Layered semi-convection and tides in giant planet interiors II. Tidal dissipation
Layered semi-convection and tides in giant planet interiors II. Tidal dissipation
复制标题
巨行星内部的分层半对流和潮汐 II。
DOI：
10.1051/0004-6361/201833674
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发表时间：
2019
影响因子：
6.5
通讯作者：
André Q
中科院分区：
文献类型：
--
作者：
André Q
最近的朱诺号观测表明，木星中的重元素可能在其气体包层的很大一部分中被稀释，从而在行星的扩展区域提供稳定的成分梯度。这可能会引发分层的半对流，在更普遍的巨行星背景下，这可能解释了土星的光度过剩，并在导致一些热彗星异常大的半径方面发挥了作用。在巨大的行星内部，它可以采取密度阶梯的形式，这是由薄的稳定分层界面分离的对流层。此外，潮汐耗散的效率强烈地依赖于行星的内部结构，目的是研究在层状半对流区域中，由于其他天体的潮汐引力强迫而激发内波时所产生的潮汐耗散（例如巨行星系统中的卫星，或热木星系统中的恒星）。方法我们采用局部笛卡尔模型，背景分层密度分布受到施加的潮汐强迫，我们用数值方法计算粘性和热耗散率。我们考虑两组边界条件在垂直方向：周期性边界和不可穿透的，无应力的边界，在每种情况下，在水平方向的周期性条件。这些模型是适当的研究强迫的短波长潮汐波的分层半对流的区域的一部分，并在一个扩展的信封中包含分层半对流，respectively.ResultsWe发现，潮汐耗散率可以增强分层半对流的区域相比，一个均匀的对流介质，后者对应于通常的假设中采用的巨行星内部模型。特别是，分层半对流区域拥有更丰富的共振，允许增强耗散更广泛的潮汐频率。这些结果的细节显着依赖于分层的半对流regions.ConclusionsLayered半对流的结构特性可能有助于解释在木星和土星，这还没有得到充分的理论解释观测到的高潮汐耗散率。需要进一步的工作来探索这种机制在全球模型中的效率。
ContextRecent Juno observations have suggested that the heavy elements in Jupiter could be diluted throughout a large fraction of its gaseous envelope, providing a stabilising compositional gradient over an extended region of the planet. This could trigger layered semi-convection, which, in the context of giant planets more generally, may explain Saturn’s luminosity excess and play a role in causing the abnormally large radii of some hot Jupiters. In giant planet interiors, it could take the form of density staircases, which are convective layers separated by thin stably stratified interfaces. In addition, the efficiency of tidal dissipation is known to depend strongly on the planetary internal structure.AimsWe aim to study the resulting tidal dissipation when internal waves are excited in a region of layered semi-convection by tidal gravitational forcing due to other bodies (such as moons in giant planet systems, or stars in hot Jupiter systems).MethodsWe adopt a local Cartesian model with a background layered density profile subjected to an imposed tidal forcing, and we compute the viscous and thermal dissipation rates numerically. We consider two sets of boundary conditions in the vertical direction: periodic boundaries and impenetrable, stress-free boundaries, with periodic conditions in the horizontal directions in each case. These models are appropriate for studying the forcing of short-wavelength tidal waves in part of a region of layered semi-convection, and in an extended envelope containing layered semi-convection, respectively.ResultsWe find that the rates of tidal dissipation can be enhanced in a region of layered semi-convection compared to a uniformly convective medium, where the latter corresponds with the usual assumption adopted in giant planet interior models. In particular, a region of layered semi-convection possesses a richer set of resonances, allowing enhanced dissipation for a wider range of tidal frequencies. The details of these results significantly depend on the structural properties of the layered semi-convective regions.ConclusionsLayered semi-convection could contribute towards explaining the high tidal dissipation rates observed in Jupiter and Saturn, which have not yet been fully explained by theory. Further work is required to explore the efficiency of this mechanism in global models.