T238 The Age of Small World Exploration: Major Results from Minor Planets and Other Small Solar System Bodies

Wednesday, 7 November 2018
8:00 AM - 12:00 PM
Room 236-237

THE GEOLOGIC PROPERTIES OF ASTEROID RYUGU REVEALED BY HAYABUSA2 VISIBLE MULTI-BAND IMAGING OBSERVATIONS AT MULTI-SCALES

Paper number: T238-1
Program: Technical Sessions
Time: 8:00 AM – 8:20 AM

Authors

Abstract

Hayabusa2 has conducted multi-band visible imaging observations at multiple scales from global observations at 2 m/pix in June 2018, subsequent 50-70 cm/pix observations focusing on the equatorial and polar regions in July-Aug, and 10 cm/pix observations in Aug. These observations revealed a number of important geologic properties of Ryugu, such as a classic bi-cone top shape with upright spin axis, equatorial ridge encircling the entire body, and general uniformity in visible spectra on the entire globe with very low geometric albedo (~0.043), one of the darkest surfaces in the solar system. Furthermore, this asteroid is characterized by a high abundance and variety of large boulders, particularly around the poles with decreasing number density as latitude decreases toward the equator. Close examination reveals a number of bright spots on the regolith surface and bright surfaces on large boulders, which often exhibit bluer spectra. Ryugu also has many bowl-shaped circular depressions with raised rims, which are consistent with impact craters. Furthermore, wall slumping, high circularity, and the lack of double floors at crater bottoms suggest gravity-controlled formation, though crater sizes may also be influenced by the high friction due to angular grain shapes. Preferential deficiency in small circular depressions with a similar cumulative size-frequency slope as Itokawa and Eros suggests the presence of granular medium subject to seismic shaking leading to crater erasure. The morphologic properties consistent with gravity-controlled crater formation also suggests that Ryugu may be covered with impact ejecta, which is consistent with thin regolith deposits found on many flat boulders on Ryugu. Such widely spread ejecta may be responsible for the highly uniform spectra of Ryugu’s surface. In contrast, bluer and brighter spectra are seen on vertical surfaces of the giant boulder on the south pole. Also, small bright spots in lower latitudes suggest exposure of fresh surfaces. These suggest that exposure to space may result in darkening and reddening of Ryugu material. In other words, the bluer and brighter spectra may represent of the Ryugu’s intrinsic spectra.

Acknowledgements: This study was supported by JSPS International Planetary Network. P.M. was supported by French Space Agency CNES.

Geological Society of America Abstracts with Programs. Vol. 50, No. 6

doi: 10.1130/abs/2018AM-322174

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