Two major hypotheses have been proposed for the origin of the Martian moons Phobos and Deimos: the in situ formation theory, supported by the fact that they have circular orbits nearly parallel to the Martian equator, and the asteroid capture theory, supported by the similarity of their reflectance spectra to those of carbonaceous asteroids. Regarding the in situ formation theory, recent theoretical studies have focused on the huge impact scenario, which proposes that debris ejected into orbits during the formation of a giant impact basin on Mars accumulated to form the Martian moons. On the other hand, gas drag from a Martian gas envelope composed of gravitationally attracted solar nebula gas has been proposed as a mechanism for trapping the approaching asteroidal objects in areocentric orbits. In particular, an object entering a temporarily captured orbit in the Martian gravitational sphere would easily evolve into a fully captured moon with a near-equatorial orbit under realistic gas densities. The upcoming Phobos sample return mission is expected to elucidate the origin of both moons, with implications for material transport in the early Solar System and the early evolution of Mars. ▪ The origin of Mars’ small moons, Phobos and Deimos, has long been an open question. ▪ The leading hypotheses are asteroid capture, inferred from their appearance like primitive asteroids, and giant impact, implied by the regularity of their orbits. ▪ The origin of Phobos will be precisely determined by a sample return mission to be conducted in the late 2020s to early 2030s. ▪ Determining the origin of the Martian moons will provide clues to clarifying how the parent planet Mars formed and came to have a habitable surface environment.Expected final online publication date for the Annual Review of Earth and Planetary Sciences, Volume 52 is May 2024. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

中文翻译：

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火卫一和火卫二的起源等待直接探索

关于火星卫星火卫一和火卫二的起源，人们提出了两个主要假设：原位形成理论，其支持的事实是它们具有几乎平行于火星赤道的圆形轨道；小行星捕获理论，其支持的相似性是：它们的反射光谱与碳质小行星的反射光谱相似。关于原位形成理论，最近的理论研究集中在巨大撞击情景上，该情景提出，在火星上形成巨大撞击盆地时，喷射到轨道上的碎片积累起来形成了火星卫星。另一方面，来自由引力吸引的太阳星云气体组成的火星气体包层的气体阻力已被提议作为将接近的小行星物体捕获在近心轨道中的机制。特别是，进入火星引力球中临时捕获轨道的物体很容易在现实气体密度下演变成具有近赤道轨道的完全捕获卫星。即将到来的火卫一样本返回任务预计将阐明两颗卫星的起源，对早期太阳系的物质运输和火星的早期演化产生影响。 ▪ 火星小卫星火卫一和火卫二的起源长期以来一直是一个悬而未决的问题。 ▪ 主要的假设是小行星捕获（从它们的外观像原始小行星一样推断）和巨大的撞击（根据其轨道的规律性暗示）。 ▪ 火卫一的起源将通过 2020 年代末至 2030 年代初进行的样本返回任务精确确定。 ▪ 确定火星卫星的起源将为澄清母行星火星如何形成以及如何形成适宜居住的表面环境提供线索。《地球与行星科学年度评论》第 52 卷的预计最终在线出版日期为 2024 年 5 月。有关修订后的估计，请参阅 http://www.annualreviews.org/page/journal/pubdates。