Volcanism on Io: Implications for a Subsurface Magma Ocean


Abstract

  • Jupiter's moon Io is the most volcanically active body in the Solar System, with a mean surface heat flux that is 20 times larger than on the Earth. However, unlike the Earth, extreme volcanism on Io is primarily due to the dissipation of tidal energy and not from radiogenic sources. This study uses the first 1:15,000,000-scale global geologic map of Io to examine the spatial distribution of its volcanic systems and test a range of tidal dissipation models. Results show that clusters of volcanic centers exhibit a statistically significant 30-60° eastward offset relative to the patterns of volcanism predicted by currently favored tidal dissipation models. These models assume that interior heating within Io occurs primarily in the asthenosphere due to the deformation of solid mantle material. However, the observed offset between volcanism and predicted surface heat flux maxima, raises the possibility that there is a missing component in our understanding of melt production and/or magma ascent within Io. One such factor may involve the excitation of fluid tides within a subsurface "magma ocean" (i.e., an extensive region of interconnected silicate partial melt). The existence of Io's magma ocean is supported by recent re-examination of Galileo magnetometer data, which provides evidence of an electromagnetic field induced within a globally continuous magma layer with at least 20% partial melt and 50 km thickness. If so, fluid tidal dissipation may help to explain Io's observed patterns of volcanism and provide a new insight into the moon's interior structure.