MISIP-2024 Project-6 – Understanding Planetary Surfaces: A Remote Sensing andLaboratory-based Approach for Future Mission Planning
Aditya Ray 1* , Lisa Vincent 2 *1Presidency University, 86/1 College Street, Kolkata, 700073, West Bengal, India

2

Utrecht University, Heidelberglaan 8, 3584 CS Utrecht, Netherlands* Equal contribution
162173 Ryugu is a spinning top Cb-type carbonaceous asteroid explored by the Hayabusa2 spacecraft(Sugita et al., 2019). The low bulk density (1,190 ± 20 kg m−3) and boulder-dominated surface indicate
it as a rubble-pile body having accumulated impact fragments (Watanabe et al., 2019). The publishedgeological map of Ryugu lacks significant detail. This study presents one of the most detailed
geomorphological maps of Ryugu to understand its geological evolution by investigating its formation,
impact history, surface composition. Previous studies based on Hayabusa2 ONC images (Michikami etal., 2019), obtained during the first month after the spacecraft's arrival in June 2018, were only able toproduce a coarse resolution map, considering just one-tenth of the boulder distribution (Sugita et al.,2019; Michikami et al., 2019) .
In this study, both 2018 and 2019 ONC images, processed Digital Elevation Model (DEM), and thermal
images obtained from Hayabusa2 were considered for mapping. The highest resolution data had a pixel
scale of approximately 0.25m (Ho et al., 2021). Forty-one craters with high confidence, 142 potential
craters with moderate confidence, and six circular features that are potentially large old craters wereidentified. Low-lying areas were identified as well as the equatorial ridge. The western bulge wasidentified from the DEM based on the elevation differences with the surrounding troughs, and thencompared with the previous work. This comparison shows that the western bulge, relative to the rest ofRyugu, exhibits deviations in crater diversity, spectral variance, and potential surface consolidation.
These deviations point towards either smaller weathering rates or younger age of the western bulge.
Rather than previously discussed rotational deformation, another possibility is an impact event (inelasticcollision) of a similar Cb-type asteroid composition. In this hypothesis, the central ridge existed andthen developed again after the western bulge-forming event due to Ryugu’s high spin rate.
Across the midlatitudes (30oN to 40oS) of Ryugu, over 48,000 boulders were identified. Major
observations include that boulders were fewer in large craters, possibly due to the low gravity of Ryugu.
There were fewer boulders (15%) in the western bulge than in other areas. Boulders showed a strong
NE-SW orientation in the northern hemisphere and NW-SE in the southern hemisphere, possibly due tothe spin direction of Ryugu (Watanabe et al., 2019). Additionally, boulders were used to determine crater
stratigraphy on Ryugu's surface. Crater centered at 16°N, 25°W; 4°S , 68°W; 18°N , 136°E is younger
than the ones centered at 1°N,30°W; 10°S , 73°W; 18°N , 149°E respectively. In the future, complete
crater stratigraphy relations will be established based on their mutual relationships.
A detailed photogeological map of Ryugu helps to identify previously unidentified features and their
spatial distribution for the first time, significantly enhancing the understanding of the asteroid's surface
and geological history. Along with this, the study also introduces a novel method for determining crater
stratigraphy on small-body asteroids. It will augment further studies, contributing valuable data for
future research.

References:
1. Ho, TM, Jaumann, R., Bibring, JP, Grott, M., Glaßmeier, KH, Moussi, A., ... & Ziach, C. (2021).
The MASCOT lander aboard Hayabusa2: The in-situ exploration of NEA (162173) Ryugu.
Planetary and Space Science , 200 , 105200.
2. Michikami, T., Honda, C., Miyamoto, H., Hirabayashi, M., Hagermann, A., Irie, T., ... & Sugita,S. (2019). Boulder size and shape distributions on asteroid Ryugu Icarus , 331 , 179-191.
3. Sugita, S., Honda, R., Morota, T., Kameda, S., Sawada, H., Tatsumi, E., ... & Tsuda, Y. (2019).
The geomorphology, color, and thermal properties of Ryugu: Implications for parent-bodyprocesses. Science , 364 (6437), eaaw0422.
4. Sugita, S., Honda, R., Morota, T., Kameda, S., Sawada, H., Tatsumi, E., ... & Tsuda, Y. (2019).
The geomorphology, color, and thermal properties of Ryugu: Implications for parent-bodyprocesses. Science , 364 (6437), eaaw0422.
5. Watanabe, S., Hirabayashi, M., Hirata, N., Hirata, N., Noguchi, R., Shimaki, Y., ... & Tsuda, Y.
(2019). Hayabusa2 arrives at the carbonaceous asteroid 162173 Ryugu —A spinning top–shaped rubble pile. Science , 364 (6437), 268-272.