A radar survey of M- and X-class asteroids

Shepard, Michael K.; Clark, B. E.; Nolan, M. C.; Howell, E. S.; Magri, C.; Giorgini, Jon D.; Benner, L. A. M.; Ostro, S. J.; Harris, Alan W.; Warner, Brian D.; Pray, Donald P.; Pravec, Petr; Fauerbach, M.; Bennett, Thomas; Klotz, A.; Behrend, R.; Correia, Horacio; Coloma, J. M.; Casulli, Silvano; Rivkin, A. S.

doi:10.1016/j.icarus.2007.11.032

Cited by 80 publications

(104 citation statements)

References 42 publications

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“…Lutetia's radar albedo is lower than for the largely metallic asteroids but is somewhat higher than for typical CCs (13%±5% for the average C-class object, according to Shepard et al 2008).…”

Section: Discussionmentioning

confidence: 81%

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

Weaver¹,

Feldman²,

Merline³

et al. 2010

A&A

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Context. The asteroid (21) Lutetia is the target of a planned close encounter by the Rosetta spacecraft in July 2010. To prepare for that flyby, Lutetia has been extensively observed by a variety of astronomical facilities. Aims. We used the Hubble Space Telescope (HST) to determine the albedo of Lutetia over a wide wavelength range, extending from ∼1500 Å to ∼7000 Å. Methods. Using data from a variety of HST filters and a ground-based visible light spectrum, we employed synthetic photometry techniques to derive absolute fluxes for Lutetia. New results from ground-based measurements of Lutetia's size and shape were used to convert the absolute fluxes into albedos. Results. We present our best model for the spectral energy distribution of Lutetia over the wavelength range 1200−8000 Å. There appears to be a steep drop in the albedo (by a factor of ∼2) for wavelengths shorter than ∼3000 Å. Nevertheless, the far ultraviolet albedo of Lutetia (∼10%) is considerably larger than that of typical C-chondrite material (∼4%). The geometric albedo at 5500 Å is 16.5 ± 1%. Conclusions. Lutetia's reflectivity is not consistent with a metal-dominated surface at infrared or radar wavelengths, and its albedo at all wavelengths (UV-visibile-IR-radar) is larger than observed for typical primitive, chondritic material. We derive a relatively high FUV albedo of ∼10%, a result that will be tested by observations with the Alice spectrograph during the Rosetta flyby of Lutetia in July 2010.

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Section: Discussionmentioning

confidence: 81%

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

Weaver¹,

Feldman²,

Merline³

et al. 2010

A&A

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“…Carvano et al (2008) later derived a lower albedo from ground-based observations, seemingly incompatible with previous works. 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: Introductionmentioning

confidence: 67%

“…Lutetia has been extensively studied using spectroscopy in the visible, near-and mid-infrared and its albedo measured by polarimetry and thermal radiometry (McCord & Chapman 1975;Chapman et al 1975;Zellner & Gradie 1976;Bowell et al 1978;Rivkin et al 1995;Magri et al 1999;Rivkin et al 2000;Lazzarin et al 2004;Barucci et al 2005;Birlan et al 2006;Nedelcu et al 2007;Barucci et al 2008;Shepard et al 2008;DeMeo et al 2009;Vernazza et al 2009;Lazzarin et al 2009Lazzarin et al , 2010Perna et al 2010;Belskaya et al 2010). We present a discussion on Lutetia's taxonomy and composition in a companion paper (Drummond et al 2010).…”

Section: Introductionmentioning

confidence: 99%

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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“…Radar observations of Lutetia (Magri et al (1999(Magri et al ( , 2007, confirmed by Shepard et al (2008)) showed that Lutetia has a moderate radar albedo (0.19−0.24), comfortably in the midrange of ECs, but considerably lower than metallic M-types and higher than most CCs. The uncertainty range in these values overlaps with some CO/CV carbonaceous chondrites compositions at the low extreme and with some metallic compositions at the high end.…”

Section: Taxonomy and Densitymentioning

confidence: 84%

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

Drummond¹,

Conrad

Merline

et al. 2010

A&A

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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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A radar survey of M- and X-class asteroids

Cited by 80 publications

References 42 publications

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

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

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

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

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