Crater depth-to-diameter ratios on asteroid 162173 Ryugu d/D of craters on Ryugu

Noguchi, Rina; Hirata, Naoyuki; Hirata, Naru; Shimaki, Yuri; Nishikawa, Naoki; Tanaka, Sayuri; Sugiyama, Takaaki; Morota, Tomokatsu; Sugita, Seiji; Cho, Yuichiro; Honda, Rie; Kameda, Shingo; Tatsumi, Eri; Yoshioka, Kazuo; Sawada, Hirotaka; Yokota, Yasuhiro; Sakatani, Naoya; Hayakawa, Masahiko; Matsuoka, Moe; Yamada, Manabu; Kouyama, Toru; Suzuki, Hidehiko; Honda, Chikatoshi; Ogawa, Kazunori; Kanamaru, Masanori; Watanabe, Sei-ichiro
Bibliographical reference

Icarus

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1
2021
Journal
Number of authors
26
IAC number of authors
1
Citations
7
Refereed citations
7
Description
The near-Earth asteroid 162173 Ryugu, the target of the Hayabusa2 mission, is noted to be a spinning top-shaped rubble-pile. Craters are among the most prominent surface features on Ryugu. Their shapes, particularly their depth-to-diameter ratio (d/D), can provide an important proxy for probing both the internal structure and surface processes of planetary bodies. Here, we report d/D of every impact crater on Ryugu using a shape model derived from stereo-photoclinometry. We found that the average, standard deviation, and observed range of d/D for the entire set of craters are 0.09, 0.02, and 0.03-0.15, respectively. Except for possible pit craters, the maximum d/D of large craters on Ryugu (D > 50 m) is close to 0.13, which is comparable with those of fresh simple craters on rocky asteroids, such as Gaspra and Ida. Conversely, the d/D of small craters (D < 50 m) increases with the crater diameter. This behavior implies that a smaller crater on Ryugu is formed as a shallower crater. As on Itokawa, the surface environment on Ryugu likely inhibits craters becoming deep. This especially affects smaller craters, as their normal small depth decreases in the Ryugu environment and they become still more shallow. As a result, small craters rapidly degrade beyond the point where they can be identified as candidate craters. This is likely responsible for the apparent lack of small craters. The d/D has no reliable relationship with the types of crater classification in Hirata et al. (2020). Examination of latitudinal and longitudinal variation in d/D of craters on Ryugu revealed no statistically significant trends.
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Minor Bodies of the Solar System
This project studies the physical and compositional properties of the so-called minor bodies of the Solar System, that includes asteroids, icy objects, and comets. Of special interest are the trans-neptunian objects (TNOs), including those considered the most distant objects detected so far (Extreme-TNOs or ETNOs); the comets and the comet-asteroid
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