Astronomy and Astrophysics – Astronomy
Scientific paper
Sep 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006dps....38.3401s&link_type=abstract
American Astronomical Society, DPS meeting #38, #34.01; Bulletin of the American Astronomical Society, Vol. 38, p.546
Astronomy and Astrophysics
Astronomy
2
Scientific paper
The densities of Kuiper Belt objects provide valuable clues to their composition, internal structure, and origin. To extend our limited knowledge of KBO densities, we have been attempting to obtain radiometric diameters for binary KBOs, which have masses determined from the satellite orbits, using the MIPS mid-IR imager on the Spitzer Space Telescope. Due to higher than expected KBO albedos, and MIPS's lower than expected 70 µm sensitivity, our 2006 campaign concentrated on long exposures on a single target, (26308) 1998 SM165, one of the brightest and warmest known KBO binaries. 7.5 hour integration times at both 24 and 70 µm yielded monochromatic fluxes of 0.11 ± 0.01 mJy at 23.7 microns and 6.1 ± 1.1 mJy at 71.4 microns. From these we derive a relatively model-independent diameter of 287 ± 36 km for the primary and 96 ± 12 km for the satellite, assuming similar albedos. The derived V geometric albedo (using HV = 6.13, Romanishin and Tegler 2006 Icarus 179 523) is 0.07 ± 0.02. The system mass from HST (Margot et al. 2004, DPS 36, 08.03) then yields a system density of 0.51 +0.29 -0.14 g cm-3, comparable to that for KBO (47171) 1999 TC36 (Stansberry et al. 2006, Ap. J. 643, 556). This density is also comparable to that of the similarly-sized planetary satellites Amalthea (D=200 km, ρ=0.86) and Hyperion (D=250 km, ρ=0.6), but much lower than the density of Phoebe (D=200 km, ρ=1.63), and suggests both high porosity and a dominantly water ice composition for this KBO, despite its low albedo and red color. Supporting visible-wavelength lightcurve observations obtained at Lowell Observatory also yielded a revised rotation rate of 8.40 ± 0.05 hours for 1998 SM165.
Grundy Will M.
Noll Keith S.
Spencer John Robert
Stansberry John Arthur
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