巨大陨石坑或将揭示火星卫星的起源之谜

科学家通过分析火星卫星火卫一上的斯蒂克尼陨石坑的重力和运动特征，试图解开这颗卫星的起源谜团 1。火卫一是被火星捕获的小行星，还是火星遭受巨大撞击后产生的碎片，这两种假设对应的撞击时间差异巨大 1。若火卫一由火星碰撞碎片形成，撞击发生于约42亿年前；若为被捕获的小行星，撞击则发生于约26亿年前 1。

斯蒂克尼陨石坑直径为9公里，相对于火卫一平均22.2公里的直径而言规模巨大 1。火卫一绕火星一周耗时仅7小时39分钟 1，这使得对其内部结构的深入研究显得尤为关键。日本即将实施的火星卫星探测任务（MMX）计划于2026年末发射，将对火卫一表面进行采样 1。该任务采用的核心采样器可采集深度达2厘米的物质，气动采样器由美国宇航局提供 1，采集的样本预计于2031年中期返回地球 1，有望为解答火卫一起源问题提供关键证据。

Researchers are using gravitational and orbital characteristics of Stickney, a massive crater on Phobos, Mars' larger moon, to investigate a fundamental question about the satellite's genesis—whether it is a captured asteroid or debris from a catastrophic impact on Mars itself 1. The Stickney crater spans 9 kilometers in diameter 1, covering a significant portion of Phobos, which has an average diameter of 22.2 kilometers and completes one orbit around Mars every 7 hours and 39 minutes 1.

The answer to Phobos' origins hinges partly on when a major impact event occurred in the inner solar system 1. If Phobos formed from material ejected during an impact on Mars, that collision would have taken place approximately 4.2 billion years ago 1. Conversely, if Phobos is a captured asteroid, the relevant impact would date to roughly 2.6 billion years ago 1. Japan's upcoming Martian Moons eXploration (MMX) mission is expected to provide crucial evidence to resolve this question, with a planned launch in late 2026 and sample return to Earth by mid-2031 1. The mission's core sampler can collect material from depths of up to 2 centimeters, with an aerosol collector supplied by NASA 1.