Thermal Properties Of Trans-neptunian Objects And Centaurs From Combined Herschel And Spitzer Observations

Abstract

We present a study of the thermal properties of about 70 trans-Neptunian objects (TNOs) and Centaurs observed with Herschel Space Observatory (either PACS or PACS/SPIRE) and Spitzer (MIPS). The combined wavelength range is 24-160 μm and additionally up to 500 μm for a few targets. We apply radiometric modeling techniques (NEATM) to the measured fluxes to derive diameter, albedo and beaming factor (η). The latter parameter is a proxy for the combined effects of surface thermal properties (thermal inertia), surface roughness, and rotation properties. We examine the results and search for trends in the inferred η values with several parameters, including heliocentric distance, albedo, and rotational properties. In particular, the distribution of η as a function of heliocentric distance reveals a large dispersion in the η values, but also shows that there are no objects with large beaming factors at low distances. This is an expected ensemble behaviour for a population of objects with low thermal inertia (probably less than 0-20 J m‑2 s‑1/2 K‑1), consistent with thermo-physical modeling of a few selected objects, which suggests that these objects are covered with low-conductivity regolith