Venus is Earth’s closest planetary neighbour and both bodies are of similar size and mass. As a consequence, Venus is often described as Earth’s sister planet. But the two worlds have followed very different evolutionary paths, with Earth having benign surface conditions, whereas Venus has a surface temperature of 464 °C and a surface pressure of 92 bar. These inhospitable surface conditions may partially explain why there has been such a dearth of space missions to Venus in recent years. The oxygen isotope composition of Venus is currently unknown. However, this single measurement ( Δ 17 O $\Delta ^{17}\text{O}$ ) would have first order implications for our understanding of how large terrestrial planets are built. Recent isotopic studies indicate that the Solar System is bimodal in composition, divided into a carbonaceous chondrite (CC) group and a non-carbonaceous (NC) group. The CC group probably originated in the outer Solar System and the NC group in the inner Solar System. Venus comprises 41% by mass of the inner Solar System compared to 50% for Earth and only 5% for Mars. Models for building large terrestrial planets, such as Earth and Venus, would be significantly improved by a determination of the Δ 17 O $\Delta ^{17}\text{O}$ composition of a returned sample from Venus. This measurement would help constrain the extent of early inner Solar System isotopic homogenisation and help to identify whether the feeding zones of the terrestrial planets were narrow or wide. Determining the Δ 17 O $\Delta ^{17}\text{O}$ composition of Venus would also have significant implications for our understanding of how the Moon formed. Recent lunar formation models invoke a high energy impact between the proto-Earth and an inner Solar System-derived impactor body, Theia. The close isotopic similarity between the Earth and Moon is explained by these models as being a consequence of high-temperature, post-impact mixing. However, if Earth and Venus proved to be isotopic clones with respect to Δ 17 O $\Delta ^{17}\text{O}$ , this would favour the classic, lower energy, giant impact scenario. We review the surface geology of Venus with the aim of identifying potential terrains that could be targeted by a robotic sample return mission. While the potentially ancient tessera terrains would be of great scientific interest, the need to minimise the influence of venusian weathering favours the sampling of young basaltic plains. In terms of a nominal sample mass, 10 g would be sufficient to undertake a full range of geochemical, isotopic and dating studies. However, it is important that additional material is collected as a legacy sample. As a consequence, a returned sample mass of at least 100 g should be recovered. Two scenarios for robotic sample return missions from Venus are presented, based on previous mission proposals. The most cost effective approach involves a “Grab and Go” strategy, either using a lander and separate orbiter, or possibly just a stand-alone lander. Sample return could also be achieved as part of a more ambitious, extended mission to study the venusian atmosphere. In both scenarios it is critical to obtain a surface atmospheric sample to define the extent of atmosphere-lithosphere oxygen isotopic disequilibrium. Surface sampling would be carried out by multiple techniques (drill, scoop, “vacuum-cleaner” device) to ensure success. Surface operations would take no longer than one hour. Analysis of returned samples would provide a firm basis for assessing similarities and differences between the evolution of Venus, Earth, Mars and smaller bodies such as Vesta. The Solar System provides an important case study in how two almost identical bodies, Earth and Venus, could have had such a divergent evolution. Finally, Venus, with its runaway greenhouse atmosphere, may provide data relevant to the understanding of similar less extreme processes on Earth. Venus is Earth’s planetary twin and deserves to be better studied and understood. In a wider context, analysis of returned samples from Venus would provide data relevant to the study of exoplanetary systems.

中文翻译：

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金星的氧同位素组成是什么？从地球“姐妹”星球返回样本的科学案例

金星是地球最近的行星邻居，两个天体的大小和质量相似。因此，金星经常被描述为地球的姊妹行星。但是这两个世界遵循了截然不同的进化路径，地球的表面条件良好，而金星的表面温度为 464°C，表面压力为 92 巴。这些不适宜居住的地表条件可以部分解释为什么近年来金星太空任务如此缺乏。金星的氧同位素组成目前未知。然而，这个单一的测量（ Δ 17 O $\Delta ^{17}\text{O}$ ）对于我们理解大型类地行星是如何建造的具有一阶意义。最近的同位素研究表明太阳系的成分是双峰的，分为碳质球粒陨石（CC）组和非碳质（NC）组。CC群可能起源于外太阳系，NC群起源于内太阳系。金星占太阳系内部质量的 41%，而地球为 50%，火星仅为 5%。通过确定从金星返回的样本的 Δ 17 O $\Delta ^{17}\text{O}$ 组成，可以显着改善用于建造大型类地行星（例如地球和金星）的模型。这种测量将有助于限制早期内太阳系同位素同质化的程度，并有助于确定类地行星的供给带是窄还是宽。确定金星的 Δ 17 O $\Delta ^{17}\text{O}$ 组成也对我们理解月球如何形成具有重要意义。最近的月球形成模型引发了原地球与源自太阳系内部的撞击体 Theia 之间的高能量撞击。这些模型将地球和月球之间的同位素相似性解释为高温、撞击后混合的结果。然而，如果地球和金星被证明是关于 Δ 17 O $\Delta ^{17}\text{O}$ 的同位素克隆，这将有利于经典的、低能量的、巨大的撞击场景。我们回顾了金星的表面地质，目的是确定机器人样本返回任务可能瞄准的潜在地形。虽然潜在的古老 tessera 地形将具有重大的科学意义，但需要尽量减少金星风化的影响，有利于对年轻的玄武质平原进行采样。就标称样品质量而言，10 克足以进行全方位的地球化学、同位素和年代测定研究。但是，重要的是要收集其他材料作为遗留样本。因此，应回收至少 100 g 的返回样品质量。根据之前的任务建议，提出了两种来自金星的机器人样本返回任务的场景。最具成本效益的方法涉及“抓起即走”策略，要么使用着陆器和单独的轨道器，要么可能只是一个独立的着陆器。样本返回也可以作为研究金星大气的更雄心勃勃的扩展任务的一部分来实现。在这两种情况下，获取地表大气样本以确定大气-岩石圈氧同位素不平衡的程度至关重要。表面取样将通过多种技术（钻孔、勺，“真空吸尘器”设备）以确保成功。地面操作不会超过一小时。对返回样本的分析将为评估金星、地球、火星和灶神星等较小天体演化之间的异同提供坚实的基础。太阳系提供了一个重要的案例研究，说明两个几乎相同的天体，地球和金星，如何有如此不同的演化。最后，拥有失控的温室大气的金星可能会提供与理解地球上类似的不太极端的过程相关的数据。金星是地球的双胞胎，值得更好地研究和理解。在更广泛的背景下，对来自金星的返回样本的分析将提供与系外行星系统研究相关的数据。地面操作不会超过一小时。对返回样本的分析将为评估金星、地球、火星和灶神星等较小天体演化之间的异同提供坚实的基础。太阳系提供了一个重要的案例研究，说明两个几乎相同的天体，地球和金星，如何有如此不同的演化。最后，拥有失控的温室大气的金星可能会提供与理解地球上类似的不太极端的过程相关的数据。金星是地球的双胞胎，值得更好地研究和理解。在更广泛的背景下，对来自金星的返回样本的分析将提供与系外行星系统研究相关的数据。地面操作不会超过一小时。对返回样本的分析将为评估金星、地球、火星和灶神星等较小天体演化之间的异同提供坚实的基础。太阳系提供了一个重要的案例研究，说明两个几乎相同的天体，地球和金星，如何有如此不同的演化。最后，拥有失控的温室大气的金星可能会提供与理解地球上类似的不太极端的过程相关的数据。金星是地球的双胞胎，值得更好地研究和理解。在更广泛的背景下，对来自金星的返回样本的分析将提供与系外行星系统研究相关的数据。对返回样本的分析将为评估金星、地球、火星和灶神星等较小天体演化之间的异同提供坚实的基础。太阳系提供了一个重要的案例研究，说明两个几乎相同的天体，地球和金星，如何有如此不同的演化。最后，拥有失控的温室大气的金星可能会提供与理解地球上类似的不太极端的过程相关的数据。金星是地球的双胞胎，值得更好地研究和理解。在更广泛的背景下，对来自金星的返回样本的分析将提供与系外行星系统研究相关的数据。对返回样本的分析将为评估金星、地球、火星和灶神星等较小天体演化之间的异同提供坚实的基础。太阳系提供了一个重要的案例研究，说明两个几乎相同的天体，地球和金星，如何有如此不同的演化。最后，拥有失控的温室大气的金星可能会提供与理解地球上类似的不太极端的过程相关的数据。金星是地球的双胞胎，值得更好地研究和理解。在更广泛的背景下，对来自金星的返回样本的分析将提供与系外行星系统研究相关的数据。可能会有如此不同的演变。最后，拥有失控的温室大气的金星可能会提供与理解地球上类似的不太极端的过程相关的数据。金星是地球的双胞胎，值得更好地研究和理解。在更广泛的背景下，对来自金星的返回样本的分析将提供与系外行星系统研究相关的数据。可能会有如此不同的演变。最后，拥有失控的温室大气的金星可能会提供与理解地球上类似的不太极端的过程相关的数据。金星是地球的双胞胎，值得更好地研究和理解。在更广泛的背景下，对来自金星的返回样本的分析将提供与系外行星系统研究相关的数据。