Miranda, a satellite of Uranus, appears in Voyager images to have had an active geological history, seemingly characterized by relaxation of very large-scale topography or the sinking of large blocks of material accreted by the satellite, with associated extrusion, eruption, and flow of the icy material on the body1. The low temperature of Miranda (<100K) would preclude such mobilization of water ice. Hypothetical methane or ammonia constituents have been invoked to circumvent the problem2. Here we offer an alternative explanation: topography or anomalous blocks themselves may once have provided the conditions for heating and softening the supporting material, even pure ice, by permitting chaotic rotation of the satellite (J. Wisdom, unpublished lecture). Moreover, this heating mechanism is self-limiting due to rapid damping of the orbital eccentricity. Topography at the presently observed scale (roughly 20km on this 240-km-radius body) could be preserved.
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