Laboratory Spectroscopic Studies Of Lunar Minerals And Water Ice Simulants And Their Remote Sensing Applications

Chemical composition and mineralogy of the lunar interior are the key to understand the evolution of lunar magma ocean and specifically the early history of building processes of lunar crust and mantle.The first lunar farside roving mission,Chang’e-4,provides unprecedented opportunity to acquire the chemical and mineralogical information of lunar lower crust or even mantle exposed in Von Karman crater in South Pole-Aitken basin.According to the spectral deconvolution of VNIS(Visible and near-infrared imaging spectrometer)data,different mineral proportions have been derived and different sources(olivine and low-Ca pyroxene(LCP)-rich mantle material or plagioclase and LCP-rich crustal impact melt)have been put forward to interpret their origins.Therefore,the relative proportions of olivine,plagioclase,and pyroxene are controversial.In this thesis,we prepared a series of lunar soil analogs in the laboratory by mixing four major silicate minerals occurred on the Moon,i.e.,LCP,high-Ca pyroxene(HCP),olivine,and plagioclase based on the mineral assemblages from remote sensing studies of the Chang’e-4 landing site by SELENE Kaguya MI data.Visible and near-infrared(VNIR)spectra of analog samples were measured by ASD spectrometer and backup VNIS(a prototype similar to that one onboard CE-4 Yutu-2 rover)with intent to evaluate the performance of the in-flight VNIS and constrain the mineralogy at CE-4 landing site.We find that the olivine content in the mineral mixtures can be evaluated by spectral parameters like band area ratios(BAR).With deconvolution of the two datasets from ASD and prototype VNIS by Modified Gaussian Model(MGM),we find that the modeled band centers(BCs)and HCP/LCP absorption peak strength ratio at～1 and～2 μm of VNIR spectra of lunar soil analog samples present obvious linear relationships with the real mixing ratio of HCP/LCP.In addition,a lower limit of 15%for olivine content(HCP+LCP+OL=100%)is obtained by MGM deconvolution of our laboratory studies.This work also provides a series of experimental datasets and reference parameters of MGM spectral deconvolution for mineralogical interpretations of CE-4 VNIS data.The correlations of HCP/LCP ratios and single scatter albedos(SSA)obtained by Hapke radio transfer model also exhibit good linear relationship.Based on above laboratory studies with MGM deconvolution,we find that the lunar soils and rocks have HCP/LCP ratios of 0.60～0.66 and olivine content is 35%～40%.With Hapke model applied to the lunar rock spectra acquired by Yutu-2 VNIS,we obtained similar mafic mineral results as MGM(i.e.,the HCP/LCP is 0.66)at CE-4 landing site.The form of water ice occurrence in permanently shadowed regions(PSR)of lunar polar regions is an unsolved problem in the exploration of lunar water ice.The reflectance data of PSR collected by Chandrayaan-1 M3(Moon Mineralogy Mapper)have low signal to noise ratios(SNR)and active laser(i.e.,LOLA,lunar orbiter laser altimeter)reflectance data are limited in single band and can’t reflect complete spectral information of water ice.In order to better constrain the occurrence form of water ice in PSR of lunar polar regions,laboratory spectroscopic studies on lunar soils analogs and artificial water ice with five different grain sizes are conducted.By comparison of artificial water ice spectra with M3 observations of lunar PSR,we suggest that water ice signals from lunar polar regions are from ice-soil mixture dominated by water ice with grain sizes ranging from 100～300 μm,which is an important reference for exploration of lunar water ice in the future.