Can we use the ocean-induced magnetic field to reconstruct the flow in subsurface oceans on icy moons?

The electromagnetic induction was one of the key methods that were used to detect global subsurface oceans in icy moons, such as Ganymede (Kivelson et al., 2002) and Europa (Khurana et al., 1998), which are satellites of Jupiter. It is expected that heat coming from the moon’s interior drives convective flow within the ocean. To better understand the dynamics of subsurface oceans, the flows within them have been studied in detail over the last decade (e.g., Soderlund et al., 2014; Soderlund, 2019; Cabanes et al., 2024; Kvorka et al., 2025). Possible flow regimes and characteristic flow speeds were estimated using numerical simulations.

 

A conductive fluid that is flowing in the presence of an ambient magnetic field generates a secondary magnetic field. On Earth, this ocean-induced magnetic field (OIMF) is a small signal but it (its tidal part) can be extracted from the satellite measurements. From this perspective, the Juice and Europa Clipper space missions are very promising as they are supposed to provide such data. That were the key motivations for Šachl et al. (2025) and Šachl et al. (2026) to calculate the OIMF generated in the subsurface oceans of Europa and Ganymede, respectively. In this contribution, we present the next step in the outlined hierarchy for exploitation of magnetic field measurements by the interplanetary probes: the synthetic inverse problem. Specifically, we focus on reconstructing the ocean flow using synthetic OIMF data in two test cases. The first test case corresponds to Ganymede, where the OIMF signal may be strong enough to be detected by the Juice spacecraft (Šachl et al., 2026). The second test case corresponds to Europa, although Europa’s OIMF is weak and most likely on the edge of detectability of both the Europa Clipper and the Juice spacecraft (Šachl et al., 2025). In the presented test cases, we successfully reconstructed the ocean flow. However, we also demonstrate that there exist limitations arising from either the fundamental principles of physics or measurement inaccuracies.  For example, we can reconstruct the vertically averaged flow on Ganymede, but we cannot recover the vertical structure of the flow since Ganymede's OIMF is a static signal.

 

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Kvorka, J., Čadek, O., Šachl, L., Velímský, J. (2025). Icarus, 444, 116807. doi: 10.1016/j.icarus.2025.116807.

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Šachl, L., Kvorka, J., Čadek, O.,Velímský, J. (2025). Icarus, 429, 116375, doi:10.1016/j.icarus.2024.116375.

Šachl, L., Kvorka, J., Čadek, O.,Velímský, J.. Manuscript submitted to JGR: Planets.