火星表面含水矿物探测进展

火星表面含水矿物类型识别和空间分布特征研究对圈定火星表面生命活动有利区域和探索可能存在的火星生命形式具有重要科学意义。本文总结了20世纪90年代以来火星表面含水矿物的探测进展,从火星轨道器光谱仪遥感探测、着陆器和巡视器就位探测两方面介绍了矿物探测使用的数据源,重点阐述了目前火星表面已经探测到的各类含水硅酸盐矿物、硫酸盐矿物、碳酸盐矿物、氯盐及高氯酸盐矿物等含水矿物的光谱特征、矿物具体类别及分布特征,分析了火星表面含水矿物定量反演的主要方法与地质意义。最后从比较行星学角度倡议开展地球和火星含水矿物形成环境和形成过程的类比研究。

Advances in aqueous minerals detection on Martian surface

Aqueous minerals are either minerals that form in water or formations that are related to water.The type of aqueous mineral depends on temperature,salinity,PH,and composition of the parent rock at their forming time,which provides important clues to understanding the past aqueous environments of Mars,delineating advantageous regions for life activities,and even searching for possible existing Martian life.Therefore,studies on aqueous mineral identification and spatial distribution pattern are of considerable scientific significances. This paper provides a comprehensive overview of the advances of aqueous minerals detection on Martian surface since the 1990s.First,the major specifications of two data sources for mineral detection are introduced,including orbital spectrometers (TES,THEMIS, OMEGA,and CRISM) and in-situ landers/rovers (MPF/Sojourner,Spirit,Opportunity,Phoenix,and Curiosity).The spectrometers utilize either emission features in thermal infrared (TIR) or reflectance absorption characteristics in visible/near-infrared (VNIR) to identify and discriminate mineral types.Landers and rovers equipped with scientific instruments carry out the in-situ measurement to provide detailed component identification,abundance detection,and other analyses on the Martian surface soil,minerals,and rocks.Second,the spectral features,specific types,and distribution patterns of aqueous minerals detected on Martian surface are illustrated in detail as bound water,adsorbed water,and structural OH in aqueous minerals can be remotely detected via their unique spectral characteristics.Although aqueous minerals are widespread on Mars,they are concentrated in the Noachian southern highlands.At present,the aqueous minerals detected and verified on Martian surface from orbital spectrometers and landers/rovers can be classified as hydrous silicate minerals,sulfates,carbonates,chlorides,and perchlorates.Third,the major aqueous mineral quantitative retrieval methods,including absorption band depth conversion and spectral unmixing algorithms,are introduced.Compared with the linear unmixing model,the nonlinear spectral unmixing model can characterize mineral composition and retrieval mineral abundance with higher precision;therefore,it has been extensively used for the quantitative retrieval of aqueous mineral on Martian surface.The most commonly used nonlinear spectral unmixing models are the Hapke and Shkuratov models. The retrieval works provide fine quantitative data for inferring the formation and evolution history of aqueous mineral on Martian surface. However,numerous limitations exist,which are still important and difficult issues in aqueous mineral detection and retrieval via remote sensing.Furthermore,the retrieval advances at global and local scales,as well as their geological implications for Mars,are summarized.The detection of aqueous minerals confirms the existence of past water solution environment on Martian surface,and the phenomenon of diverse aqueous mineral categories that formed in various geomorphologies and geological contexts gradually changes over time reveals the evolution diversity of the chemical properties of water solution.Considering these two conditions,the paper finally proposes an analog study between Earth and Mars that should be carried out from the viewpoint of comparative planetology on the formation environment and process of aqueous minerals,which has important reference significance for the Mars exploration mission of China that is planned to be launched in 2020.