Spitzer observations of the asteroid-comet transition object and potential spacecraft target 107P (4015) Wilson-Harrington

¹ Instituto de Astrofísica de Canarias, c/vía Láctea s/n, 38200 La Laguna, Tenerife, Spain e-mail: jlicandr@iac.es
² Departamento de Astrofísica, Universidad de La Laguna, 38205 La Laguna, Tenerife, Spain
³ Physics Department, University of Central Florida, Orlando, FL, 32816, USA
⁴ Department of Astronomy, University of Maryland, College Park, MD 20742-2421, USA
⁵ UNS, CNRS, Observatoire de la Côte d'Azur, Nice, France
⁶ IPAC, MS 220-6, Caltech, Pasadena, CA, 91125, USA
⁷ Laboratoire d'Astrophysique de Marseille, CNRS & Université de Provence, 13388 Marseille Cedex 13, France
⁸ Konkoly Obs., PO Box 67, 1525, Hungary
⁹ Dept. of Astronomy, Univ. of Maryland, College Park, MD, 20742, USA
¹⁰ NASA/JPL, 4800 Oak Grove Dr., Pasadena, CA, 91109, USA
¹¹ Centre for Astrophysics and Planetary Science, Univ. of Kent, Canterbury CT2 7NH, UK
¹² Astrophysics Research Centre, Queens Univ. Belfast, Belfast, BT7 1NN, UK
¹³ Johns Hopkins Univ. Applied Physics Lab., 11100 Johns Hopkins Rd, Laurel, MD, 20723, USA
¹⁴ Inst. for Astronomy, Univ. of Hawaii, 2680 Woodlawn Dr., Honolulu, HI 96822, USA
¹⁵ Astronomical Institute, Slovak Academy of Sciences, Slovak Republic, 845 04 Bratislava, Slovakia
¹⁶ ESO, Alonso de Córdova 3107, Vitacura, Santiago, Chile

Received: 13 August 2009
Accepted: 21 September 2009

Abstract

Context. Near-Earth asteroid-comet transition object 107P/ (4015) Wilson-Harrington is a possible target of the joint European Space Agency (ESA) and Japanese Aerospace Exploration Agency (JAXA) Marco Polo sample return mission. Physical studies of this object are relevant to this mission, and also to understanding its asteroidal or cometary nature.

Aims. Our aim is to obtain significant new constraints on the surface thermal properties of this object.

Methods. We present mid-infrared photometry in two filters (16 and 22 μm) obtained with NASA's Spitzer Space Telescope on February 12, 2007, and results from the application of the Near Earth Asteroid Thermal Model (NEATM). We obtained high S/N in two mid-IR bands allowing accurate measurements of its thermal emission.

Results. We obtain a well constrained beaming parameter (η = 1.39±0.26) and obtain a diameter and geometric albedo of D = 3.46±0.32 km, and p_V = 0.059±0.011. We also obtain similar results when we apply this best-fitting thermal model to single-band mid-IR photometry reported by Campins et al. (1995, P&SS, 43, 733), Kraemer et al. (2005, AJ, 130, 2363) and Reach et al. (2007, Icarus, 191, 298).

Conclusions. The albedo of 4015 Wilson-Harrington is low, consistent with those of comet nuclei and primitive C-, P-, D-type asteorids. We establish a rough lower limit for the thermal inertia of W-H of 60 Jm^-2s^-0.5 K^-1 when it is at  AU, which is slightly over the limit of 30 Jm^-2 s^-0.5 K^-1 derived by Groussin et al. (2009, Icarus, 199, 568) for the thermal inertia of the nucleus of comet 22P/Kopff.