ASTEROIDS AND COMETS:
POLARIZATION PROPERTIES
A
COMPARISON
OF
N.N. KISELEV1, V.K. ROSENBUSH2, E.V. PETROVA3, K. JOCKERS4
1 Astronomical Observatory of Kharkiv State University, Kharkiv, Ukraine
2 Main Astronomical Observatory of National Academy of Sciences, Kyiv, Ukraine
3 Space Research Institute, Moscow, Russia
4 Max-Planck-Institut füг Aeronomie, Katlenburg-Lindau, Germany
A detailed study of the linear polarization demonstrated by dark asteroids in
different spectral bands has been carried out on the basis of all the data
available, including our own measurements. The parameters of polarization
curves, such as min, Pmin, inv, h, Pmax, max, and their wavelength
dependence have been obtained.
In general, the synthetic phase curves of polarization for C-type asteroids and
cometary dust are very similar at small phase angles but they appreciably
differ at large phase angles. We analyze the peculiarities of the phase and
spectral dependence of polarization for comets and asteroids and discuss
them in the framework of existing mechanisms of light scattering.
In order to explain the negative branch of polarization observed both for
asteroids and comets, a unified approach has been proposed. Since the
homogeneous particles, even of irregular shape, mostly do not demonstrate
this peculiarity, we considered the scatters as aggregates composed of
monomers of the wavelength size. Although the regolith grains are known to
be much larger than the particles discussed here, the experiments showed that
namely the surface irregularities comparable to the wavelength induce the
negative branch of polarization. The aggregate model explains the main
features of the phase and spectral dependence of the polarization observed for
comets and asteroids.