Cryovolcanism inside out: Signatures of past and present cryovolcanism on Europa

Introduction. Europa, the most visibly active icy moon of Jupiter, is a prime target for the search for life in the outer solar system. Two spacecraft missions, Europa Clipper from the National Aeronautics and Space Administration (NASA) and the Jupiter Icy Moon Explorer (JUICE) from the European Space Agency (ESA), will conduct extensive observations of its surface, gravity field and environment starting 2030. It has been proposed that liquid briny water reservoirs could be injected and stored in Europa’s ice shell, causing the formation of various geological features. In particular, these reservoirs could occasionally trigger eruptions [1], resulting in flows on the surface and vapor plumes in the atmosphere.

If shallow liquid brine reservoirs are indeed present in Europa's ice shell, they would leave surface evidence that future missions could detect, including local thermal anomalies, ice shell thickness change, and erupted briny solutions with time varying salinity. We present a novel simulation that models thermal, physical, and compositional ice shell and reservoir evolution and eruption, and that predicts the various signatures detectable by future robotic exploration.

Cryomagma chemistry. We conserve enthalpy to solve the coupled chemical evolution and pressurization of freezing brines stored in Europa’s ice shell using current best estimates of the oceanic composition [2] to predict the composition of erupted cryolava. This composition varies with time, as salts concentrate during freezing [3], which could lead to erupted brines of varying composition depending on the reservoir frozen fraction when the eruption is triggered. The equilibrium freezing of oceanic brines is modeled using the software PHREEQC to obtain the liquid and solid fraction of each component of the aqueous solution as a function of the temperature. 

Ice shell and reservoir modelling. We simultaneously model the ice shell and reservoir thermal, physical, and compositional evolution self-consistently building upon the framework of [4]. We solve for the conservation of enthalpy using conservative finite differences in a one-dimensional (1D) spherical shell, propagated explicitly forward in time. The thermophysical properties of the multiphase model are temperature-, pressure-, and composition dependant, thus the composition and physical state are consistently updated at every time step. Finally, modeled eruption frequency and eruptive characteristics are dependent on the properties and their gradients in ice surrounding the reservoir.

Results. Outputs of the model include the temporal evolution of the temperature in the ice shell, reservoir, and at the surface, and the time of eruptions and erupted cryomagma composition (Fig. 1).

Figure 1: Temporal evolution of signatures of a 1 km thick cryomagma reservoir located 1 km bellow the surface.

Acknowledgements. Portions of this research were carried out at the Jet  Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration (NASA). This work was supported by NASA’s Solar System Workings program (grants #80NM0018F0612 and #80NSSC20K0139)

References. [1] Lesage et al. (2022) PSJ 3(7), 170, [2] Melwani Daswani et al. (2021) GRL 48(18), [3] Naseem et al. (2023) PSJ 4(9), 181, [4] Howell, S. M. (2021) PSJ 2(4), 129.