The Stability of a Dense Crust Situated on Small Bodies

IF 3.8 Q2 ASTRONOMY & ASTROPHYSICS The Planetary Science Journal Pub Date : 2024-08-30 DOI:10.3847/psj/ad65d2
Yoshinori Miyazaki, David J. Stevenson
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Abstract

Small planetary bodies in the solar system, including Io, Ganymede, and Callisto, may have a crust denser than their underlying mantle. Despite the inherent gravitational instability of such structures, we show that the growth timescale of the Rayleigh–Taylor (RT) instability can be as long as the age of the solar system, owing to the strong temperature dependence of viscosity. Even in cases where the instability timescale is shorter, the instability is confined to a thin layer at the base of the crust, making the foundering of the entire crust improbable in many scenarios. This study delineates the onset and aftermath of the RT instability, applying a quantitative framework to assess the stability of (i) rock-contaminated crust on icy satellites, and (ii) silicate crust floating on top of a subsurface magma ocean on Io. Notably, for Io the RT instability peels off only 10–100 m from the crust’s base, and thermal diffusion rapidly recovers the crustal thickness through solidification of a magma ocean. Despite recurrent delamination of the crustal base, the initial crustal thickness is maintained by thermal diffusion, virtually stabilizing a floating dense crust. Cracking of the crust also is unlikely to result in the foundering of the crust. A dense crust on a small body is therefore difficult to be overturned, suggesting the potential ubiquity of dense surface layers throughout the solar system.
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小天体上致密地壳的稳定性
太阳系中的小型行星体,包括木卫一、木卫三和卡利斯托,可能具有比其下层地幔密度更高的地壳。尽管这类结构具有固有的引力不稳定性,但我们的研究表明,由于粘度与温度密切相关,瑞利-泰勒(RT)不稳定性的增长时间尺度可能与太阳系的年龄一样长。即使在不稳定性时间尺度较短的情况下,不稳定性也仅限于地壳底部的薄层,因此在许多情况下不可能发生整个地壳的崩塌。本研究描述了 RT 不稳定性的起始和后果,应用定量框架评估了 (i) 冰卫星上受岩石污染的地壳和 (ii) 浮在木卫二地表下岩浆海洋顶部的硅酸盐地壳的稳定性。值得注意的是,木卫二的 RT 不稳定性仅在距离地壳底部 10-100 米处剥离,热扩散通过岩浆洋的凝固迅速恢复了地壳厚度。尽管地壳底部反复分层,但最初的地壳厚度通过热扩散得以保持,实际上稳定了浮动致密地壳。地壳开裂也不太可能导致地壳崩塌。因此,小天体上的致密地壳很难被推翻,这表明致密表层在太阳系中可能无处不在。
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来源期刊
The Planetary Science Journal
The Planetary Science Journal Earth and Planetary Sciences-Geophysics
CiteScore
5.20
自引率
0.00%
发文量
249
审稿时长
15 weeks
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