How Enceladus’ plume depends on the crevasse wall temperature: An experimental perspective

In this study, plume experiments were conducted to mimic the thermodynamic conditions on Saturn’s moon, Enceladus. The icy moon’s subsurface ocean and cracks in the surface have been simulated using a liquid water reservoir and a narrow channel, while the low-pressure environment at Enceladus’ surface was achieved with a vacuum chamber. We aimed to examine how channel temperature affected the plume’s temperature, solid fraction and velocity, testing two models with differing wall temperatures: room temperature and near 0 °C. The colder setup better replicated Enceladus’ plume, producing a saturated flow in which nucleation of icy particles is possible. A conservative 1.5%–3% minimum solid fraction is estimated from measurements and modelling. Pitot-tube measurements indicated velocities around 400–500 m/s at the channel outlet . Flow temperature and velocity are closely correlated with wall temperature, indicating effective heat transfer. With a plume model based on the energy conservation law, we concluded that supersonic plume velocities observed on Enceladus cannot be achieved with straight channels, i.e. without requiring extreme expansion ratios. Additionally, the research provides evidence of the relationship between the crevasse’s expansion ratio and the temperatures of flow and crevasse walls. • Enceladus, and icy moon of Saturn, posses an ocean under its icy crust, which escapes via crevasses though large plume of water gas and icy particles. • We developed laboratory experiments to simulate this plume and found that the temperature of the crevasse walls strongly influences plume temperature, velocity, and solid fraction. • Only when the channel walls are cold can nucleation of icy grains occur, yielding a minimum solid fraction of 1.5%–3%. • Furthermore, our results show that supersonic velocities—as observed on Enceladus— require extreme expansion ratios, which are not achievable in straight channels.