“TNOs are Cool”: A survey of the trans-Neptunian region

Abstract

The goal of the Herschel open time key programme "TNOs are Cool!" is to derive the physical and thermal properties for a large sample of Centaurs and trans-Neptunian objects (TNOs), including resonant, classical, detached and scattered disk objects. We present results for seven targets either observed in PACS point-source, or in mini scan-map mode. Spitzer-MIPS observations were included for three objects. The sizes of these targets range from 100 km to almost 1000 km, five have low geometric albedos below 10%, (145480) 2005 TB 190 has a higher albedo above 15%. Classical thermal models driven by an intermediate beaming factor of η = 1.2 or η-values adjusted to the observed colour temperature fit the multi-band observations well in most cases. More sophisticated thermophysical models give very similar diameter and albedo values for thermal inertias in the range 0−25 J m −2 s −0.5 K −1 , consistent with very low heat conductivities at temperatures far away from the Sun. The early experience with observing and model strategies will allow us to derive physical and thermal properties for our complete Herschel TNO sample of 140 targets as a benchmark for understanding the solar system debris disk, and extra-solar ones as well.

“TNOs are Cool”: A survey of the trans-Neptunian region

“…This detached object was not observed by Spitzer-MIPS, but was already measured in chopnod mode by Herschel. Our new results, using a fixed-η mode (D = 464 ± 62 km, p V = 14.8 +5.1 −3.6 %) are reasonably consistent (to within 1-σ) with the preliminary values published by Müller et al (2010) (D = 375 ± 45 km, p V = 19.0 ± 5.0%). 10 .…”

“…Hence a general conclusion is that unless they are very rough, KBO surfaces must have very low thermal conductivity, suggesting a high degree of surface porosity. Similar thermal inertias and η's for KBOs were obtained in Müller et al (2010).…”

“…This requires the use of a thermal model to calculate the disk-integrated thermal emission. Here we use the so-called hybrid standard thermal model (hybrid STM, Müller et al 2010;Stansberry et al 2008). Except for the fact that the hybrid STM assumes zero phase angle (which is an excellent approximation for TNOs), it is identical to the NearEarth Asteroid Thermal Model (NEATM, Harris 1998).…”

“…More physical models (e.g. TPM) may lead to somewhat different values and error bars, as illustrated by Müller et al (2010) in the case of a few objects observed in the Science Demonstration Phase (SDP) of the "TNOs are cool" programme.…”

“…The launch of Herschel Space Observatory in 2009 offered a new tool for this purpose, providing photometry over 6 bands from 70-500 μm. Early results on a handful of objects were presented in Müller et al (2010), Lim et al (2010), and Lellouch et al (2010). Beyond their intrinsic scientific value, albedos are needed to properly interpret reflectance spectra.…”