Magnetic field of Jupiter and the volcanism and rotation of the Galilean satellites

Abstract

The discovery by Voyager 1 of several active volcanoes on Io^1,2 opens up a new approach to problems such as the nature and consequences of volcanism on the celestial bodies. In the past 50 yr only Vsekhsviatsky has actively considered modern volcanism on planets, in particular on Moon-like bodies^3,4. He proceeded from the concept of eruptive origin of comets, however, and did not suggest a physical mechanism to explain the volcanic activity he had postulated. The absence of modern volcanism on the Moon and Mars was against Vsekhsviatsky's ideas and few people considered them seriously, especially in connection with the possible volcanic ejection of icy blocks. Progress was made by Peale et al.⁵ who predicted the existence of the volcanoes just before they were discovered, and suggested a physical mechanism for the volcanism on Io. They suggested that the tidal dissipation caused by the orbit eccentricity could produce a power WM_tid ≈ 1.6 × 10¹² W in Io and 8 × 10¹⁰W in Europa. If the satellites are nonhomogeneous and have a molten interior, the energy release can increase several times. Peal et al. estimated the thickness of Io's solid crust as only 18km. However, “how can Io's south polar region support what appear to be toweling mountains? (ref. 6)”. (The typical relief is ∼10km here²). Also, the lack of a detectable intrinsic magnetic field of Io⁸ does not favour a fully molten interior. I have previously pointed out that Io's and Europe's orbiting in the strong magnetic field of Jupiter may cause their volcanic activity⁷ and this can be confirmed by simple calculations^8,9. Here I shall estimate the energetics in more detail and discuss some peculiarities of the volcanism itself and consequences of the electromagnetic action mainly on the rocky satellites (the ‘icy’ volcanism will be considered elsewhere)