Simulation of Seismic Wave Propagation on Asteroid Ryugu Induced by The Impact Experiment of The Hayabusa2 Mission: Limited Mass Transport by Low Yield Strength of Porous Regolith

Nishiyama, Gaku; Kawamura, Taïchi; Namiki, Noriyuki; Fernando, Benjamin; Leng, Kuangdai; Onodera, Keisuke; Sugita, Seiji; Saiki, Takanao; Imamura, Hiroshi; Takagi, Y.; Yano, Hajime; Hayakawa, Masahiko; Okamoto, Chisato; Sawada, Hirotaka; Tsuda, Yuichi; Ogawa, Kazunori; Nakazawa, Shozo; Iijima, Y.

doi:10.1029/2020je006594

Cited by 16 publications

(13 citation statements)

References 60 publications

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“…Nevertheless, the latter Kibidango‐forming impact did not significantly destroy the morphology of predated Momotaro. This observation suggests a low seismic efficiency (i.e., the conversion ratio of impactor's kinetic energy to seismic energy) on Ryugu, which is consistent with the artificial impact experiment by SCI (Arakawa et al., 2020; Nishiyama et al., 2020). These craters are particularly rich in boulders and this could reflect the subsurface structure of this region and/or crater formation process.…”

Section: Crater Morphological Observationsupporting

confidence: 82%

“…Regolith convection is thought to be activated by seismic shaking (Yamada et al., 2016). Though the SCI experiment revealed low seismic efficiency at least for the impact that formed a 15 m crater (Arakawa et al., 2020; Nishiyama et al., 2020), the seismic energy deposited by a large‐scale impact that would form a >100‐m crater, needs to be evaluated. If granular convection takes place on Ryugu, this process would sort the size of particles because small particles can travel much more easily while larger rocks remain at the surface.…”

Section: Crater Morphological Observationmentioning

confidence: 99%

“…The apparent lack of craters around Urashima as compared to the Kolobok area (Figure 1) is consistent with this interpretation. Although the seismic efficiency on Ryugu was found low by the artificial impact experiment, the seismic shaking due to the Urashima‐forming impact could also have degraded a number of craters nearby because the seismic energy with this 290‐m crater formation is still high enough to induce acceleration greater than the gravity (Nishiyama et al., 2020). This hypothesis is also consistent with the fact that the CSFD for the eastern hemisphere does not show the transition of the isochron if constructed with the data from SCI crater‐search campaign, whereas the CSFD from the global observation campaign does.…”

Section: Crater Chronology Of Ryugumentioning

confidence: 99%

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Geologic History and Crater Morphology of Asteroid (162173) Ryugu

et al. 2021

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Crater morphology and surface age of asteroid (162173) Ryugu are characterized using the high‐resolution images obtained by the Hayabusa2 spacecraft. Our observations reveal that the abundant boulders on and under the surface of the rubble‐pile asteroid affect crater morphology. Most of the craters on Ryugu exhibit well‐defined circular depressions, unlike those observed on asteroid Itokawa. The craters are typically outlined by boulders remaining on the rim. Large craters (diameter > 100 m) host abundant and sometimes unproportionally large boulders on their floors. Small craters (<20 m) are characterized by smooth circular floors distinguishable from the boulder‐rich exterior. Such small craters tend to have dark centers of unclear origin. The correlation between crater size and boulder number density suggests that some processes sort the size of boulders in the shallow (<30 m) subsurface. Furthermore, the crater size‐frequency distributions (CSFDs) of different regions on Ryugu record multiple geologic events, revealing the diverse geologic history on this 1‐km asteroid. Our crater‐counting analyses indicate that the equatorial ridge is the oldest structure of Ryugu and was formed 23–30 Myr ago. Then, Ryugu was partially resurfaced, possibly by the impact that formed the Urashima crater 5–12 Myr ago. Subsequently, a large‐scale resurfacing event formed the western bulge and the fossae 2–9 Myr ago. Following this process, the spin of Ryugu slowed down plausibly due to the YORP effect. The transition of isochrons in a CSFD suggests that Ryugu was decoupled from the main belt and transferred to a near‐Earth orbit 0.2–7 Myr ago.

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Section: Crater Morphological Observationsupporting

confidence: 82%

Section: Crater Morphological Observationmentioning

confidence: 99%

Section: Crater Chronology Of Ryugumentioning

confidence: 99%

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Geologic History and Crater Morphology of Asteroid (162173) Ryugu

et al. 2021

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“…The migration of regolith materials on asteroids is possible to be initiated by some disturbance factors, including but not limited to global change of the surface dynamical environment due to varying spin state [15], and exogenous excitation, such as impact events which could give rise to stress waves and seismic shaking [16,17]. A slow mechanism that can modify the spin rates and obliquities of small bodies by thermal radiation forces and torques, referred to as Yarkovsky-O'Keefe-Radzievskii-Paddack (YORP) effect [18], plays an important role in driving the surface evolution process of small bodies.…”

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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“…The migration of regolith materials on asteroids is possible to be initiated by some disturbance factors, including but not limited to global change of the surface dynamical environment due to varying spin state [15], and exogenous excitation, such as impact events which could give rise to stress waves and seismic shaking [16,17]. A slow mechanism that can modify the spin rates and obliquities of small bodies by thermal radiation forces and torques in the space environment, referred to as Yarkovsky-O'Keefe-Radzievskii-Paddack (YORP) effect [18], plays an important role in driving the surface evolution process of small bodies.…”

Section: Introductionmentioning

confidence: 99%

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

Huang¹,

Yu²,

Cheng³

et al. 2021

Preprint

View full text Add to dashboard Cite

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-slidingshedding 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 largescale trajectories of the system are calculated to clarify the dynamical characteristics of long-term regolith movement. Generally, we find 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 evo-

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Simulation of Seismic Wave Propagation on Asteroid Ryugu Induced by The Impact Experiment of The Hayabusa2 Mission: Limited Mass Transport by Low Yield Strength of Porous Regolith

Cited by 16 publications

References 60 publications

Geologic History and Crater Morphology of Asteroid (162173) Ryugu

Geologic History and Crater Morphology of Asteroid (162173) Ryugu

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

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

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