Rotational states and shapes of Ryugu and Bennu: Implications for interior structure and strength

Roberts, J. H.; Barnouin, O. S.; Daly, M. G.; Walsh, K. J.; Nolan, M. C.; Daly, R. T.; Michel, Patrick; Zhang, Yun; Perry, M. E.; Neumann, Gregory A.; Seabrook, J. A.; Gaskell, R. W.; Palmer, E. E.; Weirich, J. R.; Watanabe, Sei‐ichiro; Hirata, Naoyuki; Sugita, Seiji; Scheeres, Daniel J.; McMahon, Jay W.; Лауретта, Д. С.

doi:10.1016/j.pss.2021.105268

Cited by 18 publications

(17 citation statements)

References 44 publications

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“…Observations by OCAMS and OLA have enabled the construction of highresolution global digital terrain models (GDTMs; Barnouin et al 2020) of the asteroid with ground sample distances (GSDs) of 0.2 m. These GDTMs reveal that Bennu is a topshaped, rubble-pile asteroid (Barnouin et al 2019;Daly et al 2020a), made from reaccumulated fragments of a larger parent body that was catastrophically disrupted (Michel et al 2020). Bennu possesses broad north-south longitudinal ridges that extend in some instances across nearly all latitudes of the asteroid; although these ridges are muted and can be difficult to discern, they are evident in spherical harmonic analyses, both global and hemispherical, of the shape of Bennu (Barnouin et al 2019;Daly et al 2020a;Roberts et al 2021). These ridges explain the diamond shape of Bennu that becomes apparent when the asteroid is viewed from the poles (Barnouin et al 2019).…”

Section: Introductionmentioning

confidence: 90%

“…Hokioi crater is located between two broad longitudinal ridges that span most of the asteroid's length from the north to the south pole (Barnouin et al 2019;Daly et al 2020a;Roberts et al 2021). These ridges are located near 0°and 90°E longitude (Figure 1(a)) and stand slightly above the rest of the asteroid (Barnouin et al 2019;Daly et al 2020a).…”

Section: Global Context Of the Nightingale Sitementioning

confidence: 99%

“…Bennu shows evidence for internal stiffness (Barnouin et al 2019). Its shape can be sustained by friction angles of <18°T (Barnouin et al 2019;Roberts et al 2021), or bulk cohesion of ∼1 Pa (Scheeres et al 2019;Roberts et al 2021). The density of Bennu is heterogeneous, with lower densities at its center and along its equatorial bulge (Scheeres et al 2019).…”

Section: Introductionmentioning

confidence: 99%

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Geologic Context of the OSIRIS-REx Sample Site from High-resolution Topography and Imaging

Barnouin¹,

Jawin²,

Daly³

et al. 2022

Planet. Sci. J.

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The OSIRIS-REx spacecraft collected a surface sample from Hokioi crater (55.8° N, 42.3° E; diameter ∼20 m) on the asteroid Bennu in 2020 October. We explore the geology of the sample collection site, known as Nightingale, by using digital terrain models, relative albedo maps, and images collected by the OSIRIS-REx spacecraft. Hokioi crater sits at the northwest edge of an older, larger (120 m diameter) crater between two north–south ridges respectively located at roughly 0° and 90° longitude, between which unconsolidated material generally migrates from the geopotential high at the north (+Z) pole to the geopotential low at the equator. The impact that formed Hokioi crater exposed relatively unweathered, fine-grained dark material that we observe within and ejected beyond the crater. The regional slope and steep crater walls to the north of the Nightingale site have enabled a mix of the dark debris and brighter material (which may include carbonates and/or exogenic basalts) surrounding Hokioi crater to migrate onto the crater floor, where the sample was collected; some of this material may be old ejecta excavated from up to 10 m depth when the 120 m diameter crater formed. We therefore expect the OSIRIS-REx sample to include materials of varying brightnesses, compositions, and exposure ages, derived primarily from the 0°–90° longitude quadrant and from as deep as 10 m. The sample may also include material derived from the impactor that formed Hokioi crater. We expect it to have low cohesion (≪0.6 Pa) and a friction angle between 32° and 39°.

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Section: Introductionmentioning

confidence: 90%

Section: Global Context Of the Nightingale Sitementioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Geologic Context of the OSIRIS-REx Sample Site from High-resolution Topography and Imaging

Barnouin¹,

Jawin²,

Daly³

et al. 2022

Planet. Sci. J.

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“…We also explore the effects of cohesion, c . Recall that a global cohesion value of c = 1 Pa is sufficient to form the equatorial ridge of Bennu (Roberts et al., 2021; Scheeres et al., 2019). As a endmember case (Figure 8), we use c = 1 Pa with the plausible ϕ = 40° and T = 3 m. This thickness is derived from the depths of mounds at the centers of three craters on Bennu (R. T. Daly et al., 2020), which offer one direct measure of the approximate depth of the unconsolidated surface layer (Quaide & Oberbeck, 1968).…”

Section: Slope Stability Analysismentioning

confidence: 99%

The Formation of Terraces on Asteroid (101955) Bennu

et al. 2022

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“…Recent work has shown that typical cohesive strengths of small bodies (<1 km in diameter) are likely around a few hundred Pa . Recent investigations of asteroids (101955) Bennu and (162173) Ryugu by OSIRIS-REx (Barnouin et al 2019) and Hayabusa2 (Watanabe et al 2019;Roberts et al 2021), respectively, showed very low cohesive strengths on their surfaces (less than ∼10 Pa), although no upper bounds of the bulk cohesive strength were provided.…”

Section: Introductionmentioning

confidence: 99%

Active Main-belt Asteroid (6478) Gault: Constraint on Its Cohesive Strength and the Fate of Ejected Particles in the Solar System

Nakano¹,

Kim²,

Hirabayashi³

2022

Planet. Sci. J.

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Active asteroid (6478) Gault sheds mass independent of location along its orbit. Rotational instability is considered to induce the observed activities. If this is the case, because Gault’s breakup event has not been detected, surface failure is likely, implying that its surface materials are constantly ejected while its major body remains intact. Given this scenario, we first constrain Gault’s bulk cohesive strength. We then characterize heliocentric trajectories of ejected particles over thousands of years. The results show that Gault may be sensitive to structural failure at the current spin period (∼2.5 hr). Gault’s bulk density needs to be below 1.75 g cm−3 in order for particles on the equatorial surface to be shed owing to centrifugal forces. In this case, Gault requires cohesive strength of at least ∼200 Pa to maintain the structure at the center, whereas the surface strength needs to be less than ∼100 Pa to induce mass shedding. This suggests that Gault’s structure may consist of a weak surface layer atop a strong core. The trajectories of dust ejected from Gault depend on how efficiently they are accelerated by solar radiation pressure. Escaped particle clouds with sizes of < ∼100 μm could collide with Gault after ∼700–5300 yr with speeds of ∼0.2 km s−1. This implies a temporal increase in the impact flux and complex interactions between the ejected particles and their host body.

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Rotational states and shapes of Ryugu and Bennu: Implications for interior structure and strength

Cited by 18 publications

References 44 publications

Geologic Context of the OSIRIS-REx Sample Site from High-resolution Topography and Imaging

Geologic Context of the OSIRIS-REx Sample Site from High-resolution Topography and Imaging

The Formation of Terraces on Asteroid (101955) Bennu

Active Main-belt Asteroid (6478) Gault: Constraint on Its Cohesive Strength and the Fate of Ejected Particles in the Solar System

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