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W.M. Grundy (Lowell Obs.), J.R. Spencer (SwRI), J.A. Stansberry (U. Arizona), M.W. Buie (Lowell Obs.), E.I. Chiang (U.C. Berkeley), D.P. Cruikshank (NASA Ames), R.L. Millis, L.H. Wasserman (Lowell Obs.)
We report on a Spitzer Space Telescope program observing 24 and 70~\mum thermal radiation from classical Kuiper belt objects (KBOs) using the Multiband Imaging Photometer for Spitzer (MIPS). KBOs are a sub-population of trans-neptunian objects (TNOs) having non-resonant orbits with relatively small inclinations and eccentricities. Their orbits may be among the least dynamically altered of TNO orbits and so may offer more knowledge about where they formed than can be derived from the orbits of TNOs in more perturbed dynamical classes. Owing to their distant perihelia, and thus lower anticipated thermal fluxes, classical KBOs (especially those having the least inclined and eccentric orbits) are poorly represented in other Spitzer TNO surveys. Another TNO sub-population with a potentially knowable formation region is the Neptune Trojans, so we included Neptune Trojan 2001~QR322 in our sample.
Preliminary results from this ongoing Spitzer/MIPS survey include evidence for higher albedos than had been previously assumed. Higher albedos mean smaller diameters and thus lower thermal fluxes, making detection far more difficult than anticipated. To date, we have obtained mostly marginal detections and upper limits. Only the Neptune Trojan, being closer and warmer than the KBOs, has been firmly detected at 24~\mum. We will also discuss issues encountered in pushing the sensitivity limits of the MIPS instrument, and in interpreting thermal observations of objects much colder than the main belt asteroids for which the radiometric size determination technique was originally developed and calibrated.
Spitzer Space Telescope is operated by the Jet Propulsion Laboratory, California Institute of Technology under NASA contract 1407\null. This work is supported by NASA through JPL/Caltech Contract Number #1265877.
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Bulletin of the American Astronomical Society, 37 #3
© 2004. The American Astronomical Soceity.