Preliminary geomorphological map of asteroid Ryugu

A boulder-rich asteroid, 162173 Ryugu, exhibits complicated geological and geomorphological characteristics. Using images of Optical Navigation Camera (ONC-T) onboard Hayabusa2 spacecraft, our group is working on identifying geologic features on Ryugu and understanding their general characteristics, such as non-uniform distributions of craters (as reported as [1, 2] this meeting) and boulders [3,4] and peculiar patterns of lineaments [5]. Among the most intriguing features is the equatorial ridge, which shows an almost perfect circular profile when viewed from either pole. Interestingly, the ridge is cut by some major craters with relatively distinct rims and seemingly affected by the major trough system. We developed several types of equidistant cylindrical projection maps including orthographic image, digital elevation model, and shaded relief map based on the elevation model, which are used to map these geomorphological features in two dimensions. We also use a three-dimensional shape model [6] to map these features, especially to unravel the sequences of geological events. We will report the initial results of our mapping investigation and discuss about a possible evolutionary history of this asteroid.

[1] Morota et al., this meeting, [2] Cho et al., this meeting, [3] Michikami et al., this meeting, [4] Honda et al., this meeting, [5] Kikuchi et al., this meeting, [6] Hirata et al., this meeting