木星の衛星イオの潮汐加熱,内部構造と火山活動

抄録

Nine active volcanic plumes were observed during the Voyager encounter with the Jovian system. Enhanced tidal dissipation induced by Jupiter is a major energy source for it's active volcanism. The energy coming out from lo is estimated to be 1-2 W/m² which amounts to an order of magnitude larger than the terrestrial heat flow. Large part of this heat flow is transferred to the surface by localized hot spot volcanism. Internal structure and thermal evolution of lo is strongly influenced by tidal heating and advective heat transfer associated with volcanic activity. We review current understanding of tidal dissipation, heat flow measurements and heat flow mechanisms, surface morphology, color and spectral studies, and discuss the nature of volcanism and its role on the internal structure and thermal evolution of Io. A major question on the ionian volcanism is whether volcanic eruption material is silicate or sulfur compounds. According to the available data such as surface spectra and existence of high rugged mountains, layered crustal model consisting of massive silicate crust with superficial sulfur-rich outer layer is preferred. A wide variation of volcanic features is manifestations of complex interaction of silicate, sulfur and sulfur dioxide volcanism. Volcanic and tectonic styles of tidally heated body and unique volatile phases of sulfur and sulfur dioxide which control the ionian volcanic processes provide a significant insight for understanding geologic evolution of terrestrial planets.