Dynamics signatures of water-filled faults in Enceladus’s plume activity

The remarkable geysers of Enceladus, emanating from the faults in its southern polar region, offer a unique chance to sample the internal ocean and may provide insight into the dynamic processes within the faults. The observed activity measured by the plume’s brightness exhibits strong temporal variations on different time scales. The most prominent is the diurnal time scale, which indicates tidal stress modulation of the activity [1-3]. However, none of the mechanisms that have been suggested so far does self-consistently explain the key aspects of the activity, including the timing of the peak at mean anomaly MA=200deg and the presence of the secondary peak at MA=40deg. To describe the activity characteristics, we combine a global model of eccentricity-driven tidal deformation of the Enceladus ice shell, including frictional faults [4], with a model of vapor transport [5] and water table movement [6] in the faults. We offer a comprehensive explanation of the observed plume activity by combining the shear-modulated mechanism with the previously considered normal-stress-modulated fault aperture near the surface. Our activity model based on the two mechanisms explains the presence, timing, and relative magnitude of the two peaks of plume activity for low friction coefficients. By considering different capacities of the two mechanisms to carry vapor and various types of solid grains, our model can explain moderate fluctuations in vapor mass flux [7] over the orbital period compared to the variations in plume brightness. Similarly, we predict possible temporal variations of the Type II and Type III particles in the jets [8].

This research was supported by Czech Science Foundation (project no. 22-20388S)

REFERENCES:

[1] Hedman et al. (2013), Nature 500, 182-184.

[2] Nimmo et al. (2014), Astron. J. 148(3), 46.

[3] Ingersoll et al. (2020), Icarus 344,113345.

[4] Pleiner Sládková et al. (2021). GRL 48(19), e2021GL094849.

[5] Ingersoll&Nakajima (2016), Icarus 272, 309-318.

[6] Kite&Rubin (2016), PNAS 113 (15), 3972-3975.

[7] Hansen et al (2020), Icarus 344, 113461.

[8] Postberg et al. (2018), Nature 558, 564–568.