arXiv 2407.093412024-07astro-ph.EP

具有原始成分梯度的气态巨行星中的对流混合

Convective Mixing in Gas Giant Planets with Primordial Composition Gradients

Henrik Knierim, Ravit Helled

备注：: published in ApJ, 12 pages, including 10 figures, plus 4 pages appendix; v4 follows the ApJ language guidelines
发表信息：: ApJ 977:227 (2024)
DOI：: 10.3847/1538-4357/ad8dd0

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AI总结：

本研究模拟巨行星演化，发现对流混合效率受初始熵控制，低熵下成分梯度可长期存在，并提出了预测混合的解析模型，强调大气成分未必代表整体成分。

摘要：

将大气测量与行星整体成分乃至最终的行星起源联系起来，是行星科学的一个关键目标。在本工作中，我们识别了大气成分代表整体成分的情形。我们模拟了巨行星的演化，考虑了广泛的行星质量范围（$0.3-2~M_{\mathrm{J}}$）、初始熵范围（$8-11~k_{\mathrm{B}} m_\mathrm{u}^{-1}$）以及原始重元素剖面。我们发现，对流混合在早期（年龄 $\lesssim 10^7$ 年）最为高效，且原始成分梯度可能被侵蚀。然而，在若干情形下，大气成分可能与行星整体成分存在很大差异，具体结果取决于细节。我们表明，对流的效率主要由底层熵剖面控制：对于 $8-9~k_\mathrm{B} m_\mathrm{u}^{-1}$ 的低初始熵，对流混合可能受到抑制，成分梯度可持续数十亿年。混合效率随质量的标度关系由原始熵决定。对于相同的原始熵，低质量行星比高质量行星混合得更高效。然而，如果原始内部熵随质量增加，这一趋势可能反转。我们还提出了一个新的解析模型，用于预测在存在成分（和熵）梯度情况下的对流混合。我们的结果强调了大气丰度测量解释的复杂性，并表明迫切需要更好地理解行星形成过程，因为它在决定行星演化和最终结构中起着关键作用。

英文摘要：

Linking atmospheric measurements to the bulk planetary composition and ultimately the planetary origin is a key objective in planetary science. In this work, we identify the cases in which the atmospheric composition represents the bulk composition. We simulate the evolution of giant planets considering a wide range of planetary masses ($0.3-2~M_{\mathrm{J}}$), initial entropies ($8-11~k_{\mathrm{B}} m_\mathrm{u}^{-1}$), and primordial heavy-element profiles. We find that convective mixing is most efficient at early times (ages $\lesssim 10^7$ yr) and that primordial composition gradients can be eroded. In several cases, however, the atmospheric composition can differ widely from the planetary bulk composition, with the exact outcome depending on the details. We show that the efficiency of convection is primarily controlled by the underlying entropy profile: For low primordial entropies of $8-9~k_\mathrm{B} m_\mathrm{u}^{-1}$, convective mixing can be inhibited and composition gradients can persist over billions of years. The scaling of mixing efficiency with mass is governed by the primordial entropy. For the same primordial entropy, low-mass planets mix more efficiently than high-mass planets. If the primordial internal entropy would increase with mass, however, this trend could reverse. We also present a new analytical model that predicts convective mixing under the existence of composition (and entropy) gradients. Our results emphasize the complexity in the interpretation of atmospheric abundance measurements and show the great need to better understand the planetary formation process as it plays a key role in determining the planetary evolution and final structure.

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