In situ lunar phase curves measured by Chang’E-4 in the Von Kármán Crater, South Pole-Aitken basin

Abstract

Context. The Yutu-2 rover of the Chang’E-4 (CE-4) mission measured the lunar phase curves in the Von Kármán crater, South Pole-Aitken basin. Aims. We aim to study the photometric properties of the regolith at CE-4’s landing site and compare them with those of Chang’E-3 (CE-3) in order to understand the regolith physical properties of the two landing sites. Methods. We extracted the insitu lunar phase curves measured by CE-4 with a very wide phase angle coverage (1°–144°) and performed photometric model inversions using both the Hapke model and the Lumme-Bowell model. Results. Compared with the CE-3 measurement taken in Mare Imbrium, the CE-4 phase curves show the colorimetric opposition effect and have a steeper and narrower opposition spike. The surface regolith at the CE-4 site is much darker, more porous, more forward scattering, and has a larger slope angle (Hapke model) than that of CE-3. Conclusions. The CE-4 site may have experienced more space weathering alterations than the CE-3 site, which is consistent with their different surface model ages (~3.6 Ga for CE-4 and ~3 Ga for CE-3).