40 research outputs found
Character of the opposition effect and negative polarization
Photometric and polarimetric properties at small phase angles were measured for silicates with controlled surface properties in order to distinguish properties that are associated with surface reflection from those that are associated with multiple scattering from internal grain boundaries. These data provide insight into the causes and conditions of photometric properties observed at small phase angles for dark bodies of the solar system. Obsidian was chosen to represent a silicate dielectric with no internal scattering boundaries. Because obsidian is free of internal scatterers, light reflected from both the rough and smooth obsidian samples is almost entirely single and multiple Fresnel reflections form surface facets with no body component. Surface structure alone cannot produce an opposition effect. Comparison of the obsidian and basalt results indicates that for an opposition effect to occur, surface texture must be both rough and contain internal scattering interfaces. Although the negative polarization observed for the obsidian samples indicates single and multiple reflections are part of negative polarization, the longer inversion angle of the multigrain inversion samples implies that internal reflections must also contribute a significant negative polarization component
Polarimetry of transneptunian objects (136472) Makemake and (90482) Orcus
Context. We study the surface properties of transneptunian populations of
Solar-system bodies. Aims. We investigate the surface characteristics of the
dwarf planet (136472) Makemake and the resonant object (90482) Orcus. Methods.
Using the FORS2 instrument of the ESO-VLT we have carried out linear
polarisation measurements of Makemake and Orcus. Results. Polarisation of Orcus
is similar to that of smaller size objects. The polarimetric properties of
Makemake are very close to those of Eris and Pluto. We have not found any
significant differences in the polarisation properties of objects from
different dynamical classes. However, there are significant differences in
polarisation of large and smaller size objects, and between large TNOs with
water-ice and methane-ice dominated surfaces. Conclusions. We confirm the
different types of polarisation phase behavior for the largest and smaller size
TNOs. To explain subtle surface polarisation of Pluto, Makemake and Eris we
assume that their surfaces are covered by a thin layer of hoarfrost masking the
surface structure
Television pictures of Phobos: first results
In February-March 1989, 37 television images of the Martian satellite Phobos were obtained by the Phobos 2 spacecraft from distances of 200-1100 km. These images provide an important supplement to the TV data from the American Mariner 9 and Viking spacecraft in coverage of t4e surface of Phobos and in resolution in certain regions, in spectral range, and in range of phase angles. They make it possible to refine the figure and topographic and geological maps of the surface of Phobos, its spectral and angular reflective characteristics,
the surface composition and texture, and characteristics of the orbital and librational motion
Sh matrix for arbitrary scatterers Electromagnetic wave scattering from particles of arbi- trary shapes using the Sh-matrix technique
A general analytical solution of the light scattered from arbitrarily shaped particles that are represented by an expansion of a series of trigonometric functions and associated Legendre polynomials is considered. We focus here on the Gaussian random particles calculating the Shmatrix elements; the Sh-matrix approach is a variety of the T-matrix formulation