Ultraviolet and visible photometry of asteroid (21) Lutetia using the Hubble Space Telescope

Weaver, H. A.; Feldman, P. D.; Merline, W. J.; Mutchler, Max; A’Hearn, Michael F.; Bertaux, Jean-Loup; Feaga, Lori M.; Parker, J. W.; Slater, D. C.; Steffl, A. J.; Chapman, C. R.; Drummond, Jack D.; Stern, S. A.

doi:10.1051/0004-6361/200913950

Cited by 20 publications

(23 citation statements)

References 33 publications

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“…Radar data analyzed by Magri et al (1999Magri et al ( , 2007 yielded an effective diameter for Lutetia of 116 km; reinterpretation of those data and new radar observations (Shepard et al 2008) suggest an effective diameter of 100 ± 11 km and an associated visual albedo of 0.20. Recent HST observations of Lutetia (Weaver et al 2010) indicate a visual albedo of about 16%, a result based partly on the size/shape/pole determinations from our work in the present paper and from that of Drummond et al (2010).…”

Section: Introductionsupporting

confidence: 69%

Physical properties of the ESA Rosetta target asteroid (21) Lutetia

Carry

Kaasalainen

Leyrat

et al. 2010

A&A

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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 8.168 270±0.000 001 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.

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Section: Introductionsupporting

confidence: 69%

Physical properties of the ESA Rosetta target asteroid (21) Lutetia

Carry

Kaasalainen

Leyrat

et al. 2010

A&A

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“…The radiometry by Mueller et al (2006), reduced using two different thermal models, also yields albedos too high for most CC meteorites. A recent determination of visual albedo, using Hubble Space Telescope observations (Weaver et al 2010) and the size/shape/pole results from the present paper and Carry et al (2010b), indicate a value near 16%. This value, consistent with EC albedos (as well as metallic), is generally higher than most CCs, although some types of CCs, namely CO/CVs, have higher albedos, typically about 10%, with some COs getting as high as 15−17% (Clark et al 2009).…”

Section: Taxonomy and Densitysupporting

confidence: 59%

Physical properties of the ESA Rosetta target asteroid (21) Lutetia

Drummond¹,

Conrad

Merline

et al. 2010

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Context. Asteroid (21) Lutetia was the target of the ESA Rosetta mission flyby in 2010 July. Aims. We seek the best size estimates of the asteroid, the direction of its spin axis, and its bulk density, assuming its shape is well described by a smooth featureless triaxial ellipsoid. We also aim to evaluate the deviations from this assumption. Methods. We derive these quantities from the outlines of the asteroid in 307 images of its resolved apparent disk obtained with adaptive optics (AO) at Keck II and VLT, and combine these with recent mass determinations to estimate a bulk density. Results. Our best triaxial ellipsoid diameters for Lutetia, based on our AO images alone, are a × b × c = 132 × 101 × 93 km, with uncertainties of 4 × 3 × 13 km including estimated systematics, with a rotational pole within 5The AO model fit itself has internal precisions of 1 × 1 × 8 km, but it is evident both from this model derived from limited viewing aspects and the radius vector model given in a companion paper, that Lutetia significantly departs from an idealized ellipsoid. In particular, the long axis may be overestimated from the AO images alone by about 10 km. Therefore, we combine the best aspects of the radius vector and ellipsoid model into a hybrid ellipsoid model, as our final result, of diameters 124 ± 5 × 101 ± 4 × 93 ± 13 km that can be used to estimate volumes, sizes, and projected areas. The adopted pole position is withinConclusions. Using two separately determined masses and the volume of our hybrid model, we estimate a density of 3.5 ± 1.1 or 4.3 ± 0.8 g cm −3 . From the density evidence alone, we argue that this favors an enstatite-chondrite composition, although other compositions are formally allowed at the extremes (low-porosity CV/CO carbonaceous chondrite or high-porosity metallic). We discuss this in the context of other evidence.

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“…Taking the various uncertainties in the measurements into account, in the models (and assumed parameters), in the empirical calibrations, and of paramount importance, distinguishing between albedos with and without opposition effect, most if not all reported values can be reconciled. We are confident that our determinations based on accurate space photometry and on the most advanced shape model, and which further agree with the recent results of Belskaya et al (2010) and of Weaver et al (2010), reflect the real properties of the surface of Lutetia.…”

Section: The (H − G)supporting

confidence: 90%

“…It should be compared to our determination using the H-G phase function p V = 0.18 ± 0.02, and both determinations agree within their error bars. Weaver et al (2010) used a method similar to ours, combining photometry performed with the Hubble space telescope with the ellipsoid shape model of Drummond et al (2010). They obtained p V = 0.16 with an uncertainty dominated by the shape model and therefore close to ours, that is, ∼0.02.…”

Section: The (H − G)mentioning

confidence: 99%

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Multi-color, rotationally resolved photometry of asteroid 21 Lutetia from OSIRIS/Rosetta observations

Lamy¹,

Faury²,

Jordá³

et al. 2010

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Context. Asteroid 21 Lutetia is the second target of the Rosetta space mission. Extensive pre-encounter, space-, and ground-based observations are being performed to prepare for the flyby in July 2010. Aims. The aim of this article is to accurately characterize the photometric properties of this asteroid over a broad spectral range from the ultraviolet to the near-infrared and to search for evidence of surface inhomogeneities. Methods. The asteroid was imaged on 2 and 3 January 2007 with the Narrow Angle Camera (NAC) of the Optical, Spectroscopic, and Infrared Remote Imaging System (OSIRIS) during the cruise phase of the Rosetta spacecraft. The geometric conditions were such that the aspect angle was 44 • (i.e., mid-northern latitudes) and the phase angle 22.4 • . Lutetia was continuously monitored over 14.3 h, thus exceeding one rotational period and a half, with twelve filters whose spectral coverage extended from 271 to 986 nm. An accurate photometric calibration was obtained from the observations of a solar analog star, 16 Cyg B. Results. High-quality light curves in the U, B, V, R and I photometric bands were obtained. Once they were merged with previous light curves from over some 45 years, the sidereal period is accurately determined: P rot = 8.168271 ± 0.000002 h. Color variations with rotational phase are marginally detected with the ultraviolet filter centered at 368 nm but are absent in the other visible and near-infrared filters. The albedo is directly determined from the observed maximum cross-section obtained from an elaborated shape model that results from a combination of adaptive-optics imaging and light curve inversion. Using current solutions for the phase function, we find geometric albedos p V = 0.130 ± 0.014 when using the linear phase function and p V (H − G) = 0.180 ± 0.018 when using the (H − G) phase function, which incorporates the opposition effect. The spectral variation of the reflectance indicates a steady decrease with decreasing wavelength rather than a sharp fall-off.

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Ultraviolet and visible photometry of asteroid (21) Lutetia using the Hubble Space Telescope

Cited by 20 publications

References 33 publications

Physical properties of the ESA Rosetta target asteroid (21) Lutetia

Physical properties of the ESA Rosetta target asteroid (21) Lutetia

Physical properties of the ESA Rosetta target asteroid (21) Lutetia

Multi-color, rotationally resolved photometry of asteroid 21 Lutetia from OSIRIS/Rosetta observations

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