Letter to the Editor

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

I. Results from the Herschel science demonstration phase (SDP)

¹ Max-Planck-Institut für extraterrestrische Physik (MPE), Giessenbachstrasse, 85748 Garching, Germany e-mail: tmueller@mpe.mpg.de
² Observatoire de Paris, Laboratoire d'Études Spatiales et d'Instrumentation en Astrophysique (LESIA), 5 place Jules Janssen, 92195 Meudon Cedex, France
³ The University of Arizona, Tucson AZ 85721, USA
⁴ Konkoly Observatory of the Hungarian Academy of Sciences, 1525 Budapest, PO Box 67, Hungary
⁵ Max-Planck-Institut für Sonnensystemforschung (MPS), Max-Planck-Straße 2, 37191 Katlenburg-Lindau, Germany
⁶ Observatoire de la Côte d'Azur, laboratoire Cassiopée B.P. 4229; 06304 Nice Cedex 4, France
⁷ Laboratoire d'Astrophysique de Marseille, CNRS & Université de Provence, 38 rue Frédéric Joliot-Curie, 13388 Marseille Cedex 13, France
⁸ Instituto de Astrofísica de Andalucía (CSIC) C/ Camino Bajo de Huétor, 50, 18008 Granada, Spain
⁹ Observatoire de Paris, Laboratoire d'Études Spatiales et d'Instrumentation en Astrophysique (LESIA), University of Paris 7 “Denis Diderot”, 4 rue Elsa Morante, 75205 Paris Cedex, France
¹⁰ Deutsches Zentrum für Luft- und Raumfahrt, Berlin-Adlershof, Rutherfordstraße 2, 12489 Berlin-Adlershof, Germany
¹¹ Department of Physics and Astronomy, Science Laboratories, University of Durham, South Road, Durham, DH1 3LE, UK
¹² Newton Fellow of the Royal Society, Astrophysics Research Centre, Physics Building, Queen's University, Belfast, County Antrim, BT7 1NN, UK
¹³ Space Science and Technology Department, Science and Technology Facilities Council, Rutherford Appleton Laboratory, Harwell Science and Innovation Campus, Didcot, Oxon UK, OX11 0QX, UK
¹⁴ Northern Arizona University, Department of Physics & Astronomy, PO Box 6010, Flagstaff, AZ 86011, USA
¹⁵ INAF - Osservatorio Astronomico di Roma, via di Frascati 33, 00040 Monte Porzio Catone, Italy
¹⁶ ESO, Karl-Schwarzschild-Str. 2, 85748 Garching, Germany
¹⁷ IMCCE/Observatoire de Paris, CNRS, 77 Av. Denfert-Rochereau, 75014 Paris, France
¹⁸ Herschel Science Centre (HSC), European Space Agency (ESA), European Space Astronomy Centre (ESAC), Camino bajo del Castillo, s/n, Urbanizacion Villafranca del Castillo, Villanueva de la Cañada, 28692 Madrid, Spain
¹⁹ Universität Bern, Hochschulstrasse 4, 3012 Bern, Switzerland

Received: 31 March 2010
Accepted: 15 May 2010

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 TB₁₉₀ 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.