Cascading parallel fractures on Enceladus

Abstract

Active eruptions from the south polar region of Saturn's small (~500 km diameter) moon Enceladus are concentrated along a series of lineaments known as the `tiger stripes', thought to be partially open fissures that connect to the liquid water ocean beneath the ice shell. Whereas aspects of the tiger stripes have been addressed in previous work, no study to date simultaneously explains why they should be located only at the south pole, why there are multiple approximately parallel and regularly spaced fractures, and what accounts for their spacing of ~35 km. Here we propose that secular cooling and the resulting ice shell thickening and global tensile stresses cause the first fracture to form at one of the poles, where the ice shell is thinnest due to tidal heating. The tensile stresses are thereby partially relieved, preventing a similar failure at the opposite pole. We propose that subsequent activity then concentrates in the vicinity of the first fracture as the steadily erupted water ice loads the flanks of the open fissure, causing bending in the surrounding elastic plate and further tensile failure in bands parallel to the first fracture, leading to a cascading sequence of parallel fissures until the conditions no longer permit through-going fractures.