The spatial distribution of impact craters on Ryugu

TL;DR

This study provides a comprehensive global catalog of impact craters on Ryugu, revealing non-uniform crater distribution that indicates complex geological history and varying surface ages across different regions.

Contribution

The paper presents the first detailed global impact crater catalog of Ryugu using new images, and analyzes spatial variations in crater density to infer geological history.

Findings

More craters at lower latitudes than higher latitudes.

Fewer craters in the western bulge compared to the meridian.

Crater distribution suggests varying surface ages and geological activity.

Abstract

Asteroid 162173 Ryugu has numerous craters. The initial measurement of impact craters on Ryugu, by Sugita et al. (2019), is based on Hayabusa2 ONC images obtained during the first month after the arrival of Hayabusa2 in June 2018. Utilizing new images taken until February 2019, we constructed a global impact crater catalogue of Ryugu, which includes all craters larger than 20 m in diameter on the surface of Ryugu. As a result, we identified 77 craters on the surface of Ryugu. Ryugu shows variation in crater density which cannot be explained by the randomness of cratering; there are more craters at lower latitudes and fewer at higher latitudes, and fewer craters in the western bulge (160 E - 290 E) than in the region around the meridian (300 E - 30 E). This variation implies a complicated geologic history for Ryugu. It seems that the longitudinal variation in crater density simply indicates variation in the crater ages; the cratered terrain around the meridian seems to be geologically old while the western bulge is relatively young. The latitudinal variation in crater density suggests that the equatorial ridge of Ryugu is a geologically old structure; however, this could be alternatively explained by a collision with many fission fragments during a short rotational period of Ryugu in the past.