “ageing” of cosmic dust grains in galaxies. On the other hand new methods have been developed to get information from the individual radiation damaged islands registered in silicate targets exposed to very low integrated doses of low energy ions both in space and in Earth's Laboratories.

Ion implantation effects in “cosmic” dust grains

Cosmic dust grains, whatever their origin may be, have probably suffered a complex sequence of events including exposure to high doses of low-energy nuclear particles and cycles of turbulent motions. High-voltage electron microscope observations of micron-sized grains either naturally exposed to space environmental parameters on the lunar surface or artificially subjected to space simulated conditions strongly suggest that such events could drastically modify the mineralogical composition of the grains and considerably ease their aggregation during collisions at low speeds. Furthermore, combined mass spectrometer and ionic analyzer studies show that small carbon compounds can be both synthesized during the implantation of a mixture of low-energy D, C, N ions in various solids and released in space by ion sputtering. The present results have implications concerning the origin of small molecules in interstellar or circumstellar clouds, the “aging” of cosmic dust grains in space, and the “sticking” process in the solar nebula.