Return to the Moon:New perspectives on lunar exploration

Lunar exploration is deemed crucial for uncovering the origins of the Earth-Moon system and is the first step for advancing humanity’s exploration of deep space.Over the past decade,the Chinese Lunar Exploration Program(CLEP),also known as the Chang’e(CE)Project,has achieved remarkable milestones.It has successfully developed and demonstrated the engineering capability required to reach and return from the lunar surface.Notably,the CE Project has made historic firsts with the landing and on-site exploration of the far side of the Moon,along with the collection of the youngest volcanic samples from the Procellarum KREEP Terrane.These achievements have significantly enhanced our understanding of lunar evolution.Building on this success,China has proposed an ambitious crewed lunar exploration strategy,aiming to return to the Moon for scientific exploration and utilization.This plan encompasses two primary phases:the first crewed lunar landing and exploration,followed by a thousand-kilometer scale scientific expedition to construct a geological cross-section across the lunar surface.Recognizing the limitations of current lunar exploration efforts and China’s engineering and technical capabilities,this paper explores the benefits of crewed lunar exploration while leveraging synergies with robotic exploration.The study refines fundamental lunar scientific questions that could lead to significant breakthroughs,considering the respective engineering and technological requirements.This research lays a crucial foundation for defining the objectives of future lunar exploration,emphasizing the importance of crewed missions and offering insights into potential advancements in lunar science.

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.

Mineralogical evidence of water activity in the northern lowlands of Mars based on inflight-calibrated spectra from the Zhurong rover

Hydrated minerals provide direct indications of the early Martian water environment. The various clay minerals and evaporite salts found to date are mainly exposed in the ancient southern highlands of Mars. While it is believed that the area of the northern lowlands could have hosted a global ocean in the past, its surface is covered with a layer of spectrally nonabsorbing materials, and orbital hyperspectral remote sensing has found only sparse evidence for the presence of water. China's first Mars exploration mission, Tianwen-1, landed in the putative ancient shoreline zone of the northern lowlands of Mars. Its rover,Zhurong, conducted high-spatial-resolution reconnaissance to reveal the geological and environmental evolution of this region.Owing to frequent dust storms, not only is the Martian surface covered with dust, but also the spectral calibration panels on the rover are affected by dust coverage. Data from the shortwave infrared(SWIR) spectrometer onboard the rover are also affected by other environmental factors such as instrumental temperature changes and atmospheric carbon dioxide absorption. This study recalibrated the in situ SWIR data to minimize the impact of the above factors. The recalibrated spectral data show that the reflectance of the landing area falls within the normal range of Martian soil, and confirm the presence of several important absorption peaks. The absorption characteristics indicate the presence of polyhydrated sulfates, gypsum, and hydrated silicates in the surface materials along the rover track, with sulfate content of <27–39 wt.%. Our results further confirm past activity of liquid water in the Zhurong rover landing area, providing mineralogical evidence supporting hypotheses related to underground water or an ancient shoreline.

Lunar Evolution Analysis Based on Numerical Simulations of Typical Lunar Impact Craters

Impact craters are one of the most important landforms on the lunar surface,playing a crucial role in the formation and later evolution of the Moon.For example,as a primary source of remote sensing observations and lunar samples,lunar regolith is predominantly composed of impact ejecta.Based on their morphologies,lunar impact craters with increasing sizes can be classified into simple craters,complex craters,and multiring basins,and they play different roles in lunar evolution.In our study,we conducted numerical simulations of the South Pole-Aitken basin and the Orientale basin on the lunar surface,as well as the Aristarchus complex crater and the Zhinyu simple crater.The resultant effects of them are further analyzed.Because Zhinyu crater is relatively close to the Chang’e-4 landing site,while Aristarchus crater is relatively close to the Chang’e-5 landing site,their simulation results have direct significance for interpreting the corresponding exploration data from both missions.The numerical simulation results demonstrate that the formation of large basins not only affects the subsurface structure within the basin but also significantly disturbs the surrounding geological layers.Complex and simple craters mainly disturb the subsurface layers within the crater,but complex craters can cause uplift of the underlying strata.These impact processes dominate the primary geological framework of the lunar surface,depositing ejecta materials of varying thicknesses from different depths,which has important implications for future sample collection missions.In conclusion,impact processes are one of the primary driving forces in the lunar evolution.

SHARAD study on the structures and permittivity of a buried impact crater in Martian Central Elysium Planitia

The Elysium Planitia,located in the transition zone between the northern and southern hemispheres,is one of the key areas for studying the stratigraphic structure and geological history of Mars.Previous studies have shown that this plain has undergone complex surface modification processes including fluvial and volcanic processes,and systematic progress has been made in the study of macro-geological processes.However,there are relatively few studies on the regional structure of the plain,which restricts our understanding of the regional geological processes.A buried impact crater in the central part of the Elysium Planitia could have recorded the surface modification process since the formation of the impact crater,however,it is difficult to distinguish the subsurface stratigraphy due to the weak orbital radar reflection signal.In this study,we denoised Shallow Radar data and obtained a radargram with clear subsurface reflectors.We estimated the permittivity of subsurface materials via a multilayer reflection model.The results show that two subsurface reflectors divide the structure of the buried impact crater into three layers(overlying layer,underlying layer,and bottom layer).The shallow subsurface reflector covers almost the whole impact crater,while the deep subsurface reflector covers only the southwest part of the impact crater.Combining the permittivity inversion results with the geological background of lava activity in the Elysium Planitia area,we argue that the overlying layer may be a mixture of regolith and lava flow with low density,while the underlying layer and bottom layer are dense lava flows.The reflector between the underlying layer and bottom layer is probably a thin deposit derived from weathering between two lava activities,and its possible formation mechanism is as follows:the crater rim and peripheral ejecta has undergone relatively strong wind erosion and the eroded material was transport to the southwestern part of the impact crater,forming continuous thin deposits,between the emplacements of two lava flows.This is consistent with the wind erosion environment prevailing at low latitudes in the Late Amazonian of Mars.This study uses processed orbital radar data,dielectric property inversion,and geological structure interpretation of regional buried impact craters as a local example to demonstrate how radar data can be used to understand regional depositional processes,and it serves as a reference for studying the geological history of similar regional structures on Mars.

Key Questions of Solar Wind-Moon Interaction

Key questions on solar wind-Moon interaction are reviewed.As the nearest celestial body to Earth,Moon’s space environment is distinctive to Earth’s mainly because of lack of a significant atmosphere/ionosphere and a global magnetic field.From a global respective,solar wind can bombard its surface,and the solar wind materials cumulated in the soil record the evolution of the Solar System.Many small-scale remanent magnetic fields are scattered over the lunar surface and,just as planetary magnetic fields protect planets,they are believed to divert the incident solar wind and shield the local lunar surface beneath,thus producing unique local surface environment that is critical to activities of human beings/facilities,thus providing unique landing sites to explore the origins of lunar swirls and remanent magnetic fields.Evidences have hinted that this local interaction,however,may be also distinct with the interacting scenario on planets,and the specific process has not been revealed because of lack of in situ observations in the near-Moon space or on the ground.The global and local solar wind interactions of the Moon represent 2 types of characteristic interaction of celestial bodies with stellar wind in deep space,i.e.,the interactions of nonmagnetized bodies and of small-scale magnetized bodies,both of which may occur on asteroids and Mars.The deep-space celestial bodies,either difficult or impossible to reach for human beings or artificial satellites,are hard to measure,and the exploration of the Moon can reveal the mystery of stellar wind interaction on these bodies.

地质学科未来5~10年发展战略:趋势与对策

当代地球科学的内涵和外延已经拓展到涵盖整个固体地球内部及外部层圈形成演化及与资源能源富集、生态环境变迁、地球宜居性和社会可持续发展相关的地球系统科学问题.随着人类社会经济高速发展,与地球相关的资源能源、气候环境、地质灾害等问题日益突出.为了适应新时代地球科学发展形势,在地球系统科学理论框架下,准确分析我国地球科学未来5~10年的发展趋势、明确战略目标和优先发展领域,不仅能够大力促进和强化我国地球科学的发展、赶超世界领先水平、早日实现从地质大国到地质强国的转变,而且对于保障国家矿产能源安全、助推国家经济建设和人类社会可持续发展具有重大意义.

月球内部圈层结构探测及关键技术挑战

地外天体的内部结构是了解其自身演化奥秘的钥匙,能够为人们深入认识地球自身的演化规律提供重要参考。地外天体内部结构探测是光学、遥感、采样返回等深空探测任务的重要补充和拓展。阿波罗时代的月震仪为揭示月球内部的奥秘做出了卓越贡献,然而,受到当时硬件水平的限制,有关月球内部圈层结构的探测结果至今仍然存在很大争议,严重制约了月球科学的发展。我国嫦娥七号任务拟对月球南极进行探测,随后逐步建立月球科研站,期间将布设我国第一台月震仪,以探测月球内部圈层结构及状态。本文阐述了月球内部结构探测的重要意义,列举了月震仪研制和布设可能面临的困难,分析了潜在问题的应对措施,提出了后续科学研究需要关注的问题,并给出了系列建议。本文旨在激发更多学者关注和从事月球及行星内部结构探测事业,以促进我国在相关研究领域的稳步前进,争列国际学术前沿。

月球科研站的关键科学问题

基于第302期“双清论坛”,本文总结了基于月球科研站的科学研究进展,围绕月球地质、近月空间环境、月基观测、月基生命实验和资源利用等领域,梳理了月球科研站的研究方向及总体科学目标,凝练了该领域未来5~10年的关键科学问题,探讨了前沿研究方向和发展战略。

曼桂陨石的岩石矿物学和冲击变质特征

曼桂陨石是2018年6月降落在云南省西双版纳傣族自治州的目击降落型陨石.陨石样品具有新鲜的熔壳,内部呈浅灰色,可见黑色冲击熔融细脉.该陨石主要由橄榄石、辉石、长石以及较少的铁镍金属、陨硫铁、磷灰石等组成.手标本虽可见球粒特征,但背散射电子图像显示球粒界线模糊,残余球粒为斑状橄榄石球粒,基质呈现强烈重结晶特征,次生长石粒度较大,橄榄石和辉石的化学成分均一,可判定其岩石类型为6型.橄榄石的平均Fa值为25.1±0.3(n=71),辉石的平均Fs值为21.1±0.3(n=58),金属含量低,属于L化学群.因此,曼桂陨石是L6型普通球粒陨石.曼桂陨石遭受过强烈的冲击,冲击熔脉和熔融囊广泛发育,熔脉宽度可达600μm.熔脉内及边部的长石已经转变成熔长石,且部分长石转变成硬玉;发现辉石的镁铁榴石高压相,与硬玉伴生.根据这些强烈冲击变质特征,将曼桂陨石的冲击变质强度划分为S5级.尚未在熔脉及边部发现橄榄石、磷酸盐的高压相矿物.这些高压矿物相的缺失,可能是由于该陨石在冲击熔融后的冷却速率较慢,形成的高压相矿物发生了退变质.这些特征表明,曼桂陨石经历过强烈的撞击熔融事件,为研究其母体的撞击历史和高压相的形成机制提供了重要标本.

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。

New Lunar Samples Returned by Chang’e-5:Opportunities for New Discoveries and International Collaboration

On December 16^(th),2020 at 17:59 UTC,the sample capsule of Chang’e-5 successfully landed at Dorbod Banner,Inner Mongolia,China.It is a milestone for the Chinese Lunar Exploration Program(CLEP),which has achieved the goals of its first three phases:orbiting,landing,and sample return.China becomes the third country to return samples from the Moon after the United States and the Soviet Union.Forty-four years since the Luna 24 mission in 1976,new lunar samples have been returned to Earth.