Bibcode
Landsman, Zoe; Licandro, J.; Campins, H.; Kelley, M.; Hargrove, K.; Pinilla-Alonso, N.; Cruikshank, D.; Rivkin, A. S.; Emery, J.
Bibliographical reference
American Astronomical Society, DPS meeting #42, #39.18; Bulletin of the American Astronomical Society, Vol. 42, p.1035
Advertised on:
10
2010
Citations
0
Refereed citations
0
Description
We have carried out a spectroscopic study of asteroid 65 Cybele in the 2
- 4 μm and 5 - 14 μm regions, using NASA's IRTF and Spitzer Space
Telescope, respectively. We compare these spectra with those of Trojan
asteroids and asteroid 24 Themis. Our target is the largest member of
the Cybele population; these asteroids represent a transition group
between primitive inner-main belt asteroids and Trojans, and may provide
clues to the origin of the asteroid belt and the solar system.
Our 2 - 4 μm spectrum shows a clear absorption band centered at 3.1
μm, similar to that in the spectrum of 24 Themis (Campins et al.
2010, Rivkin & Emery 2010), which can be modeled using water-ice.
Absorption bands in 65 Cybele's 3.2 - 3.6 μm region also suggest the
presence of complex organic solids. No hydrated silicates are detected.
We fit the 5 - 14 μm continuum using the NEATM (Harris 1998) and
derived a diameter D = 290 ± 5 km (consistent with Müller
and Bloemmaert 2004), beaming parameter η = 0.967 ± 0.014,
and albedo pV = 0.05 ± 0.01. Once the continuum has
been divided out, the 5 - 14 μm emissivity spectrum clearly exhibits
an emission plateau at about 9 - 12 μm with a spectral contrast of
about 5%. A similar feature is seen in the spectra of Trojan asteroids
and may be due to fine-grained silicates imbedded in a transparent
matrix, or to a very under-dense surface structure (Emery et al. 2006).
We conclude that 65 Cybele is covered by fine anhydrous silicate grains,
with a small amount of water-ice and complex organic solids. This is
similar to comets where non-equilibrium phases coexist, e.g. water-ice
and anhydrous silicates; thus we conclude that this is a very primitive
object.