Shape model and surface properties of the OSIRIS-REx target Asteroid (101955) Bennu from radar and lightcurve observations

Nolan, M. C.; Magri, C.; Howell, E. S.; Benner, L. A. M.; Giorgini, Jon D.; Hergenrother, C. W.; Hudson, R. S.; Лауретта, Д. С.; Margot, Jean-Luc; Ostro, S. J.; Scheeres, Daniel J.

doi:10.1016/j.icarus.2013.05.028

Cited by 206 publications

(229 citation statements)

References 28 publications

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“…Also, instead of using the visual lightcurves first, we started by using the thermal measurements. This approach worked very well in the case of (101955) Bennu where the radiometrically established spin-axis orientation ) agreed within error bars with the radar derived value (Nolan et al 2013). Furthermore, in the case of the very elongated object (25143) Itokawa, a careful analysis of thermal data in combination with a spherical shape model led to realistic predictions for the orientation of the object's spin vector within approximately 10…”

Section: Spherical Shape Modelsupporting

confidence: 58%

Hayabusa-2 mission target asteroid 162173 Ryugu (1999 JU₃): Searching for the object’s spin-axis orientation

Müller

Ďurech

Ishiguro

et al. 2017

A&A

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The JAXA Hayabusa-2 mission was approved in 2010 and launched on December 3, 2014. The spacecraft will arrive at the nearEarth asteroid 162173 Ryugu (1999 JU 3 ) in 2018 where it will perform a survey, land and obtain surface material, then depart in December 2019 and return to Earth in December 2020. We observed Ryugu with the Herschel Space Observatory in April 2012 at far-infrared thermal wavelengths, supported by several ground-based observations to obtain optical lightcurves. We reanalysed previously published Subaru-COMICS and AKARI-IRC observations and merged them with a Spitzer-IRS data set. In addition, we used a large set of Spitzer-IRAC observations obtained in the period January to May, 2013. The data set includes two complete rotational lightcurves and a series of ten "point-and-shoot" observations, all at 3.6 and 4.5 µm. The almost spherical shape of the target together with the insufficient lightcurve quality forced us to combine radiometric and lightcurve inversion techniques in different ways to find the object's spin-axis orientation, its shape and to improve the quality of the key physical and thermal parameters. Handling thermal data in inversion techniques remains challenging: thermal inertia, roughness or local structures influence the temperature distribution on the surface. The constraints for size, spin or thermal properties therefore heavily depend on the wavelengths of the observations. We find that the solution which best matches our data sets leads to this C class asteroid having a retrograde rotation with a spin-axis orientation of (λ = 310• -340• ) in ecliptic coordinates, an effective diameter (of an equal-volume sphere) of 850 to 880 m, a geometric albedo of 0.044 to 0.050 and a thermal inertia in the range 150 to 300 J m −2 s −0.5 K −1 . Based on estimated thermal conductivities of the top-layer surface in the range 0.1 to 0.6 W K −1 m −1 , we calculated that the grain sizes are approximately equal to between 1 and 10 mm. The finely constrained values for this asteroid serve as a 'design reference model', which is currently used for various planning, operational and modelling purposes by the Hayabusa2 team.

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Section: Spherical Shape Modelsupporting

confidence: 58%

Hayabusa-2 mission target asteroid 162173 Ryugu (1999 JU₃): Searching for the object’s spin-axis orientation

Müller

Ďurech

Ishiguro

et al. 2017

A&A

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“…We scaled this shape to mean dimensions of 1 Â 0.33 Â 0.33 km to represent a small Near-Earth Asteroid (NEA) and to 21 Â 7 Â 7 km to represent a comet. The 0.5-km mean diameter of the model asteroid is close to that of the OSIRIS-Rex mission target, 101955 Bennu (Nolan et al, 2013), whereas the comet's 10-km mean diameter is comparable to 1P/Halley and 10P/Tempel 2.…”

Section: Target Bodiessupporting

confidence: 50%

Radio reflection imaging of asteroid and comet interiors II: Results and recommendations

Grimm

Stillman

Sava

et al. 2015

Advances in Space Research

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“…Previous thermophysical modelling of thermal-infrared observations of Itokawa indicate that the surface is rough at these spatial scales but the distribution is unknown (Müller et al 2005). Radar circular polarisation ratios also give an indication of an asteroid's wavelength-scale roughness (Ostro et al 2002;Benner et al 2008), and Itokawa's disk-integrated ratio at 3.5 cm, µ C = 0.47 ± 0.04, is significantly larger than that at 12.6 cm, µ C = 0.26 ± 0.04 (Ostro et al 2004;Nolan et al 2013). This indicates that most of the surface roughness occurs at the cm-scale, and won't effectively be described in the highest resolution shape model of Itokawa (∼3 million facets) as it has a facet size of 0.5 m .…”

Section: Thermophysical Analysis and Measured Density Inhomogeneitymentioning

confidence: 99%

The internal structure of asteroid (25143) Itokawa as revealed by detection of YORP spin-up

Lowry

Weissman

Duddy

et al. 2014

A&A

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Context. Near-Earth asteroid (25143) Itokawa was visited by the Hayabusa spacecraft in 2005, resulting in a highly detailed shape and surface topography model. This model has led to several predictions for the expected radiative torques on this asteroid, suggesting that its spin rate should be decelerating. Aims. To detect changes in rotation rate that may be due to YORP-induced radiative torques, which in turn may be used to investigate the interior structure of the asteroid. Methods. Through an observational survey spanning 2001 to 2013 we obtained rotational lightcurve data at various times over the last five close Earth-approaches of the asteroid. We applied a polyhedron-shape-modelling technique to assess the spin-state of the asteroid and its long term evolution. We also applied a detailed thermophysical analysis to the shape model determined from the Hayabusa spacecraft. Results. We have successfully measured an acceleration in Itokawa's spin rate of dω/dt = (3.54 ± 0.38) × 10 −8 rad day −2 , equivalent to a decrease of its rotation period of ∼45 ms year −1 . From the thermophysical analysis we find that the centre-of-mass for Itokawa must be shifted by ∼21 m along the long-axis of the asteroid to reconcile the observed YORP strength with theory. Conclusions. This can be explained if Itokawa is composed of two separate bodies with very different bulk densities of 1750 ± 110 kg m −3 and 2850 ± 500 kg m −3 , and was formed from the merger of two separate bodies, either in the aftermath of a catastrophic disruption of a larger differentiated body, or from the collapse of a binary system. We therefore demonstrate that an observational measurement of radiative torques, when combined with a detailed shape model, can provide insight into the interior structure of an asteroid. Futhermore, this is the first measurement of density inhomogeneity within an asteroidal body, that reveals significant internal structure variation. A specialised spacecraft is normally required for this.

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Shape model and surface properties of the OSIRIS-REx target Asteroid (101955) Bennu from radar and lightcurve observations

Cited by 206 publications

References 28 publications

Hayabusa-2 mission target asteroid 162173 Ryugu (1999 JU₃): Searching for the object’s spin-axis orientation

Hayabusa-2 mission target asteroid 162173 Ryugu (1999 JU₃): Searching for the object’s spin-axis orientation

Radio reflection imaging of asteroid and comet interiors II: Results and recommendations

The internal structure of asteroid (25143) Itokawa as revealed by detection of YORP spin-up

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Shape model and surface properties of the OSIRIS-REx target Asteroid (101955) Bennu from radar and lightcurve observations

Cited by 206 publications

References 28 publications

Hayabusa-2 mission target asteroid 162173 Ryugu (1999 JU3): Searching for the object’s spin-axis orientation

Hayabusa-2 mission target asteroid 162173 Ryugu (1999 JU3): Searching for the object’s spin-axis orientation

Radio reflection imaging of asteroid and comet interiors II: Results and recommendations

The internal structure of asteroid (25143) Itokawa as revealed by detection of YORP spin-up

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Product

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Hayabusa-2 mission target asteroid 162173 Ryugu (1999 JU₃): Searching for the object’s spin-axis orientation

Hayabusa-2 mission target asteroid 162173 Ryugu (1999 JU₃): Searching for the object’s spin-axis orientation