Reconstructing the formation history of top-shaped asteroids from the surface boulder distribution

Cheng, Bin Kang; Yu, Yang; Asphaug, Erik; Michel, Patrick; Richardson, D. C.; Hirabayashi, Masatoshi; Yoshikawa, Makoto; Baoyin, Hexi

doi:10.1038/s41550-020-01226-7

Cited by 34 publications

(28 citation statements)

References 31 publications

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“…At the surface region, when the interparticle friction and cohesion cannot counteract the increasing surface slopes owing to changes in the spin state of the body, local landslides would occur in this region and, thus, the regional morphology is modified. With a given friction angle, to sustain surface stability with increasing spins, a spherical body would evolve to an oblate shape with a raised equatorial bulge via surface landslides [190,191]. This kind of shape is often referred to as a "top" shape, as it resembles the spinning top toy.…”

Section: Spin-driven Structural Evolutionmentioning

confidence: 99%

Shapes, structures, and evolution of small bodies

Yun

Michel

2021

Astrodyn

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Small bodies are among the best tracers of our Solar System's history. A large number of space missions to small bodies (past and future) offer a unique opportunity to use these bodies as a natural laboratory to study the different processes, mechanical structures, and responses that drive the origin and evolution of small bodies, which are connected to the origin, evolution, and current architecture of the Solar System. Images of small bodies sent by spacecraft have revealed unexpectedly rich and complex geological worlds.In addition to very diverse compositions, small bodies in the Solar System have highly diverse shapes and structures, which reflect both different evolutionary paths and material properties. Furthermore, each individual body has diverse geological features on its surface, which include craters of various sizes and depths, boulders of different sizes and morphologies, lineaments, fractures, pits, signatures of landslides, terraces, and ridges. Such a geological richness could not be detected via ground-based observations, and we are still at the beginning of understanding their significance on the low-gravity surfaces on which they manifest. The combination of space mission data and numerical modeling allows us to enrich our understanding of the origin, evolution, and physical properties of these fascinating bodies. For instance, starting from the shape models, bulk densities, and spin rates determined from space mission data, we can investigate the formation mechanisms that lead to the observed properties of small bodies. We can also infer the interior and mechanical properties (e.g., friction and cohesion) that allow a small body to be structurally stable, as well as its further potential evolution under processes such as a spin rate increase or an impact. Then, considering the various processes that these bodies experience during their evolution, we can investigate how these processes modify their properties and, in turn, how those properties influence the outcome of these processes. This paper reviews our current knowledge of small-body shapes and structures and discusses the various processes that are responsible for their formation and evolution, which can modify the characteristics of the bodies. We separately consider each population of small bodies, although in some cases, such as active asteroids and comets, the distinction between two populations solely in terms of physical properties is not clear. We then summarize the main findings regarding the physical properties of small bodies that have been the target of rendezvous or sample return missions.

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Section: Spin-driven Structural Evolutionmentioning

confidence: 99%

Shapes, structures, and evolution of small bodies

Yun

Michel

2021

Astrodyn

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“…These regolith layer activities highly depend on the dynamical environments near the surfaces of the asteroids, which are largely governed by the complicated geometries of the bodies and their irregular gravitational fields. Recent studies show the global patterns of the mass movements can decipher the surface evolutionary process and contribute to as-sessing the surface mechanical properties of small bodies [12,13,14].…”

Section: Introductionmentioning

confidence: 99%

“…They derived the criteria of coexistence and transformation of static and flowing regolith regimes. Cheng et al [12] simulated the regolith migration driven by YORP spin-up employing discrete element method and observed that creeping granular materials moved from mid-high latitudes toward low latitudes and formed a pronounced equatorial bulge. Jawin et al [4] documented evidence of global patterns of mass movement on the surface of Bennu based on plenty of highresolution images taken by OSIRIS-REx cameras, unraveling the surface modification subject to regolith transport.…”

Section: Introductionmentioning

confidence: 99%

Long-term Trends of Regolith Movement on the Surface of Small Bodies

Huang

Cheng

et al. 2022

Preprint

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This paper studies the long-term migration of disturbed regolith materials on the surface of Solar System small bodies from the viewpoint of nonlinear dynamics. We propose an approximation model for secular mass movement, which combines the complex topography and irregular gravitational field. Choosing asteroid 101955 Bennu as a representative, the global change of the dynamical environment is examined, which presents a division of the creeping-sliding-shedding regions for a spun-up asteroid. In the creeping region, the dynamical equation of disturbed regolith grains is established based on the assumption of "trigger-slide" motion mode. The equilibrium points, local manifolds and large-scale trajectories of the system are calculated to clarify the dynamical characteristics of long-term regolith movement. Generally, we find that for a low spin rate, the surface regolith grains flow toward the middle latitudes from the polar/equatorial regions, which is dominated by the gradient of the geopotential. While spun up to a high rate, regolith grains tend to migrate toward the equator, which happens in parallel with a topological shift of the local equilibria at low latitudes. From a long-term perspective, we find the equilibrium points dominate the global trends of regolith movements. Using the methodology developed in this paper, we give a prospect or retrospect to the secular motion of regolith materials during the spin-up process, and the results reveal a significant regulatory role of the equilibria. Through a detailed look at the dynamical scheme under different spin rates, we achieve a macro forecast of the global trends of regolith motion during the spin-up process, which explains the global geologic evolution driven by the long-term movements of regolith materials.

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“…As examples of the latter microgravity regime, indeed the surfaces of both (101955) Bennu (Barnouin et al 2019) and (162173) Ryugu (Watanabe et al 2019) have been shown to be composed of loosely bound rubble. Many questions regarding the formation (Michel et al 2020;Cheng et al 2021), surface features (Shinbrot et al 2017;Bogdan et al 2020) and mechanical stability (Scheeres et al 2010;Sánchez & Scheeres 2020) of these asteroids still remain open.…”

Section: Introductionmentioning

confidence: 99%

Stick-slip Dynamics in Penetration Experiments on Simulated Regolith

Featherstone¹,

Bullard²,

Emm³

et al. 2021

Planet. Sci. J.

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The surfaces of many planetary bodies, including asteroids and small moons, are covered with dust to pebble-sized regolith held weakly to the surface by gravity and contact forces. Understanding the reaction of regolith to an external perturbation will allow for instruments, including sensors and anchoring mechanisms for use on such surfaces, to implement optimized design principles. We analyze the behavior of a flexible probe inserted into loose regolith simulant as a function of probe speed and ambient gravitational acceleration to explore the relevant dynamics. The EMPANADA experiment (Ejecta-Minimizing Protocols for Applications Needing Anchoring or Digging on Asteroids) flew on several parabolic flights. It employs a classic granular physics technique, photoelasticity, to quantify the dynamics of a flexible probe during its insertion into a system of bi-disperse, centimeter-sized model grains. We identify the force chain structure throughout the system during probe insertion at a variety of speeds and for four different levels of gravity: terrestrial, Martian, lunar, and microgravity. We identify discrete, stick-slip failure events that increase in frequency as a function of the gravitational acceleration. In microgravity environments, stick-slip behaviors are negligible, and we find that faster probe insertion can suppress stick-slip behaviors where they are present. We conclude that the mechanical response of regolith on rubble-pile asteroids is likely quite distinct from that found on larger planetary objects, and scaling terrestrial experiments to microgravity conditions may not capture the full physical dynamics.

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Reconstructing the formation history of top-shaped asteroids from the surface boulder distribution

Cited by 34 publications

References 31 publications

Shapes, structures, and evolution of small bodies

Shapes, structures, and evolution of small bodies

Long-term Trends of Regolith Movement on the Surface of Small Bodies

Stick-slip Dynamics in Penetration Experiments on Simulated Regolith

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