Mineral abundances and different levels of alteration around Mawrth Vallis,Mars

Spectral indices from OMEGA hyperspectral data show that there are two main phyllosilicates exposed in and around Mawrth Vallis:Al phyllosilicates and Fe/Mg phyllosilicates.Detailed analysis of CRISM spectra shows that Al phyllosilicates such as montmorillonite,hydrated silica,kaolinite;Fe/Mg phyllosilicates such as nontronite,saponite,serpentine are widespread on the light-toned outcrops.Though similar stratigraphical sequences,morphologies and textures are observed on both sides of Mawrth Vallis from HiRISE images,suggesting that the geological processes that formed these units must have operated at a regional scale;the multiple endmember spectral mixture analysis(MESMA) derived mineral abundance indicates that there is a higher level of alteration in the western side relative to the eastern side.We suggest that the observed phyllosilicates,stratigraphical sequences and different levels of alteration might have been caused by sedimentary deposition processes in which the composition of the external source sediment or the local solution was different,or by a pedogenic process closely related to the leaching of abundant liquid water with different chemical properties.

Progress and Applications of Visual SLAM

Visual simultaneous localization and mapping (SLAM) provides mapping and self-localization results for a robot in an unknown environment based on visual sensors, that have the advantages of small volume, low power consumption, and richness of information acquisition. Visual SLAM is essential and plays a significant role in supporting automated and intelligent applications of robots. This paper presents the key techniques of visual SLAM, summarizes the current research status, and analyses the new trends of visual SLAM research and development. Finally, specific applications of visual SLAM in restricted environments, including deep space and indoor scenarios, are discussed.

Geological context of the Chang’e-6 landing area and implications for sample analysis

Research on returned samples can provide ground truth for the study of the geological evolution history of the Moon.However,previous missions all collected samples from the near side of the Moon,which is significantly different from the far side of the Moon in terms of the thickness of the lunar crust,magma activity,and composition.Therefore,the samples from the far side of the Moon are of great significance for a comprehensive understanding of the history of the Moon.China’s Chang’e-6(CE-6)probe has successfully landed on the lunar far side and will return samples in the coming days.With the precise location of the CE-6 landing site,a detailed analysis of the geological background is conducted in this research.The landing site of CE-6 is within the Apollo crater,which is inside the largest impact basin on the Moon,i.e.,the South Pole-Aitken(SPA)basin.According to the numerical simulation of the formation process of the SPA basin,CE-6 landed at the edge of the SPA impact melting zone,which is presumably composed of impact melt of the lunar mantle.The Apollo crater subsequently excavated deep material again,which constitutes the basement of the CE-6 landing area.Later,erupted basalt covered these basement rocks,and they also constitute the main source of the CE-6 samples.Based on the dating method of crater size-frequency distribution,we find that the basalt is2.50 Ga.The CE-6 samples also possibly contain basement rocks as excavated and ejected by craters,and they can provide crucial information for our understanding of lunar geological history along with the basalt samples.

Progresses and prospects of impact crater studies

Crater is a geologic structure in solid bodies(including the terrestrial planets, moons, and asteroids) formed by hyperspeed impact, and the impact process is extremely important to the formation and evolution of these celestial bodies. This paper presents a review of the studies on remote sensing observation, formation mechanism, and scientific application of craters. On the remote sensing study of craters, the topographic characteristics of the micro-craters, simple craters, complex craters, and impact basins are described,the related parameters in the morphological studies of craters are subsequently introduced, and the distribution characteristics of the minerals and rock types during the impact excavation process are analyzed,the methods of crater identification and the crater databases on the Moon, Mars, Ceres, and Vesta are summarized. On the studies of crater formation mechanism, the general formation process of the craters is firstly described, and then the most frequently used methods are presented, and the importance of the empirical equations is also elucidated. On the scientific applications of the craters, the principle and currently utilization of the planetary surface dating method with crater size-frequency distribution are firstly presented, and the applications, including modeling the lunar regolith formation and thickness derivation of both the regolith and basalt, are reviewed. Finally, the future prospects of the formation mechanism study of the craters are discussed.

Hydrocode Simulation of the Impact Melt Layer Distribution underneath Xiuyan Crater, China

In this research, we studied the distribution of impact melt layers underneath Xiuyan crater using hydrocode simulation. The target was modeled by granite based on the rock type distribution around the crater and projector by iron, because most small and isolated terrestrial craters are formed by iron projectile. The simulated crater diameter and depth are 1 710 and 320 m, respectively, which are in good agreement with observations of 1 800 and 307 m（except for the postimpact lacustrine sedimentation）. The validated model shows that impact melt materials were first formed along the transient crater floor and wall by highshock pressure, and then refilled inward the crater along with collapse of the crater wall. The final style of impact melt materials is interbedded with shock breccia underneath the crater center, which is verified through two layers in the borehole located in the crater center.

月球南极—艾特肯盆地的形成与早期撞击历史

月球撞击构造完整地记录了内太阳系的小天体撞击历史,是研究撞击历史和撞击通量的最好样本。南极—艾特肯(SPA)盆地是月球上最大最古老的撞击盆地,其形成时间是重建月球演化历史的关键节点。SPA盆地的形成与早期撞击历史的研究,对于揭示月球外动力演化历史、建立月球演化的精确时间标尺、理解太阳系天体轨道动力学演化以及地球宜居环境演化等具有重大科学意义,是月球科学的突破口之一。本文梳理了SPA盆地等早期重大撞击事件的形成时间、SPA盆地的形成过程及全球响应、早期小天体的撞击通量等关键科学问题。提出了在月球科研站任务背景下的研究建议,并倡议采样返回与样品定年、遥感数据撞击坑统计分析、撞击成坑数值模拟相结合的研究方法。

Geospatial technologies for Chang’e-3 and Chang’e-4 lunar rover missions

This paper presents a brief overview of the geospatial technologies developed and applied in Chang’e-3 and Chang’e-4 lunar rover missions.Photogrammetric mapping techniques were used to produce topographic products of the landing site with meter level resolution using orbital images before landing,and to produce centimeter-resolution topographic products in near real-time after landing.Visual positioning techniques were used to determine the locations of the two landers using descent images and orbital basemaps immediately after landing.During surface operations,visual-positioning-based rover localization was performed routinely at each waypoint using Navcam images.The topographic analysis and rover localization results directly supported waypoint-to-waypoint path planning,science target selection and scientific investigations.A GIS-based digital cartography system was also developed to support rover teleoperation.

Topographic Mapping Capability Analysis of Moderate Resolution Imaging Camera(MoRIC)Imagery of Tianwen-1 Mars Mission

The Moderate Resolution Imaging Camera(MoRIC)onboard the orbiter of China’s Tianwen-1 Mars mission aims to map the surface of Mars globally and to explore its topography and geomorphology.This camera’s wide field of view can be used to overlap adjacent images sufficiently for topographic reconstruction.This study aimed to assess the topographic mapping potential of MoRIC images via a systematic accuracy analysis of MoRIC stereo mapping based on theoretical calculation and experimental validation.Experimental analyses were conducted using digital elevation models(DEMs)based on MoRIC images covering the Zhurong rover landing area and Mars Chart 11 region.Comparisons between these DEMs and reference DEMs revealed that the elevation accuracy of the former was approximately one ground sampling distance of the MoRIC image,which is consistent with the theoretical accuracy.Based on these results,MoRIC can be used to effectively map the Martian surface via stereo photogrammetry.These results serve as a useful guideline for topographic mapping based on MoRIC images and their application in various streams of research.