On February 25th, a team of scientists from Guangzhou University, the Chinese Academy of Sciences, Tongji University, Pennsylvania State University, and the University of California, Berkeley, published a study titled "Ancient ocean coastal deposits imaged on Mars" in the prestigious international journal "Proceedings of the National Academy of Sciences (PNAS)." The research indicates that subsurface deposits resembling coastal sediments have been detected beneath the landing site of China's Zhurong rover in the southern Utopia Planitia region on Mars. These deposits, located 10 to 35 meters below the surface, provide the most direct evidence to date for the existence of an ancient ocean in Mars' mid-to-low latitude regions.
China's first Mars rover, Zhurong, landed on southern Utopia Planitia on May 15th, 2021, at 109.925°E, 25.066°N. Equipped with a dual-frequency ground penetrating radar (GPR), Zhurong was designed to explore subsurface structures and potential water-ice deposits. The low-frequency channel (15-95 MHz) of the radar can penetrate up to 80 meters below the surface.
By analyzing the low-frequency radar data from Zhurong, the researchers identified 76 subsurface dipping reflectors within a depth range of 10 to 35 meters below the surface along the rover's path. These reflectors exhibit the following characteristics: (1) They are widely and evenly distributed, covering an area exceeding 1.3 kilometers; (2) Multiple parallel reflectors can be observed at different depths at the same location; (3) All reflectors are inclined toward the lower northern direction, with angles ranging from 6° to 20°, averaging 14.5°.
The presence of these extensive deposits suggests that wave-driven coastal transport provides a stable net influx of sediment to the shoreline, forming prograding layers. Such structures can only form in a large, stable body of water, rather than through localized and transient melting events. This study not only provides key subsurface evidence for an ancient ocean on Mars' northern plains but also reveals that Mars once experienced a long-lasting warm and humid climate. This implies that Mars maintained conditions suitable for liquid water, including appropriate temperature and atmospheric pressure, for extended periods—far beyond the previously estimated short-lived melting events. Additionally, the dielectric properties of the coastal deposits are consistent with those of fine and medium sand particles on Earth, further confirming their marine sedimentary nature.
The most significant implication of this discovery is the expansion of evidence for liquid water on Mars from the remote polar regions to the more habitable mid-to-low latitude areas. If an ocean once existed here, large amounts of water may have been trapped as subsurface ice following climatic changes. This could provide a potential source of water for future Martian bases. Compared to the polar regions, mid-to-low latitude areas have more favorable lighting and temperature conditions for human activities. Access to these ancient ocean deposits could significantly reduce the costs of constructing and maintaining Martian bases. Moreover, these ancient deposits preserve a historical record of Mars' climate changes, helping us understand how Mars transitioned from a warm and humid environment to its current cold and dry state. This knowledge could guide future efforts to terraform Mars and achieve long-term sustainable human habitation.
Source: Lingnan On the Cloud
2月25日，来自广州大学、中国科学院、同济大学、宾夕法尼亚州立大学以及加利福尼亚大学伯克利分校等机构的科学家团队在国际综合类顶刊《美国国家科学院院刊》发表题目为“Ancient ocean coastal deposits imaged on Mars”的研究论文表明，位于火星北半球乌托邦平原南部的“祝融号”着陆区，地下10-35米深处存在多层倾斜沉积结构。这些地质特征与地球海岸沉积物高度相似，为火星中低纬度地区曾存在古代海洋提供了迄今最直接的地下证据。
中国首辆火星车——祝融号于2021年5月15日着陆于乌托邦平原南部（东经109.925°，北纬25.066°）。祝融号搭载的火星次表层穿透雷达是一种双频探地雷达系统，旨在探测地下结构和可能存在的水冰。其中低频通道（15-95 MHz）能够探测地表以下80m的深度。
本研究通过分析火星车穿透雷达低频通道的实测数据，在祝融号沿途地表以下10-35米深度范围内识别出76个地下倾斜反射体。这些反射体具有以下特征：（1）空间分布广泛且均匀，覆盖范围超过1.3公里；（2）在相同位置的不同深度可观测到多个平行分布的反射体；（3）所有反射体均呈现向北低地方向倾斜的特征，倾角分布在6°至20°之间，平均倾角为14.5°。
这些沉积物的大规模存在表明，风浪驱动的沿岸输送为海岸线提供了稳定的泥沙净流入，并形成了海岸线前积层，这种结构只有在持久稳定的大型水体环境中才能形成，而非仅仅是局部和短暂的融水现象。这项研究不仅提供了火星北部平原曾存在古代海洋的关键地下证据，还揭示了火星曾经经历过长期温暖湿润的气候期，这意味着火星曾长期维持适宜液态水存在的温度和气压条件，远超之前估计的短期融水事件。此外，研究发现的海岸线沉积物电介质特性与地球上由细砂和中砂颗粒的介电常数一致，这进一步证实了其海洋沉积物的性质。
此次发现的最大意义，在于将火星液态水的证据从人迹罕至的极地，扩展到了更适合人类活动的中低纬度地区。如果这里曾存在海洋，那么随着气候变迁，大量水分可能以地下冰的形式被封存，为未来火星基地的水资源利用提供了可能。与极地区域相比，中低纬度地区光照和温度条件更适宜人类活动，如果能够接近这些古海洋区域的地下水资源，将大大降低火星基地的建设和维护成本。此外，这些古海洋沉积物保存了火星气候变化的历史记录，可以帮助人们理解火星如何从温暖湿润转变为寒冷干燥，进而指导人类如何改造火星环境，实现火星的长期可持续居住。