The European Space Agency (ESA) and Roscosmos ExoMars mission will launch the “Rosalind Franklin” rover in 2022 for a landing on Mars in 2023.The goals of the mission are to search for signs of past and present life on Mars, investigate the water/geochemical environment as a function of depth in the shallow subsurface, and characterize the surface environment. To meet these scientific objectives while minimizing the risk for landing, a 5-year-long landing site selection process was conducted by ESA, during which eight candidate sites were down selected to one: Oxia Planum. Oxia Planum is a 200 km-wide low-relief terrain characterized by hydrous clay-bearing bedrock units located at the southwest margin of Arabia Terra. This region exhibits Noachian-aged terrains. We show in this study that the selected landing site has recorded at least two distinct aqueous environments, both of which occurred during the Noachian: (1) a first phase that led to the deposition and alteration of ∼100 m of layered clay-rich deposits and (2) a second phase of a fluviodeltaic system that postdates the widespread clay-rich layered unit. Rounded isolated buttes that overlie the clay-bearing unit may also be related to aqueous processes. Our study also details the formation of an unaltered mafic-rich dark resistant unit likely of Amazonian age that caps the other units and possibly originated from volcanism. Oxia Planum shows evidence for intense erosion from morphology (inverted features) and crater statistics. Due to these erosional processes, two types of Noachian sedimentary rocks are currently exposed. We also expect rocks at the surface to have been exposed to cosmic bombardment only recently, minimizing organic matter damage.

中文翻译：

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Oxia Planum：ExoMars“Rosalind Franklin”漫游者任务的着陆点：地质背景和预着陆解释

欧洲航天局 (ESA) 和 Roscosmos ExoMars 任务将于 2022 年发射“罗莎琳德富兰克林”漫游车，并于 2023 年登陆火星。该任务的目标是在火星上寻找过去和现在生命的迹象，调查水/地球化学环境作为浅层地下深度的函数，并表征地表环境。为了实现这些科学目标，同时最大限度地降低着陆风险，欧空局进行了为期 5 年的着陆地点选择过程，在此期间，八个候选地点被选为一个：Oxia Planum。Oxia Planum 是一个 200 公里宽的低地势地形，其特征是位于阿拉伯 Terra 西南边缘的含水粘土基岩单元。该地区展示了诺亚时代的地形。我们在这项研究中表明，选定的着陆点至少记录了两种不同的水环境，这两种环境都发生在诺亚纪时期：(1) 第一阶段导致约 100 m 层状富含粘土沉积物的沉积和蚀变(2) 在广泛分布的富含粘土的层状单元之后的河三角洲系统的第二阶段。覆盖在含粘土单元上的圆形孤立小山也可能与含水过程有关。我们的研究还详细说明了一个可能是亚马逊时代的未改变的富含镁铁质的暗抗性单元的形成，它覆盖了其他单元，可能起源于火山作用。Oxia Planum 从形态学（倒置特征）和陨石坑统计数据显示了强烈侵蚀的证据。由于这些侵蚀过程，目前有两种类型的诺亚沉积岩出露。