Center for Relativistic Astrophysics, School of Physics, Georgia Institute of Technology, Atlanta, Georgia.
Department of Physics, University of Idaho, Moscow, Idaho.
Astrobiology. 2020 Jan;20(1):73-90. doi: 10.1089/ast.2018.1932. Epub 2019 Oct 14.
Variations in the axial tilt, or obliquity, of terrestrial planets can affect their climates and therefore their habitability. Kepler-62f is a 1.4 R planet orbiting within the habitable zone of its K2 dwarf host star. We perform N-body simulations that monitor the evolution of obliquity of Kepler-62f for 10-million-year timescales to explore the effects on model assumptions, such as the masses of the Kepler-62 planets and the possibility of outer bodies. Significant obliquity variation occurs when the rotational precession frequency overlaps with one or more of the secular orbital frequencies, but most variations are limited to ≲10°. Moderate variations (∼10-20°) can occur over a broader range of initial obliquities when the relative nodal longitude (ΔΩ) overlaps with the frequency and phase of a given secular mode. However, we find that adding outer gas giants on long-period orbits (∼1000 days) can produce large (∼60°) variations in obliquity if Kepler-62f has a very rapid (4 h) rotation period. The possibility of giant planets on long-period orbits impacts the climate and habitability of Kepler-62f through variations in the latitudinal surface flux, where large variations can occur on million year timescales.
类地行星自转轴倾斜（倾角）的变化会影响其气候，从而影响其可居住性。开普勒-62f 是一颗 1.4R 行星，它在其 K2 矮星主星的宜居带内运行。我们进行了 N 体模拟，以监测开普勒-62f 倾角的演变，模拟时间跨度为 1000 万年，以探索对模型假设的影响，例如开普勒-62 行星的质量以及是否存在外部天体。当自转进动频率与一个或多个长期轨道频率重叠时，倾角会发生显著变化，但大多数变化的幅度限制在 ≲10°以内。当相对节点经度（ΔΩ）与给定长期模式的频率和相位重叠时，倾角会发生中等程度（∼10-20°）的变化，且初始倾角范围更宽。然而，我们发现，如果开普勒-62f 的自转周期非常快（4 小时），则在长周期轨道（约 1000 天）上添加外部气态巨行星会导致倾角发生较大（约 60°）的变化。长周期轨道上巨行星的存在可能性会通过纬度表面通量的变化影响开普勒-62f 的气候和可居住性，这种变化可以在百万年的时间尺度上发生。
