We present a method for analyzing the reflectance properties of atmosphereless bodies as asteroids and comet nuclei. The method is self-consistent, independent of the shape model of the object and can be easily applied for any space mission target. We used it for the E-type Main Belt asteroid (2867) Steins, observed from the OSIRIS-WAC camera onboard Rosetta spacecraft during a close approach on September 5, 2008. We investigate the reflectance dependence on phase angle which is interpreted in terms of the Hapke's theory of bidirectional reflectance. A deeper analysis allows to obtain an estimate of the typical size of the regolith grains. Steins regolith layer seems to be made of large, highly scattering iron-poor opaque silicate particles. The macroscopic roughness, probably influenced by the global irregular shape, appears fairly high, comparable with radar measurements of other E-type asteroids. Assuming an enstatite composition, we estimated a grain size of about 30-130 μm and we noticed a correlation between grain size and wavelength, suggesting the existence of a grain size distribution, as expected from real surfaces. The comparison with more accurate calculations (Spjuth et al., 2009) shows that our simplified method is robust and reliable for a preliminary and shape-independent analysis of the reflectance properties of atmosphereless bodies.
Photometric analysis of asteroid (2867) steins from rosetta OSIRIS images
Bertini I.;
2012-01-01
Abstract
We present a method for analyzing the reflectance properties of atmosphereless bodies as asteroids and comet nuclei. The method is self-consistent, independent of the shape model of the object and can be easily applied for any space mission target. We used it for the E-type Main Belt asteroid (2867) Steins, observed from the OSIRIS-WAC camera onboard Rosetta spacecraft during a close approach on September 5, 2008. We investigate the reflectance dependence on phase angle which is interpreted in terms of the Hapke's theory of bidirectional reflectance. A deeper analysis allows to obtain an estimate of the typical size of the regolith grains. Steins regolith layer seems to be made of large, highly scattering iron-poor opaque silicate particles. The macroscopic roughness, probably influenced by the global irregular shape, appears fairly high, comparable with radar measurements of other E-type asteroids. Assuming an enstatite composition, we estimated a grain size of about 30-130 μm and we noticed a correlation between grain size and wavelength, suggesting the existence of a grain size distribution, as expected from real surfaces. The comparison with more accurate calculations (Spjuth et al., 2009) shows that our simplified method is robust and reliable for a preliminary and shape-independent analysis of the reflectance properties of atmosphereless bodies.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
