Passive radar investigations of Io using Jupiter’s radio emissions as a source for echo detection

Abstract:

Recent work has proposed a Passive Radar Io Magma Explorer (PRIME) as a low-resource approach to perform radar sounding of Io’s subsurface on the sub-Jovian side. Using Jupiter’s radio emissions as its source for echo detection, an onboard passive receiver would correlate the incoming direct and reflected surface and subsurface signals to investigate the physical state of Io, its crustal thickness, and the presence of shallow magma reservoirs and global magma ocean. Here, we assess the potential for passive sounding using Jupiter’s decametric radiation to investigate the subsurface of Io. We provide a detailed analysis of the expected link budget for a passive sounder on a flyby mission, and we characterize Jupiter as a radio source for passive sounding in terms of burst frequency, burst intensity, and illumination opportunities at Io. We then project the performance of the passive technique by estimating the signal-to-noise ratio of the subsurface reflection and maximum penetration depth as a function of various crustal parameters and center frequencies in the MHz range. Our modeling results suggest that passive sounding could perform up to depths of 10 km for subsurface materials with low loss tangents and a wide range of possible mantle permittivity values. While subsurface materials with extremely high loss tangents present a challenge and would limit the penetration depths to 1-3 km, passive sounding could still examine Io’s near subsurface and crustal properties. Operating with reduced size, mass, and power consumption, a receive-only approach using Jupiter’s radio emissions therefore has the potential to provide a low-resource survey of Io’s crustal structure.