Physical properties of the ESA Rosetta target asteroid (21) Lutetia
LESIA, Observatoire de Paris
, 5 place Jules Janssen,
2 Université Paris 7 Denis-Diderot, 5 rue Thomas Mann, 75205 Paris Cedex, France
3 Tampere University of Technology, PO Box 553, 33101 Tampere, Finland
4 Southwest Research Institute, 1050 Walnut St. #300, Boulder, CO 80302, USA
5 Starfire Optical Range, Directed Energy Directorate, Air Force Research Laboratory, Kirtland AFB, NM 87117-577, USA
6 W.M. Keck Observatory, 65-1120 Mamalahoa Highway, Kamuela, HI 96743, USA
7 Johns Hopkins University Applied Physics Laboratory, Laurel, MD 20723-6099, USA
8 European Southern Observatory, Alonso de Córdova 3107, Vitacura, Casilla 19001, Santiago de Chile, Chile
9 IMCCE, Observatoire de Paris, 14 bvd de l’Observatoire, 75014 Paris, France
10 Gemini Observatory, Northern Operations Center, 670 N. A’ohoku Place, Hilo, HI, 96720, USA
11 INAF, Osservatorio Astronomico di Roma, via Frascati 33, 00040 Monteporzio Catone (Roma), Italy
12 Dipartimento di Fisica, Università di Roma Tor Vergata, via della Ricerca Scientifica 1, 00133 Roma, Italy
13 Les Engarouines Observatory, 84570 Mallemort-du-Comtat, France
14 Geneva Observatory, 1290 Sauverny, Switzerland
15 Astronomical Observatory, Adam Mickiewicz University, Sloneczna 36, 60-286 Poznan, Poland
16 Blauvac Observatory, 84570 St-Estève, France
17 Observatorio Montcabre, C/Jaume Balmes 24, 08348 Cabrils, Barcelona, Spain
18 Le Cres Observatory, 2 rue des Écoles, 34920 le Cres, France
19 Wiggins Observatory, 472 Country Club, Tooele Utah 84074, USA
Received: 28 May 2010
Accepted: 26 August 2010
Aims. We determine the physical properties (spin state and shape) of asteroid (21) Lutetia, target of the International Rosetta Mission of the European Space Agency, to help in preparing for observations during the flyby on 2010 July 10 by predicting the orientation of Lutetia as seen from Rosetta.
Methods. We use our novel KOALA inversion algorithm to determine the physical properties of asteroids from a combination of optical lightcurves, disk-resolved images, and stellar occultations, although the last are not available for (21) Lutetia.
Results. We find the spin axis of (21) Lutetia to lie within 5° of (λ = 52°, β = − 6°) in the Ecliptic J2000 reference frame (equatorial α = 52°, δ = + 12°), and determine an improved sidereal period of 8.168270 ± 0.000001 h. This pole solution implies that the southern hemisphere of Lutetia will be in “seasonal” shadow at the time of the flyby. The apparent cross-section of Lutetia is triangular when seen “pole-on” and more rectangular “equator-on”. The best-fit model suggests there are several concavities. The largest of these is close to the north pole and may be associated with strong impacts.
Key words: minor planets, asteroids: individual: (21) Lutetia / methods: observational / techniques: high angular resolution / instrumentation: adaptive optics
Based on observations collected at the W. M. Keck Observatory and at European Southern Observatory Very Large Telescope (program ID:079.C-0493, PI: E. Dotto). The W. M. Keck Observatory is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation.
Tables 1, 2, 4 and Figs. 3–5 are only available in electronic form at http://www.aanda.org
© ESO, 2010