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我国首个火星探测任务天问一号探测器由环绕器、着陆器和巡视器(祝融号火星车)组成。祝融号火星车于2021年5月15日成功登陆火星北半球乌托邦平原南部的预选着陆区。乌托邦平原过去可能存在具备孕育生命的环境,祝融号火星车在该地区开展巡视探测,具有丰富的科学价值。为了给祝融号火星车和天问一号环绕器今后获取的就位和遥感探测数据的分析和解释提供有关着陆区的地质背景,本文利用已有的遥感影像和产品,详细分析了祝融号火星车着陆点周边50 km区域的地质特征,并制作了着陆区地质图。着陆区主要存在撞击坑、横向风成脊、槽沟和锥形丘等地貌。在200 m尺度上,整个着陆区地势南高北低,地形较为平缓,十分有利于后续巡视探测。着陆区热惯量相对较低,地表风化层仅存在少量呈半掩埋状的岩石,表明该区域的风化层易于受到热扰动的影响。受高光谱遥感影像分辨率和(或)矿物吸收特征的限制,着陆区的矿物类型和丰度暂时未知,急需火星车开展就位探测以填补目前的空缺。综合乌托邦平原的撞击成因和火星北半球可能存在的巨大古海洋及其后续演化,本文提出乌托邦平原在火星的各个地质时期主要经历了撞击盆地形成(前诺亚纪)、流水沉积物填充(诺亚纪)、撞击坑等典型地貌发育(西方纪)、火山物质部分覆盖(亚马逊纪)等较为复杂的地质改造和演化过程。结合着陆区的地质特征和祝融号火星车搭载的科学载荷,本文建议火星车将着陆区南部的横向风成脊、槽沟和锥形丘分别作为火星车的短期、中期和远期优先探测对象,从形貌学、矿物学、地层学和气候学等多方面对它们开展综合探测分析,确定它们的真正成因或归类。祝融号火星车的就位探测成果将极大的丰富行星科学领域对乌托邦平原地质演化过程的认识,甚至可以为过去可能存在的古海洋和生命宜居环境的综合评价提供支撑。
China"s first Mars exploration mission Tianwen-1 probe is composed of an orbiter, a lander and a rover (Zhurong). The Zhurong rover successfully landed on the pre-selected landing area in the southern Utopia Planitia in the Martian northern hemisphere on May 15, 2021. The Utopia Planitia might have an environment capable of nurturing life in the past, thus the traversing and in situ exploration by the Zhurong rover in this region will produce wealthy scientific outputs. To provide context for the analysis and interpretation of the in situ measured and the remotely sensed data acquired by the rover and the orbiter, this article uses available remote sensing images and products to analyze the geological characteristics within the surrounding 50 km of the landing site of the Zhurong rover, and a geological map was produced. The main landforms in the landing area are impact craters, troughs, cones, and traverse aeolian ridges. At a baseline of 200 m, the general elevation is high in the south and low in the north, and the terrain is relatively flat, which is very suitable for the follow-up traversing and in situ measuring. The thermal inertia of the landing area is relatively low, and there are only a few semi-buried rocks on the surface of the regolith, indicating the surface regolith is vulnerable to thermal disturbance. Limited by the low resolution of hyperspectral images and/or the lack of absorption features of the surface materials, the compositions and abundances of the minerals in the landing area are temporarily unknown, thus the in-situ measurements by the rover is urgently needed to fill the current vacancy. Considering the impact-origin of the Utopian basin,the possible existence of a giant paleo-ocean and its subsequent evolution in the northern hemisphere of Mars, this paper proposes that the Utopian Planitia had mainly experienced a relative complicated geological transformation and evolution, including formation of impact basin (Pre-Noachian), infilling of flowing water sediments (Noachian), development of typical landforms, e.g., impact craters (Hesperian) and partial coverage of volcanic materials (Amazonian). Combining the geological characteristics of the landing area and the scientific payloads carried by the Zhurong rover, this paper suggests that the rover should choose the traverse aeolian ridge, the trough and the pitted cone in the southern of the landing area as the rover"s short-term, mid-term, and long-term priority detection targets, respectively. Their formation mechanisms or classifications may thus be determined through a comprehensive analysis from the viewpoint of morphology, mineralogy, stratigraphy, and climatology. The results of the in-situ measurements will greatly promote the understanding of the geological evolution of the Utopia Planitia in the planetary science community, and can even provide support for a comprehensive evaluation of the possible paleo-ocean and habitable environment in the past.