Physical properties of ESA Rosetta target asteroid (21) Lutetia: Shape and flyby geometry

Benoit Carry (1) , Mikko Kaasalainen (2) , Cedric Leyrat (1) , William J. Merline (3) , Jack D. Drummond (4) , Al Conrad (5) , Hal A. Weaver (6) , Peter M. Tamblyn (3) , Clark R. Chapman (3) , Christophe Dumas (7) , Francois Colas (8) , Julian C. Christou (9) , Elisabetta Dotto (10) , Davide Perna (1, 10, 11) , Sonia Fornasier (1) , Laurent Bernasconi (12) , Raoul Behrend (13) , Frédéric Vachier (8) , Agnieszka Kryszczynska (14) , Magdalena Polinska (14) , Marcello Fulchignoni (1) , Rene Roy (15) , Ramon Naves (16) , Raymond Poncy (17) , Patrick Wiggins (18)

1 LESIA - Laboratoire d'études spatiales et d'instrumentation en astrophysique
2 TUT - Tampere University of Technology [Tampere]
3 SwRI - Southwest Research Institute [Boulder]
4 Starfire Optical range
5 W.M. Keck Observatory
6 APL - Johns Hopkins University Applied Physics Laboratory [Laurel, MD]
7 ESO - European Southern Observatory
8 IMCCE - Institut de Mécanique Céleste et de Calcul des Ephémérides
9 Gemini Observatory
10 IASF-Roma - Istituto di Astrofisica Spaziale e Fisica cosmica - Roma
11 Dipartimento di Fisica
12 Les Engarouines Observatory
13 Geneva Observatory
14 Astronomical Observatory [Poznan]
15 Blauvac Obsevatory
16 Observatorio Montcabre
17 Le Cres Observatory
18 Wiggins Observatory

Aims. We determine the physical properties (spin state and shape) of asteroid (21) Lutetia, target of the ESA Rosetta mission, 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 latter are not available for (21) Lutetia. Results. We find the spin axis of (21) Lutetia to lie within 5 degrees of ({\lambda} = 52 deg., {\beta} = -6 deg.) in Ecliptic J2000 reference frame (equatorial {\alpha} = 52 deg., {\delta} = +12 deg.), and determine an improved sidereal period of 8.168 270 \pm 0.000 001 h. This pole solution implies the southern hemisphere of Lutetia will be in "seasonal" shadow at the time of the flyby. The apparent cross-section of Lutetia is triangular as seen "pole-on" and more rectangular as seen "equator-on". The best-fit model suggests the presence of several concavities. The largest of these is close to the north pole and may be associated with large impacts.

Mots clés: methods: observational; asteroids: individual: (21) Lutetia; techniques: high angular resolution; instrumentation: adaptive optics; minor planets; asteroids; individual; (21) Lutetia -methods; observational -techniques; high angular resolutioninstrumentation; adaptive optics

Domaines: Planétologie et astrophysique de la terre [astro-ph.EP]; Planétologie et astrophysique de la terre [astro-ph.EP]

Benoit Carry, Mikko Kaasalainen, Cedric Leyrat, William J. Merline, Jack D. Drummond, et al.. Physical properties of ESA Rosetta target asteroid (21) Lutetia: Shape and flyby geometry. Astronomy and Astrophysics - A&A, 2010, 523 (A94), 19 p. ⟨10.1051/0004-6361/201015074⟩. ⟨hal-00618654⟩