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- Title
Poroviscoelastic Gravitational Dynamics.
- Authors
Kamata, S.
- Abstract
Global‐scale periodic deformation has been studied using the (visco)elastic gravitational theory, which assumes a planetary body consists of solid or liquid layers. Recent planetary exploration missions, however, suggest that a global layer of a mixture of solid and liquid exists in several planetary bodies. This study provides a theory of periodic deformation of such a layer unifying the viscoelastic gravitational theory with the theory of poroelasticity without introducing additional constraints. The governing equation system and a formulation suitable for numerical calculation are given. Equations used to calculate the energy dissipation rate are also given. The analytical solutions for a homogeneous sphere are obtained using an eigenvalue approach. Simple numerical calculations assuming a homogeneous sphere reveal that a numerical instability occurs if a thick porous layer, a low permeability, or a high frequency is assumed. This instability can be avoided by choosing an appropriate interior structure model that is numerically equivalent. Different simple numerical calculations adopting a multilayered, radially varying interior profile reveal that the radial profile of the tidal heating rate for a fluid‐saturated porous layer and that for a low‐viscosity solid layer are completely different. In addition, the radial variation in porosity can lead to a factor of ∼100 increase in the local heating rate. These results indicate that future studies should consider a wider variety of detailed interior structure models. Plain Language Summary: Global periodic deformations, such as tidal and seismic motions, are fundamental phenomena that have been studied for a long time. While planetary exploration missions suggest the presence of solid‐liquid mixed layers in solar system bodies, a comprehensive theory describing deformation of such a layer has not been established. In this study, a classic geophysical approach and a classic engineering approach are unified to investigate the dynamics of such a layer. A full set of equations as well as analytical solutions are derived. A numerical issue that is likely to be encountered under typical calculation conditions is discussed. A simple calculation assuming tides on the Saturnian satellite Enceladus indicates that the radial variation in porosity can lead to a significant increase in the tidal heating rate in a shallow part of the water‐saturated rocky core. The theory established in this study will be valuable for future detailed studies. Key Points: The theory for periodic deformation of a planetary body with a global, fluid‐saturated porous layer is establishedThe procedure to make numerical calculations accurate and stable is givenThe importance of the direct calculation of the fluid flow and that of the radial porosity profile are demonstrated
- Subjects
PLANETARY exploration; FLUID flow; ENCELADUS (Satellite); NUMERICAL calculations; ANALYTICAL solutions; SHALLOW-water equations
- Publication
Journal of Geophysical Research. Planets, 2023, Vol 128, Issue 7, p1
- ISSN
2169-9097
- Publication type
Article
- DOI
10.1029/2022JE007700