The Interior of Enceladus

Titan's gravity field and interior structure after Cassini

“…Adopting a simple two-layer model (rocky core, H 2 O mantle), taking the moment of inertia factor to be 0.341, and assuming the average density across the H 2 O layers is 1000 kg/m 3 , the known radius (2575 km) and bulk density (1881 kg/m 3 ) can be used to solve for the core radius and density (e.g., see eqs. 1 and 2 in Hemingway, et al, 2018). Under these assumptions, we obtain an H 2 O layer thickness of ~400 km, leaving a large rocky core with a density around 2500 kg/m 3 .…”

“…As with the gravitational potential, we compute the hydrostatic equilibrium figures, shown along the dashed line in Figure 4b for various moments of inertia, again using the Radau-Darwin relation (e.g., see eqs. 18, 21-23 in Hemingway, et al, 2018). Whereas Figure 6b shows the Corlies, et al (2017) topography with respect to a reference sphere, with radius 2575 km, Figure 6d shows the topography with respect to the hydrostatic equilibrium figure expected for an assumed momen t of inertia factor of 0.341.…”

“…The moment of inertia values indicated along the dashed line in Figure 4a can be computed via the Radau-Darwin equation (Darwin, 1899;Murray and Dermott, 1999), which relates the moment of inertia factor to the fluid Love number k 2f , which can in turn be related to J 2 and C 22 (e.g., see eqs. 16, 21-23 in Hemingway, et al, 2018). If Titan were perfectly hydrostatic, one could thus obtain k 2f , and therefore the moment of inertia factor, directly from either of the 2 obs or 22 obs terms, where the superscript 'obs' refers to the observed values ( Table 2).…”

Key Technologies and Instrumentation for Subsurface Exploration of Ocean Worlds

“…For Enceladus, the lower and upper limits of the average ice shell thickness are 18 km and 44 km, respectively (Fig. 2) (Hemingway et al 2018). Although most authors now agree that the ice shell is thinnest at the poles and thickest at the equator, the exact numbers are still a matter of debate.…”

“…From the considerations above, it seems well possible that liquid water is situated at a depth of only a few hundred meters inside the tiger-stripe fractures. The width of the water filled part of the cracks is unknown but from several models it is Ice-shell thickness at Enceladus (assuming complete Airy compensation of all known topography), ranging from ≈ 6 km at the south pole to ≈ 36 km at the equator, with a mean thickness of 22 km (adapted from Hemingway et al (2018)) estimated to be in the order of 1 m (Kite and Rubin 2016;Spencer et al 2018). The exact depth of the water table is probably variable due to "flushing" from tidal flexing of the crust and can vary by tens of meters (Kite and Rubin 2016).…”