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.

中文翻译：

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等待直接探索的火卫一和火卫二的起源


关于火星卫星火卫一和火卫二的起源，已经提出了两个主要的假设：原位形成理论，由它们具有几乎平行于火星赤道的圆形轨道这一事实支持，以及小行星捕获理论，由它们的反射光谱与碳质小行星的反射光谱相似性支持。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期间喷射到轨道上的碎片积累形成火星卫星。另一方面，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一种将接近的小行星物体困在近心轨道上的机制。特别是，进入火星引力球中临时捕获轨道的物体很容易演变成在实际气体密度下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有望阐明这两颗卫星的起源，对太阳系早期的物质运输和火星的早期演化产生影响。▪火星的小卫星火卫一和火卫一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推断，以及巨大的撞击，由它们的轨道的规律性推断出来。▪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阐明母行星火星如何提供线索形成并拥有宜居的地表环境。