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

Abstract

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 (λ = 52 deg., β = -6 deg.) in Ecliptic J2000 reference frame (equatorial α = 52 deg., δ = +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.

17 pages, 5 figures, 3 tables, submitted to Astronomy and Astrophysics

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• Near-Infrared Mapping and Physical Properties of the Dwarf-Planet Ceres
• Physical Properties of (2) Pallas
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• The triaxial ellipsoid dimensions, rotational pole, and bulk density of ESA Rosetta target asteroid (21) Lutetia
• Ultraviolet and visible photometry of asteroid (21) Lutetia using the Hubble Space Telescope
• Inhomogeneities on the surface of 21 Lutetia, the asteroid target of the Rosetta mission

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