An artificial impact on the asteroid (162173) Ryugu formed a crater in the gravity-dominated regime

Arakawa, Masahiko; Saiki, Takanao; Wada, Koji; Ogawa, Kazunori; Kadono, Toshihiko; Shirai, Kei; Sawada, Hirotaka; Ishibashi, Ko; Honda, Rie; Sakatani, Naoya; Iijima, Y.; Okamoto, Chisato; Yano, Hajime; Takagi, Y.; Hayakawa, Masahiko; Michel, Patrick; Jutzi, Martin; Shimaki, Y.; Kimura, Shinichi; Mimasu, Yuya; Toda, Tomoaki; Imamura, Hiroshi; Nakazawa, Shozo; Hayakawa, H.; Sugita, Seiji; Morota, T.; Kameda, Shingo; Tatsumi, Eri; Cho, Yuichiro; Yoshioka, Kazuo; Yokota, Yasuhiro; Matsuoka, Moe; Yamada, Manabu; Kouyama, T.; Honda, Chikatoshi; Tsuda, Yuichi; Watanabe, S.; Yoshikawa, Makoto; Tanaka, Satoshi; Terui, Fuyuto; Kikuchi, Shota; Yamaguchi, Tomohiro; Ogawa, Naoko; Ono, Go; Yoshikawa, K.; Takahashi, T.; Takei, Yuto; Fujii, Atsushi; Takeuchi, Hiroshi; Yamamoto, Yukio; Okada, T.; Hirose, Chikako; Hosoda, Saichi; Mori, Osamu; Shimada, Takanobu; Soldini, Stefania; Tsukizaki, Ryudo; Iwata, T.; Ozaki, Masanobu; Okazaki, Ryuji; Namiki, Noriyuki; Kitazato, K.; Tachibana, Shogo; Ikeda, Hitoshi; Hirata, Naru; Noguchi, Rina; Miura, Akira

doi:10.1126/science.aaz1701

Cited by 198 publications

(212 citation statements)

References 33 publications

(43 reference statements)

Supporting

Mentioning

196

Contrasting

Order By: Relevance

“…Seismic shaking may be a driver that induces granular convection. We note that seismic waves may be significantly attenuated in granular media in a microgravity environment [Yasui et al, 2015;Matsue et al, 2020], as seen by the Hayabusa2 SCI impact experiment [Arakawa et al, 2020, Nishiyama et al, 2020. Hypervelocity impact processes also resurface and reorganize the interior, depending on their energy levels [e.g., Wünnemann et al, 2006].…”

Section: Insights Into Reshaping and Top Shapes' Interiors From Surfamentioning

confidence: 56%

Spin-driven evolution of asteroids' top-shapes at fast and slow spins seen from (101955) Bennu and (162173) Ryugu

Hirabayashi

Nakano

Tatsumi

et al. 2020

Icarus

View full text Add to dashboard Cite

Proximity observations by OSIRIS-REx and Hayabusa2 provided clues on the shape evolution processes of the target asteroids, (101955) Bennu and (162173) Ryugu. Their oblate shapes with equatorial ridges, or the so-called top shapes, may have evolved due to their rotational conditions at present and in the past. Different shape evolution scenarios were previously proposed; Bennu's top shape may have been driven by surface processing, while Ryugu's may have been developed due to large deformation. These two scenarios seem to be inconsistent. Here, we revisit the structural analyses in earlier works and fill a gap to connect these explanations. We also apply a semi-analytical technique for computing the cohesive strength distribution in a uniformly rotating triaxial ellipsoid to characterize the global failure of top-shaped bodies. Assuming that the structure is uniform, our semi-analytical approach describes the spatial variations in failed regions at different spin periods; surface regions are the most sensitive at longer spin periods, while interiors fail structurally at shorter spin periods. This finding suggests that the shape evolution of a top shape may vary due to rotation and internal structure, which can explain the different evolution scenarios of Bennu's and Ryugu's top shapes. We interpret our results as the indications of top shapes' various evolution processes. Highlights • We reanalyzed results from FEM analyses for asteroids Bennu and Ryugu, the targets of OSIRIS-REx and Hayabusa2, respectively. • We also applied a semi-analytical approach to quantify how the failure modes of top shapes vary with spin. • Top shapes may evolve by two deformation modes: surface processing at low spin and internal failure at high spin.

show abstract

Section: Insights Into Reshaping and Top Shapes' Interiors From Surfamentioning

confidence: 56%

Spin-driven evolution of asteroids' top-shapes at fast and slow spins seen from (101955) Bennu and (162173) Ryugu

Hirabayashi

Nakano

Tatsumi

et al. 2020

Icarus

View full text Add to dashboard Cite

show abstract

“…Based on the Interplanetary Meteoroid Environment Model 2 by Soja et al (2019), the mean impact speed of a 250 µm dust particle in a near Earth orbit is approximately 16 km/s and has an flux of ∼8•10 −9 −2 −1 . Assuming that the rock imaged by MasCam has been exposed at the surface since Ryugu's formation (approximately 10 7 years ago (Arakawa et al 2020)), this flux results in about 1.6•10 5 accumulated impacts in the imaged 25 cm × 25 cm scene or 250 impacts per cm 2 . This implies that the total area affected by an impact of this size is approximately 10 times larger than the area of the scene meaning that the surface should show traces of such impact cater features and that micrometeoroid bombardment plays a role in the formation of Ryugu's surface roughness.…”

Section: Roughness Caused By Micrometeoroid Impactsmentioning

confidence: 99%

Surface roughness of asteroid (162173) Ryugu and comet 67P/Churyumov–Gerasimenko inferred fromin situobservations

Otto

Matz

Schröder

et al. 2020

Monthly Notices of the Royal Astronomical Society

View full text Add to dashboard Cite

Alteration processes on asteroid and comet surfaces, such as thermal fracturing, (micrometeorite) impacts or volatile outgassing, are complex mechanisms that form diverse surface morphologies and roughness on various scales. These mechanisms and their interaction may differ on the surfaces of different bodies. Asteroid Ryugu and comet 67P/Churyumov-Gerasimenko, both, have been visited by landers which imaged the surfaces in high spatial resolution. We investigate the surface morphology and roughness of Ryugu and 67P/Churyumov-Gerasimenko based on high resolution in situ images of 0.2 mm and 0.8 mm pixel resolution over an approximately 25 cm and 80 cm wide scene, respectively. To maintain comparability and reproducibility, we introduce a method to extract surface roughness descriptors (fractal dimension, Hurst exponent, joint roughness coefficient, root mean square slope, hemispherical crater density, small scale roughness parameter and Hapke mean slope angle) from in situ planetary images illuminated by LEDs. We validate our method and choose adequate parameters for an analysis of the roughness of the surfaces. We also derive the roughness descriptors from 3-dimensional shape models of Ryugu and orbiter camera images and show that the higher spatially resolved images results in a higher roughness. We find that 67P/Churyumov-Gerasimenko is up to 6% rougher than Ryugu depending on the descriptor used and attribute this difference to the different intrinsic properties of the materials imaged and the erosive processes altering them. On 67P/Churyumov-Gerasimenko sublimation appears to be the main cause for roughness, while on Ryugu micrometeoroid bombardment as well as thermal fatigue and solar weathering may play a significant role in shaping the surface.

show abstract

“…On asteroids, regolith production by the break-up of boulders due to micrometeoroid impacts is frustrated by the low escape velocities from these bodies compared to typical ejecta speed produced by hypervelocity impacts (Housen et al 1979;Housen & Holsapple 2011), although the observation of the ejecta cloud from the impact of the Hayabusa2 Small Carry-on Impactor on Ryugu showed that low-speed ejecta can be produced and fall back on a small asteroid surface (Arakawa et al 2020). It is also likely that micrometeoroid impacts are able to kick out boulders of a few decimeters in size from small asteroid surfaces: this process has been suggested among others for the activity observed by the OSIRIS-REx mission on the asteroid Bennu (Lauretta et al 2019).…”

Section: Introductionmentioning

confidence: 99%

Network of thermal cracks in meteorites due to temperature variations: new experimental evidence and implications for asteroid surfaces

Libourel

Ganino

Delbò

et al. 2020

Monthly Notices of the Royal Astronomical Society

View full text Add to dashboard Cite

In recent years several studies have shown the importance of thermal fracturing of rocks due to temperature variations, on Earth and Mars. Rock thermal cracking might also be a process at play on the lunar surface. These temperature variations as well as change rates can reach important amplitude on bodies without an atmosphere, in particular on those that reach small perihelion distances such as near-Earth asteroids. On the other hand, the formation, geometry and extension of cracks on these bodies have not been fully investigated yet. Here we show results of thermal cracking laboratory experiments on chondrite meteorites, which develop networks of cracks when subjected to rapid temperature cycles with amplitudes similar to those experienced by asteroids with low perihelion distances. The depth of the cracks can reach a few hundred of microns in some hundreds of temperature cycles, in agreement with theoretical studies. We find that dehydration of hydrous minerals enhances the cracking process. The formation of crack networks increases the porosity both at the surface and in the sub-surface of our specimens. We propose that this process could help explaining the recent finding of the very highly porous surfaces of most of the boulders on the asteroids Ryugu and Bennu.

show abstract

An artificial impact on the asteroid (162173) Ryugu formed a crater in the gravity-dominated regime

Cited by 198 publications

References 33 publications

Spin-driven evolution of asteroids' top-shapes at fast and slow spins seen from (101955) Bennu and (162173) Ryugu

Spin-driven evolution of asteroids' top-shapes at fast and slow spins seen from (101955) Bennu and (162173) Ryugu

Surface roughness of asteroid (162173) Ryugu and comet 67P/Churyumov–Gerasimenko inferred fromin situobservations

Network of thermal cracks in meteorites due to temperature variations: new experimental evidence and implications for asteroid surfaces

Contact Info

Product

Resources

About