Abstract
Permanently magnetic Ganymede carves a distinct magnetosphere inside
Jupiter’s larger magnetic domain, confined by ambient Jovian plasma and
magnetic field along the upstream magnetopause. As Ganymede traverses
the Jovian plasma sheet, ambient magnetoplasma conditions vary at
half-synodic period (5.27 hr), leading to same-period oscillation in the
Chapman-Ferraro (C-F) magnetic field produced by the magnetopause. We
assess the C-F magnetic field as a unique excitation source for
Ganymede’s subsurface ocean. The magnetopause field is shown to diffuse
into but not through the ocean, causing magnetic induction provided the
liquid layer thickness is >~30 km. Then
using an analytical model, we calculate maximum variation of the C-F
field and estimate ~1-10 nT inductive response from the
ocean subjected to the magnetopause’s movement, a range detectable by
the JUpiter ICy moon Explorer (JUICE) spacecraft. Hence, Ganymede’s
magnetopause may become a viable tool for future induction-based study
of the moon’s subsurface ocean.