The melt zone in the volcanically active satellite Io plays a key role in diverse processes such as volcanism, heat transfer, tidal dissipation, and the orbital evolution of the Galilean satellites in the Laplace resonance. Information on the melt distribution, the degree of partial melt, and the possible existence of a global magma ocean has been derived from Galileo magnetic induction measurements, volcanic eruption temperatures, and Hubble Space Telescope auroral spot observations but is currently inconclusive. Here, we calculate the libration amplitude of Io for a diverse set of internal structure models and show that Io's libration can provide insight into the existence of a global magma ocean and into the thickness and rigidity of the crust above it. The diurnal libration amplitude of Io is several times larger if Io has a magma ocean instead of a partial melt asthenosphere and can reach values of above 1 km, making it easily observable for spacecraft flying close by Io on multiple occasions. It also strongly increases with decreasing crustal thickness and increases significantly with increasing rigidity. We demonstrate that the combination of observations of the libration amplitude and the tidal Love number k₂ will allow estimating the rigidity and thickness of the crust separately, which is impossible with only one of the quantities observed.

中文翻译：

---

艾欧的图书馆，潮汐和内部结构

火山活动卫星Io中的融化带在诸如火山作用，传热，潮汐消散以及在拉普拉斯共振中的伽利略卫星的轨道演化等各种过程中起着关键作用。有关熔融物分布，部分熔融程度以及可能存在的全球岩浆海洋的信息已从伽利略磁感应测量，火山喷发温度和哈勃太空望远镜的极光点观测中得出，但目前尚无定论。在这里，我们为一组不同的内部结构模型计算了Io的释放幅度，并表明Io的释放可以提供对全球岩浆海洋的存在以及其上方地壳厚度和刚度的洞察力。如果Io有岩浆海洋而不是部分融化的软流圈，则Io的日释放幅度会大几倍，并且可以达到1 km以上的值，这使得它很容易观察到Io多次飞行。它也随着地壳厚度的减小而强烈增加，并随着刚性的增加而显着增加。我们证明了解放幅度和潮汐洛夫数的观察结果的结合k ₂将允许分别估计地壳的刚度和厚度，这仅是观察到的量之一是不可能的。