Abstract
Abstract We present an analysis of Hapke photometric modeling applied to uniform ground-based UBVRIJHK broadband data of asteroid 25143 Itokawa collected over a wide range of solar phase angles (4°–130°) during the 2004 apparition (Thomas-Osip et al., this issue, hereafter Paper I). Our photometric analyses indicate that Itokawa has a blocky surface with properties different from other, albeit larger, S-class asteroids studied using similar Hapke modeling analyses. Images from the Hayabusa spacecraft affirm the Hapke modeling results, demonstrating the ability of Hapke photometric modeling to predict a rocky asteroid surface correctly; this is the first time that a predicted rocky surface has been observed by a spacecraft. The single particle scattering functions are dominantly forward scattering, suggesting the surface material is composed primarily of clear particles whose scattering is dictated by the particle’s surface as opposed to internal scatterers (more typical of S-class asteroids), while the opposition parameters indicate that the regolith may be more compact than most of the limited number of asteroids visited by spacecraft to date. The roughness properties, single particle scattering properties, and opposition surge characteristics are all indicative of a surface where multiple scattering does not play a major role in defining the photometric properties of the regolith.
Highlights
The Japanese spacecraft Hayabusa encountered and gathered data of its near-Earth asteroid target, Itokawa, from September until early December, 2005
Conventional theory about “space weathering” suggests that S-class asteroids are comprised of mafic silicate minerals similar to those minerals found in ordinary chondrites, and a thin layer of surface material altered by some form of space weathering to produce the redder reflectance spectra with shallower absorption features observed today (c.f., Clark et al, 2002a; Chapman, 1996; Pieters et al, 2000)
A small asteroid that looks very different from any other asteroid visited by a spacecraft, indicate that its physical surface properties differ from typical S-class asteroids, its color photometry is consistent with average, albeit larger, S-class asteroids
Summary
The Japanese spacecraft Hayabusa encountered and gathered data of its near-Earth asteroid target, Itokawa, from September until early December, 2005. In an effort to understand the physical characteristics of this asteroid, and thereby aid the Hayabusa mission, we obtained an extensive broadband UBVRIJHK filter dataset of Itokawa in 2004, designed to provide optimal corrected solar phase curves for robust Hapke modeling of the surface scattering properties Thomas-Osip et al (Paper I) derived solar phase curves in units of absolute magnitude for eight colors (U–K) using the 2004 apparition observations. These solar phase curves were corrected for rotational phase curve variations and represent brightness variations as a function of solar phase angle (Sun-asteroid-Earth) only.
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