Probe the Regolith Characteristics of Asteroids from 9 yr Infrared Observations of WISE/NEOWISE: A Case Study of The Main-belt Object (656) Beagle

Abstract

This work presents the data processing, fitting procedure, modeling, and analyzing of 9 yr infrared light curves provided by the WISE/NEOWISE telescope, by which the regolith characteristics of Main-belt Object (656) Beagle is studied. Beagle locates in the Themis family, and was proposed to be the parent of the first main-belt comet (MBC) 133P. We determine Beagle’s effective diameter Deff=57.3−2.2+4.5 km, geometric albedo pv=0.05−0.007+0.004 , mean roughness θ RMS = 44 ± 4°, mean grain size b=100−90+350μm , mean specific heat capacity c p = 173 ∼ 516 J Kg−1 K−1, mean thermal conductivity κ = 0.7 ∼ 1.3 × 10−3 W m−1 K−1, and mean thermal inertia Γ = 14 ∼ 32 J m−2 s−0.5 K−1. The albedo of Beagle is a little anomalous that the albedos of Beagle’s neighboring asteroids are more close to (24) Themis, rather than Beagle itself. The W1-band near-infrared (NIR) light curves do not reveal significant heterogeneous NIR features on the surface of Beagle, being inconsistent with the expectation of a family parent that has members with diverse NIR spectral types. These results add new clues of Beagle probably being an interloper or a sister, rather than the parent of its neighboring asteroids including the famous MBC 133P, hence may lead to new scenarios about the origin of 133P. Besides, we found that asteroidal shape models from inversion of optical light curves are imperfect for modeling infrared lightcurves, thus could mislead evaluations of both the heterogeneity of regolith reflectivity at NIR and thermophysical characteristics at thermal infrared.