Hydrogen Quantification And Geological Mapping At Tianwen-1 Landing Site

Tianwen-1 is the first Chinese Mars exploration mission,since arriving,large orbital and in-situ data have been returned.The Utopia Planitia where the landing area is located is an important region to study the Mars dichotomy,ancient aqueous,and other scientific questions,and Tianwen-1 can support improving our understanding of those.In order to constraint the topography and geological structures,the surface soil characteristics and water-ice distribution,and the surface material composition,the orbital and in-situ data were used to study the area around the traverse path of Zhurong rover in the first 166 sols.Through the interpretation and analysis of image and elevation data,the study area is flat integrally,the height difference is～10 m,and the average slope is～3.1°.There are four kinds of geological structures,which are Transverse Aeolian Ridges(TARs),impact craters,rocky fields,and cones,suggesting that the region had experienced aeolian,impact,water/ice,or volcanism processes.TARs present an east-west spatial distribution with the windward to the north,the height is a little smaller than other places on Mars,and the surface of some TARs has a well-preserved crater.Accordingly,million years ago,the dominant wind of the landing area came from the north,and maybe the flat open terrain caused the small height of TARs,TARs have consolidated and have poor mobility.The diameter of the craters is 0.8-100 m，and the value of depth/diameter(0-0.4)is small,the images also display that the craters have been filled,and the edge of the craters is faint,therefore,these craters may be second craters or have high degradation degree.Moreover,nine rocky fields have the characteristics of high rock abundance,large roughness,and different albedo,and a cone in the southeastern part of the study area is similar to the pitted cone.Based on the laboratory data set,the LIBS hydrogen quantitative model was constructed and modified for Mars data.RMSECV of the model is～0.2,and response transformation from MarSCoDe to ChemCam was also performed.The average water content of 25 targets(including 22 soil targets)in the landing area was predicted to be～7 wt.%,which was significantly higher than the global average soil water content of Mars(～4.36 wt.%),and the hydrogen content had a good correlation with Mg.In addition,the SWIR data of seven targets with high water content have the spectral characteristics of magnesium sulfate hydrate,calcium sulfate hydrate,and pyroxene.This suggests that the composition of the landing area includes hydrated sulfate(magnesium sulfate,calcium sulfate)and pyroxene.According to the study of crater filling volume,geological structures,and previous study results,the stratigraphic division,age,and thickness estimation of the layers carried out.From top to bottom,they are loose materials layer(～430-860 Ma,～1-10 m),rocky materials layer(Amazonian period,～20 m),VBF materials layer(Late Hesperian period,～100-270 m),volcanic ridged plains materials layer(Noachian period,～800-1000 m)and basement materials layer(Early Noachian period),Especially,the region has undergone resurfacing events,and two possible formation mechanisms of volcanic ash resurfacing and mud flow resurfacing are proposed.From the topography,geological structures,and material composition of the study area,the following regional geological evolution history is obtained:In the Late Hesperian to the Amazonian period after the formation of VBF,the mud volcano erupted and covered a large area.With the evaporation of water in the mud flow,the materials in the mud flow were deposited.At the same time,it may also be accompanied by the rise and infiltration of groundwater to make the materials undergo cementation and lithification.This process may occur repeatedly and gradually form a rocky materials layer.In the late Amazonian period,water activities were limited,and eolian action became dominant and strong.The rocky materials were gradually weathered and eroded to form loose materials on the surface.Combined with the above results and analysis,a large-scale(1:500)geological map of the study area was drawn to visually display the topography,structure,age,stratum,and the Zhurong rover traverse of the study area.