The origin of the Martian moons, Phobos and Deimos, remains elusive. While the morphology and their cratered surfaces suggest an asteroidal origin^1,2,3, capture has been questioned because of potential dynamical difficulties in achieving the current near-circular, near-equatorial orbits^4,5. To circumvent this, in situ formation models have been proposed as alternatives^6,7,8,9. Yet, explaining the present location of the moons on opposite sides of the synchronous radius, their small sizes and apparent compositional differences with Mars² has proved challenging. Here, we combine geophysical and tidal-evolution modelling of a Mars–satellite system to propose that Phobos and Deimos originated from disintegration of a common progenitor that was possibly formed in situ. We show that tidal dissipation within a Mars–satellite system, enhanced by the physical libration of the satellite, circularizes the post-disrupted eccentric orbits in <2.7 Gyr and makes Phobos descend to its present orbit from its point of origin close to or above the synchronous orbit. Our estimate for Phobos’s maximal tidal lifetime is considerably less than the age of Mars, indicating that it is unlikely to have originated alongside Mars. Deimos initially moved inwards, but never transcended the co-rotation radius because of insufficient eccentricity and therefore insufficient tidal dissipation. Whereas Deimos is very slowly receding from Mars, Phobos will continue to spiral towards and either impact with Mars or become tidally disrupted on reaching the Roche limit in ≲39 Myr.

火星卫星火卫一和火卫二的起源仍然难以捉摸。虽然形态及其陨石坑表面表明小行星起源^{1,2,3 ，但由于在实现当前的近圆形、近赤道轨道4,5}方面存在潜在的动力学困难，因此捕获受到质疑。为了规避这一点，已提出原位形成模型作为替代方案^6,7,8,9。然而，解释了卫星目前位于同步半径两侧的位置、它们的小尺寸以及与火星^{2的明显成分差异}已证明具有挑战性。在这里，我们将火星-卫星系统的地球物理和潮汐演化模型结合起来，提出火卫一和火卫二起源于可能在原地形成的共同祖先的解体。我们展示了火星-卫星系统内的潮汐耗散，由于卫星的物理运动而增强，使破坏后的偏心轨道在 <2.7 Gyr 内循环，并使火卫一从其原点接近或高于同步轨道。我们对火卫一的最大潮汐寿命的估计远小于火星的年龄，这表明它不太可能与火星一起起源。火卫二最初向内移动，但由于离心率不足，因此潮汐耗散不足，从未超过同转半径。≲ 39 迈尔。