PerspectivePlanetary Science

Io's Tortured Interior

Science  03 Jun 2011:
Vol. 332, Issue 6034, pp. 1157-1158
DOI: 10.1126/science.1206534

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Jupiter's moon Io is the most volcanic object in the solar system, injecting about a metric ton per second of sulfurous material into Jupiter's magnetic environment. Images and movies from spacecraft have caught Io's volcanoes in the act of erupting since their discovery by Voyager in 1979. This prolific activity hints at a tortured inner structure. On page 1186 of this issue, Khurana et al. (1) report magnetometer data obtained by the Galileo spacecraft and use it to infer the presence of a global magma ocean at least 50 km thick under Io's icy, pock-marked, and colorful surface. This result makes Io stand out as unique among its icy satellite siblings at Jupiter, Saturn, and beyond, where the other subsurface oceans are water-rich. It also confirms the importance of magnetic field and plasma instruments in probing the internal structure of solar system bodies.