Mapping Eruptions on Enceladus

In 2005, Enceladus became the first moon known to spout plumes of water. Now, researchers are reanalyzing six years of data from the Cassini orbiter to learn more about the origin of these plumes.

Plumes on an Icy Moon

Enceladus, the sixth-largest moon of Saturn, is encased in a shell of reflective ice thought to be several miles thick. This icy crust is marred by craters, chaotically crisscrossed terrain, and — most notably — four long, nearly parallel fissures nicknamed tiger stripes.

The Cassini orbiter spied geysers of water ice and vapor bursting through these fissures, powered by the release of tidal stresses from interactions with another of Saturn’s moons, Dione. The plumes provided the first evidence for an ocean of liquid water beneath Enceladus’s surface. There is much still to learn about the plumes, including whether they spray directly from Enceladus’s subsurface ocean or from a network of shallow pools within the icy crust.

Drawing Back the Curtain

To learn more about the behavior of Enceladus’s plumes and the association between the plumes and the fissures, Joseph Spitale (SETI Institute) and collaborators analyzed 15 epochs of plume activity spread across the years 2009–2015. Their goal was to determine which fissure each plume originated from.

Spitale’s team modeled the plumes as “curtains” that emerge from the fissures. This is an improvement upon previous methods that focused on individual narrow plumes or “jets,” requiring the use of multiple images to triangulate the position of each jet.

The team had previously used the curtain method to identify the source fissures of plumes during a few time periods. In this work, they refined their method and expanded their analysis to a broader set of observations.

Fissure Findings

The analysis linked curtains of erupting plumes to fissures that had been digitized by eye. Most locations along the fissures were active in every epoch, and those that were never or infrequently active were located on the outskirts of the fracture system.

Previously, researchers have noted that the plumes on Enceladus vary in intensity by approximately a factor of three. With the finding that only the ends of the fissures ever truly become inactive, it’s unlikely that the change in intensity is due to fissures turning on and off as Enceladus encounters varying levels of tidal stress. Instead, it’s likely that most locations along the fissures are always active, regardless of tidal stress, with tidal stresses controlling the overall intensity of the eruption and the on-off behavior of just the tips of the fissures.

The distribution of fissure activity may hint that the plumes emerge directly from the subsurface ocean. In order for pools within the ice shell to be the source of the plumes, the locations of the pools must vary in a particular way with the thickness of the ice shell, or there must be a single plume-supplying chamber spanning the entire area of the tiger stripes — a configuration seemingly unable to withstand the immense weight of the ice crust.

Citation

“Curtain-Based Maps of Eruptive Activity in Enceladus’s South-Polar Terrain at 15 Cassini Epochs,” Joseph N. Spitale et al 2025 Planet. Sci. J. 6 67. doi:10.3847/PSJ/adb7d7