Abstract: The icy moons in the Solar System are of great scientific interest due to their potential subsurface oceans. Single-frequency magnetic induction response is limited in its sensitivity to the depths of conductive layers and often suffers from parameter degeneracy during inversion, making it challenging to uniquely determine the conductivity and thickness of subsurface oceans. The feasibility of the multi-frequency magnetic induction response method in inferring the properties of subsurface oceans in icy moons is investigated, and Jupiter's moon, Europa, is selected as a case study. The induced magnetic field of Europa is first simulated utilizing a specific internal structure model and a time-varying field extracted from Jovian magnetospheric models. Based on multiple sets of simulated data, a multi-start trust-region-reflective optimization method is applied to invert the ocean conductivity and thickness. The effects of noise levels, parameter combinations, and detection conditions (e.g., detection timing and orbital configurations) on the inversion results are also analyzed and discussed. The results indicate that, under high signal-to-noise ratio (SNR), multi-frequency magnetic induction response can effectively reduce the degeneracy between ocean conductivity and thickness. It provides more accurate parameter estimates compared with single-frequency magnetic induction response in a certain parameter space, but further information is still required to determine the unique and reasonable solution. When SNR decreases due to poor detection conditions or large noise, the ability of certain frequencies to constrain parameters is weakened, leading to the reduction of multi-frequency magnetic induction response inversion accuracy.

Key words: icy moons, Europa, induced magnetic field, internal structure, deep space exploration