潮汐与行星适居性的演化
Tides and the Evolution of Planetary Habitability
摘要：
由主星引力引起的潮汐可以减少行星轨道的半长轴和偏心率。这种效应只适用于轨道非常接近其宿主恒星的行星。低质量恒星的宜居带也很近，潮汐可以改变这些位置行星的轨道。我们计算了低质量恒星周围的假设类地行星的潮汐演化，并表明潮汐可以使行星演化超过宜居带的内边缘，有时不到10亿年。这种迁移需要大偏心率（>0.5）和低质量恒星（<0.35 M_Sun）。这种迁移可能对大气的演化、内部加热和盖亚假说有重要影响。同样，在宜居带内部探测到的行星在过去可能是宜居的。我们考虑了最近发现的~5 M地球行星Gliese 581 c过去的可居住性。我们发现，它可能已经居住的轨道和物理性质的合理选择，最近2 Gyr前。然而，当我们包括来自额外的同伴的约束时，我们看到大多数预测过去可居住性的参数选择需要系统的两个内行星已经越过它们相互的3：1平均运动共振。由于这种交叉可能会导致共振捕获，这是没有观察到的，我们得出结论，Gl 581 c可能永远不适合居住。
英文摘要：
Tides raised on a planet by its host star's gravity can reduce a planet's orbital semi-major axis and eccentricity. This effect is only relevant for planets orbiting very close to their host stars. The habitable zones of low-mass stars are also close-in and tides can alter the orbits of planets in these locations. We calculate the tidal evolution of hypothetical terrestrial planets around low-mass stars and show that tides can evolve planets past the inner edge of the habitable zone, sometimes in less than 1 billion years. This migration requires large eccentricities (>0.5) and low-mass stars (<0.35 M_Sun). Such migration may have important implications for the evolution of the atmosphere, internal heating and the Gaia hypothesis. Similarly, a planet detected interior to the habitable zone could have been habitable in the past. We consider the past habitability of the recently-discovered, ~5 M_Earth planet, Gliese 581 c. We find that it could have been habitable for reasonable choices of orbital and physical properties as recently as 2 Gyr ago. However, when we include constraints derived from the additional companions, we see that most parameter choices that predict past habitability require the two inner planets of the system to have crossed their mutual 3:1 mean motion resonance. As this crossing would likely have resulted in resonance capture, which is not observed, we conclude that Gl 581 c was probably never habitable.
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