The Rubble-Pile Asteroid Itokawa as Observed by Hayabusa

Fujiwara, Akira; Kawaguchi, Jun’ichiro; Yeomans, Donald K.; Abe, Masanao; Mukai, T.; Okada, Tatsuaki; Saito, Junji; Yano, Hajime; Yoshikawa, Makoto; Scheeres, Daniel J.; Barnouin, Olivier S.; Cheng, A.; Demura, H.; Gaskell, R. W.; Hirata, Naru; Ikeda, Hitoshi; Kominato, Takashi; Miyamoto, H.; Nakamura, Akiko; Nakamura, Ryosuke; Sasaki, Sho; Uesugi, Kentaro

doi:10.1126/science.1125841

Cited by 859 publications

(630 citation statements)

References 23 publications

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“…The small uncertainties reflect the importance of multi-epoch, multiwavelength and large phase angle coverage for thermophysical studies of small bodies. In a similar study by Müller et al (2005), also based on a large thermal data set and a shape model from lightcurve inversion techniques, the derived effective diameter agreed within 2% of the true, in-situ diameter (Müller et al 2005;Fujiwara et al 2006). The quoted uncertainties above are formal errors from the χ 2 optimization, including the possible range in thermal inertia, roughness and H V .…”

Section: Radiometric Diameter and Albedo Solutionmentioning

confidence: 78%

Thermo-physical properties of 162173 (1999 JU3), a potential flyby and rendezvous target for interplanetary missions

Müller

Ďurech

Hasegawa

et al. 2010

A&A

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Context. Near-Earth asteroid 162173 (1999 JU3) is a potential flyby and rendezvous target for interplanetary missions because of its easy-to-reach orbit. The physical and thermal properties of the asteroid are relevant for establishing the scientific mission goals and also important in the context of near-Earth object studies in general. Aims. Our goal was to derive key physical parameters such as shape, spin-vector, size, geometric albedo, and surface properties of 162173 (1999 JU3). Methods. With three sets of published thermal observations (ground-based N-band, Akari IRC, Spitzer IRS), we applied a thermophysical model to derive the radiometric properties of the asteroid. The calculations were performed for the full range of possible shape and spin-vector solutions derived from the available sample of visual lightcurve observations. Results. The near-Earth asteroid 162173 (1999 JU3) has an effective diameter of 0.87 ± 0.03 km and a geometric albedo of 0.070 ± 0.006. The χ 2 -test reveals a strong preference for a retrograde sense of rotation with a spin-axis orientation of λ ecl = 73 • , β ecl = −62 • and P sid = 7.63 ± 0.01 h. The most likely thermal inertia ranges between 200 and 600 J m −2 s −0.5 K −1 , about a factor of 2 lower than the value for 25143 Itokawa. This indicates that the surface lies somewhere between a thick-dust regolith and a rock/boulder/cm-sized, gravel-dominated surface like that of 25143 Itokawa. Our analysis represents the first time that shape and spin-vector information has been derived from a combined data set of visual lightcurves (reflected light) and mid-infrared photometry and spectroscopy (thermal emission).

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Section: Radiometric Diameter and Albedo Solutionmentioning

confidence: 78%

Thermo-physical properties of 162173 (1999 JU3), a potential flyby and rendezvous target for interplanetary missions

Müller

Ďurech

Hasegawa

et al. 2010

A&A

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“…Most asteroids are thought to have significant macroporosity (e.g., they may be rubble piles like (25143) Itokawa Fujiwara et al 2006), so the asteroid density is likely to be substantially lower than the component material density (see Britt et al 2006). If so, then metallic meteorites are still ruled out, Notes.…”

Section: Taxonomy and Densitymentioning

confidence: 99%

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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“…It means that some NEOs are not monolithic bodies but "rubble-pile" structures, which have no coherent tensile strength and are weakly held together by their own mutual gravity. One example of a "rubble-pile" body is the Apollo-object (25143) Itokawa (Fujiwara et al (2006)). …”

Section: Sizes and Densitiesmentioning

confidence: 99%

Near-Earth objects as principal impactors of the Earth: Physical properties and sources of origin

2006

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Abstract. Near-Earth objects (NEOs) are objects of a special interest from the point of view not only of cosmogonic problems of the Solar system, but of the applied problems as well (the problem of asteroid hazard, NEOs as the potential sources of raw materials, etc.). They are much smaller in sizes than main-belt asteroids (MBAs), very irregular in shape and covered with a great number of craters of different sizes. Most of NEOs are covered by regolith of low thermal inertia and different thickness. Objects with complex non-principal axis rotation (tumbling bodies) and with super-fast rotational periods have been detected among them. The new data, based on photometric and radar observations, evidence that about 15 − 20 % of NEOs could be binary systems. Most of the classified NEOs fragments of differentiated assemblages of S-and Q-types. Analysis of physical properties of NEOs clearly indicates that the asteroid main-belt is the principal source of their origin and only about 10 % of NEOs have a cometary origin.

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The Rubble-Pile Asteroid Itokawa as Observed by Hayabusa

Cited by 859 publications

References 23 publications

Thermo-physical properties of 162173 (1999 JU3), a potential flyby and rendezvous target for interplanetary missions

Thermo-physical properties of 162173 (1999 JU3), a potential flyby and rendezvous target for interplanetary missions

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

Near-Earth objects as principal impactors of the Earth: Physical properties and sources of origin

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