自洽演化模型显示木星和土星中双扩散混合较弱
Self-Consistent Evolution Models Show Weak Double-Diffusive Mixing in Jupiter and Saturn
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中文总结 AI 辅助
研究巨行星‘模糊’核中双扩散对流重元素再分布效率，在行星演化代码中实现跨对流阶梯输运方法并应用于木星和土星模型，发现双扩散对流混合有限，重元素分布可能需其他机制。
中文摘要 AI 辅助
巨行星‘模糊’核中的双扩散对流作为重元素重新分布机制被广泛讨论，但其在演化模型中的效率仍不确定。以往估计依赖理想化成分结构，未在行星演化计算中自洽处理双扩散输运。本文在行星演化代码\texttt{APPLE}中实现跨对流阶梯的输运方法并应用于木星和土星的形成后内部模型。这些模型经过45.6亿年的对流、扩散和双扩散输运演化。我们发现双扩散对流在深层内部和包层之间产生的混合有限。在木星和土星中，在整个冷却历史中重新分布的重物质不到约1个地球质量，原始成分梯度基本保持不变。这种低效率的产生是因为驱动成分输运的浮力功受到深层内部热能预算的限制，这与在更有利于层合并和有效混合的区域运行的理想化布辛涅斯克模拟形成对比。因此，仅双扩散对流不能显著侵蚀形成过程中产生的成分梯度。木星和土星中观测到的重元素分布因此可能需要额外的输运机制或形成途径，包括大型碰撞事件，这些事件产生的初始混合比标准吸积模型预测的更广泛。
英文摘要
Double-diffusive convection in the ``fuzzy'' cores of giant planets has been widely discussed as a mechanism for redistributing heavy elements, but its efficiency in evolutionary models remains uncertain. Previous estimates rely on idealized compositional structures and have not treated double-diffusive transport self-consistently in planetary evolution calculations. Here we implement a prescription for transport across convective staircases in the planetary evolution code \texttt{APPLE} and apply it to post-formation interior models of Jupiter and Saturn containing compositional gradients produced during formation. These models are evolved for 4.56 Gyr including convection, diffusion, and double-diffusive transport. We find that double-diffusive convection produces limited mixing between the deep interior and the envelope. In both Jupiter and Saturn, less than $\sim 1\,M_\oplus$ of heavy material is redistributed over the full cooling history, leaving the primordial compositional gradients largely intact. This inefficiency arises because the buoyancy work available to drive compositional transport is constrained by the thermal energy budget of the deep interior, in contrast to idealized Boussinesq simulations that operate in regimes more favorable to layer merging and efficient mixing. As a result, double-diffusive convection alone cannot significantly erode the compositional gradients generated during formation. The observed heavy-element distributions in Jupiter and Saturn therefore likely require additional transport mechanisms or formation pathways, including large collisional events, that produce broader initial mixing than standard accretion models predict.
发表机构
- California Institute of Technology（加州理工学院）
- University of California, Los Angeles（加州大学洛杉矶分校）
- University of California, Santa Cruz（加州大学圣克鲁兹分校）
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