Controlled boiling on Enceladus: Model of the vapor-driven jets

Abstract:

Plumes of water vapor and ice particles have been observed from the cracks, the so-called tiger stripes, at the south polar region of the Saturn's satellite Enceladus. The observed high salinity (~ 1%) of the ice particles in the plumes may indicate that the plumes originate from a subsurface liquid ocean. Additionally, intense thermal radiation has been observed near the tiger stripes (within tens of meters). This could indicate that the radiation is associated with the plumes’ activitity, but the connection has not been studied in detail. Here, we investigate whether plumes originating from a subsurface liquid ocean can explain the observed vapor mass flux and heat flow. We investigate the fluid dynamics of the flow in the crack as well as interactions between the flow and ice walls. As the flow rises within the crack, some water vapor condenses on to the ice walls and releases latent heat. This heat is conducted through the ice and is eventually emitted to space by thermal radiation. The rest of the flow reaches the surface and is emitted to space as plumes. Furthermore, we consider the possibility that the total length of the cracks can be larger than that of the tiger stripes. We find that our model could explain the observed vapor mass flux and heat flow if the crack width is 0.05-0.075 m and each tiger stripe has ~1.7 fractures on average (the total length of the crack is 1.7× 500 km). The observed intense heat flow near the tiger stripes can be explained by latent heat release through vapor sublimation from the flow to the ice walls near the surface. Additionally, we find that if the flow contains 5-10 % of ice particles at the bottom of the flow (at the liquid-vapor interface), the ice to vapor ratio near the surface could reach 10-30 %. We find that the total mass flux of the plumes becomes larger when the crack width is larger, which is consistent with the observation that the plume mass flux increases near the apocenter where the crack width is expected to be largest. We discuss conditions to maintain the liquid subsurface ocean in our companion presentation (Ingersoll & Nakajima, 2015 AGU).