Multi-wavelength observations of Asteroid 2100 Ra-Shalom

Abstract

We observed near-Earth asteroid (NEA) 2100 Ra-Shalom over a six-year period, obtaining rotationally resolved spectra in the visible, near-infrared, thermal-infrared, and radar wavelengths. We find that Ra-Shalom has an effective diameter of D eff = 2.3 ± 0.2 km , rotation period P = 19.793 ± 0.001 h , visual albedo p v = 0.13 ± 0.03 , radar albedo σ ˆ OC = 0.36 ± 0.10 , and polarization ratio μ c = 0.25 ± 0.04 . We used our radar observations to generate a three-dimensional shape model which shows several structural features of interest. Based on our thermal observations, Ra-Shalom has a high thermal inertia of ∼10 3 J m −2 s −0.5 K −1, consistent with a coarse or rocky surface and the inferences of others [Harris, A.W., Davies, J.K., Green, S.F., 1998. Icarus 135, 441–450; Delbo, M., Harris, A.W., Binzel, R.P., Pravec, P., Davies, J.K., 2003. Icarus 166, 116–130]. Our spectral data indicate that Ra-Shalom is a K-class asteroid and we find excellent agreement between our spectra and laboratory spectra of the CV3 meteorite Grosnaja. Our spectra show rotation-dependent variations consistent with global variations in grain size. Our radar observations show rotation-dependent variations in radar albedo consistent with global variations in the thickness of a relatively thin regolith.