The surfaces of icy moons are covered by fractures, other tectonic features, and active or ancient remains of cryovolcanism. These observations suggest active or recent tectonics, but there is still much unknown about the specific conditions surrounding the formation of these features. One important process leading to the fracture of the ice shell is the freezing and consequent pressurization of its ocean, because water expands upon freezing. However, the influence of dissolved non‐condensable gases (herein referred to as volatiles) on the aforementioned dynamics remains poorly constrained. In this study, we present a new experimental investigation to explore the effect of dissolved volatiles in the internal pressure evolution of 10 cm diameter water spheres subjected to freezing temperatures between ~−60°C and ~−20°C. Our experiments reveal that spheres with a reduced initial amount of volatiles dissolved undergo an abrupt transition with dramatic increase of (a) the time between consecutive ice shell fractures and (b) the pressure required to break the shell. We show from a simple numerical model that this transition occurs when exsolution (i.e., nucleation and growth of bubbles) occurs and the fluid inside the shell becomes significantly more compressible. Exsolution is, in turn, triggered by the gradual thickening of the ice shell, which increases the concentration of dissolved volatiles and eventually leads to saturation. These results suggest that the content of volatiles of icy satellites plays a significant role in their geologic history and potential for habitability.

中文翻译：

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溶解气体对海洋世界冰冻动力学影响的实验研究

冰月卫星的表面覆盖着裂缝，其他构造特征以及活跃的或古老的冰冷火山遗迹。这些观察结果表明构造是活跃的或近来的构造，但围绕这些特征形成的具体条件仍然未知。导致冰壳破裂的一个重要过程是冰层的冻结以及随之而来的海洋增压，因为水在冻结时会膨胀。但是，溶解的不可凝气体（在本文中称为挥发物）对上述动力学的影响仍然难以控制。在这项研究中，我们提出了一项新的实验研究，以探索溶解的挥发物在10°C到〜-20°C的冷冻温度下对10 cm直径水球内部压力演变的影响。我们的实验表明，最初溶解的挥发物含量降低的球体会经历突然的转变，其急剧增加（a）连续的冰壳破裂之间的时间和（b）破坏壳所需的压力。我们从一个简单的数值模型中得出，这种过渡发生在析出（即气泡的成核和生长）发生并且壳内的流体变得可压缩得多时。反过来，冰壳逐渐变厚会触发溶解，这会增加溶解的挥发物的浓度，并最终导致饱和。这些结果表明，冰卫星的挥发物含量在其地质历史和可居住性方面起着重要作用。