Photometric characterization of the Chang’e-3 landing site using LROC NAC images

• Published in: Icarus (New York, N.Y. 1962) Vol. 273; pp. 84 - 95
• Main Authors: Clegg-Watkins, R.N., Jolliff, B.L., Boyd, A., Robinson, M.S., Wagner, R., Stopar, J.D., Plescia, J.B., Speyerer, E.J.
• Format: Journal Article
• Language: English
• Published: Elsevier Inc 15.07.2016
• Subjects: Chinese spacecraft; Image processing; Landing; Landing sites; Moon; Moon, surface; Photometry; Reflectance; Reflectivity; Regolith; Regoliths; Spacecraft; China, People's Rep; Moon, surface; Image processing; Moon; Regoliths; Photometry
• ISSN: 0019-1035; 1090-2643
• DOI: 10.1016/j.icarus.2015.12.010

•Rocket exhaust cause increased soil reflectance at the Chang’e-3 landing site.•Reflectance changes are comparable to those of historic landing sites.•Blast zone reflectance changes are not altered over decades.•Before/after NAC images reveal a diffuse blast zone and focused blast zone.•Space weathering will eventually alter reflectance characteristics of BZs. China’s robotic Chang’e-3 spacecraft, carrying the Yutu rover, touched down in Mare Imbrium on the lunar surface on 14 December 2013. The Lunar Reconnaissance Orbiter (LRO) Narrow Angle Camera (NAC) imaged the site both before and after landing. Multi-temporal NAC images taken before and after the landing, phase-ratio images made from NAC images taken after the landing, and Hapke photometric techniques were used to evaluate surface changes caused by the disturbance of regolith at the landing site (blast zone) by the descent engines of the Chang’e-3 spacecraft. The reflectance of the landing site increased by 10±1% (from I/F=0.040 to 0.044 at 30° phase angle) as a result of the landing, a value similar to reflectance increases estimated for the Apollo, Luna, and Surveyor landing sites. The spatial extent of the disturbed area at the Chang’e-3 landing site, 2530m2, also falls close to what is predicted on the basis of correlations between lander mass, thrust, and blast zone areas for the historic landed missions. A multi-temporal ratio image of the Chang’e-3 landing site reveals a main blast zone (slightly elongate in the N–S direction; ∼75m across N–S and ∼43m across in the E–W direction) and an extended diffuse, irregular halo that is less reflective than the main blast zone (extending ∼40–50m in the N–S direction and ∼10–15m in the E–W direction beyond the main blast zone). The N–S elongation of the blast zone likely resulted from maneuvering during hazard avoidance just prior to landing. The phase-ratio image reveals that the blast zone is less backscattering than surrounding undisturbed areas. The similarities in magnitude of increased reflectance between the Chang’e-3 landing site and the Surveyor, Apollo, and Luna landing sites suggest that lunar soil reflectance changes caused by interaction with rocket exhaust are not significantly altered over a period of 40–50years. The reflectance changes are independent of regolith composition, indicating that they are caused by a change in the physical properties of the regolith, likely microscopic to macroscopic smoothing of the surface, and possibly a change in surface maturity by removal of highly mature very fine-grained regolith components.