Io experiences tidal deformation due to its eccentric orbit around Jupiter, which provides a primary energy source for Io’s ongoing volcanic activity and infrared emission¹. The amount of tidal energy dissipated within Io is enormous and has been hypothesized to support the large-scale melting of Io’s interior and the formation of a global subsurface magma ocean. If Io has a shallow global magma ocean, its tidal deformation would be much larger than in the case of a more rigid, mostly solid interior². Here we report the measurement of Io’s tidal deformation, quantified by the gravitational tidal Love number k₂, enabled by two recent flybys of the Juno spacecraft. By combining Juno^3,4 and Galileo^5-7 Doppler data from the Deep Space Network and astrometric observations, we recover Re(k₂) of 0.125±0.047 (1σ) and the tidal dissipation parameter Q of 11.4±3.6 (1σ). These measurements confirm that a shallow global magma ocean in Io does not exist and are consistent with Io having a mostly solid mantle². Our results indicate that tidal forces do not universally create global magma oceans, which may be prevented from forming due to rapid melt ascent, intrusion, and eruption^8,9, so even strong tidal heating – like that expected on several known exoplanets and super-Earths¹⁰ – may not guarantee the formation of magma oceans on moons or planetary bodies.

木卫一由于其围绕木星的偏心轨道而发生潮汐变形，这为木卫一持续的火山活动和红外发射提供了主要能源¹。木卫一内部耗散的潮汐能是巨大的，据推测，它支持木卫一内部的大规模熔化和全球地下岩浆海洋的形成。如果木卫一有一个较浅的全球岩浆海洋，它的潮汐变形将比更坚硬、大部分是固体的内部的情况大得多²。在这里，我们报告了木卫一潮汐变形的测量，由引力潮汐数字 Love 数 _{k 2} 量化，这是由朱诺号宇宙飞船最近两次飞越实现的。通过结合来自深空网络和天体测量观测的朱诺^3,4 和伽利略^5-7 多普勒数据，我们恢复了 0.125±0.047 （1σ） 的 Re（k₂） 和 11.4±3.6 （1σ） 的潮汐耗散参数 Q。这些测量证实了木卫一中不存在全球浅层岩浆海洋，并且与木卫一具有大部分固体地幔一致²。我们的结果表明，潮汐力并不普遍地形成全球岩浆海洋，由于快速熔化上升、侵入和喷发，可能会阻止岩浆海洋^{的形成 8,9}，因此，即使是强烈的潮汐加热——就像在几颗已知的系外行星和超级地球上所预期的那样¹⁰ ——也不能保证在卫星或行星体上形成岩浆海洋。