The coupling between inertial and rotational eigenmodes in planets with liquid cores

The Earth is a rapidly rotating body. The centrifugal pull makes its shape resemble a flattened ellipsoid and Coriolis forces support waves in its fluid core, known as inertial waves. These waves can lead to global oscillations, or modes, of the fluid. Periodic variations of the Earth's rotation axis (nutations) can lead to an exchange of angular momentum between the mantle and the fluid core and excite these inertial modes. In addition to viscous torques that exist regardless of the shape of the boundaries, the small flattening of the core-mantle boundary (CMB) allows inertial modes to exert pressure torques on the mantle. These torques effectively couple the rigid-body dynamics of the Earth with the fluid dynamics of the fluid core. Here we present the first high resolution numerical model that solves simultaneously the rigid body dynamics of the mantle and the Navier-Stokes equation for the liquid core. This method takes naturally into account dissipative processes in the fluid that are ignored in current nutation models. We find that the Free Core Nutation (FCN) mode, mostly a toroidal fluid flow if the mantle has a large moment of inertia, enters into resonance with nearby modes if the mantle's moment of inertia is reduced. These mode interactions seem to be completely analogous to the ones discovered by Schmitt (2006) in a uniformly rotating ellipsoid with varying flattening.Comment: 30 pages, 19 figures. Published in the Geophysical Journal Internationa

Inertial modes of a freely rotating ellipsoidal planet and their relation to nutations

We compute the inertial modes of a freely rotating two-layer planetary model with an ellipsoidal inviscid fluid core and a perfectly rigid mantle. We present a method to derive analytical formulae for the frequencies of the Free Core Nutation (FCN) and Chandler Wobble (CW) which are valid to all orders of the dynamical flattening of the core and mantle, and we show how the FCN and CW are the direct generalisation of the purely fluid Spin-Over mode (SO) and of the Eulerian Wobble (EW) to the case where the mantle can oscillate freely around a state of steady rotation. Through a numerical computation for an axisymmetric (oblate spheroidal) planet, we demonstrate that all other inertial modes of the steadily rotating fluid core are also free modes of the freely rotating two-layer planet.Comment: 19 pages, 4 figures, accepted for publication in Planetary Science Journal (AAS

Powering the Galilean Satellites with Moon-Moon Tides

There is compelling evidence for subsurface water oceans among the three outer Galilean satellites, and evidence for an internal magma ocean in the innermost moon, Io. Tidal forces from Jupiter periodically deform these bodies, causing heating and deformation that, if measured, can probe their interior structures. In addition to Jupiter-raised tides, each moon also raises tides on the others. We investigate moon-moon tides for the first time in the Galilean moons, and show that they can cause significant heating through the excitation of high-frequency resonant tidal waves in their subsurface oceans. The heating occurs both in the crust and ocean, and can exceed that of other tidal sources and radiogenic decay if the ocean is inviscid enough. The resulting tidal deformation can be used to constrain subsurface ocean thickness. Our understanding of the thermal-orbital evolution and habitability of the Jovian system may be fundamentally altered as a result

Variants in Miro1 cause alterations of ER-mitochondria contact sites in fibroblasts from Parkinson's disease patients

Background: Although most cases of Parkinson´s disease (PD) are idiopathic with unknown cause, an increasing number of genes and genetic risk factors have been discovered that play a role in PD pathogenesis. Many of the PD‐associated proteins are involved in mitochondrial quality control, e.g., PINK1, Parkin, and LRRK2, which were recently identified as regulators of mitochondrial‐endoplasmic reticulum (ER) contact sites (MERCs) linking mitochondrial homeostasis to intracellular calcium handling. In this context, Miro1 is increasingly recognized to play a role in PD pathology. Recently, we identified the first PD patients carrying mutations in RHOT1, the gene coding for Miro1. Here, we describe two novel RHOT1 mutations identified in two PD patients and the characterization of the cellular phenotypes. Methods: Using whole exome sequencing we identified two PD patients carrying heterozygous mutations leading to the amino acid exchanges T351A and T610A in Miro1. We analyzed calcium homeostasis and MERCs in detail by live cell imaging and immunocytochemistry in patient‐derived fibroblasts. Results: We show that fibroblasts expressing mutant T351A or T610A Miro1 display impaired calcium homeostasis and a reduced amount of MERCs. All fibroblast lines from patients with pathogenic variants in Miro1, revealed alterations of the structure of MERCs. Conclusion: Our data suggest that Miro1 is important for the regulation of the structure and function of MERCs. Moreover, our study supports the role of MERCs in the pathogenesis of PD and further establishes variants in RHOT1 as rare genetic risk factors for neurodegeneration

The Science Case for Io Exploration

Io is a priority destination for solar system exploration, as it is the best natural laboratory to study the intertwined processes of tidal heating, extreme volcanism, and atmosphere-magnetosphere interactions. Io exploration is relevant to understanding terrestrial worlds (including the early Earth), ocean worlds, and exoplanets across the cosmos

Recommendations for Addressing Priority Io Science in the Next Decade

Io is a priority destination for solar system exploration. The scope and importance of science questions at Io necessitates a broad portfolio of research and analysis, telescopic observations, and planetary missions - including a dedicated New Frontiers class Io mission

Modelling the interior of Enceladus : a combined view from gravity, topography, and libration

The year 2017 saw Cassini plunge to its demise into Saturn's atmosphere, putting an end to a twenty-year odyssey that challenged our beliefs on the possible presence of water and life elsewhere in the Universe. The Cassini-Huygens mission left a rich legacy of observations of Saturn and its ever-evolving world of rings and moons. The intense geological activity discovered throughout Enceladus's south-polar terrain is a puzzle in itself: where are the geysers' water supplies? how abundant is water? has it always remained unfrozen, and if so, how? The purpose of this thesis is to address some of these questions using Cassini's measurements of Enceladus's gravity field, surface topography, and diurnal libration. The latter, a subtle modulation of the moon's spin rate over its eccentric orbit around Saturn, induces slight offsets in images taken by Cassini's cameras. To correctly interpret the observations, we develop new, mutually consistent isostasy and libration models, correct to the second order in the flattenings associated with the moon's triaxial shape. We then show that the liquid water reservoir must be a global ocean as opposed to a regional sea, and obtain the best post-Cassini constraints on the thickness of the icy crust, the ocean, and the core. To alleviate the mathematical burden, we present a systematic method to handle equations in near-spherical geometries based on series expansions in powers of the flattenings, and prove their convergence. By sharing our code TenGSHui, we hope to entice the community into more reproducible and intuitive modelling, and reconnect global geodynamics with its most fundamental principles.(SC - Sciences) -- UCL, 201

The diurnal libration and interior structure of Enceladus

We determine constraints on the ice shell and ocean of Enceladus from the observed libration at orbital period by assessing the effects of uncertainties in the size, density, rigidity, and viscosity of the internal layers and of the non-hydrostatic structure on the libration. The observed libration amplitude implies that the average thickness of the ice shell is between 14 km and 26 km and that the ocean is 21 km to 67 km thick

The diurnal libration and interior structure of Enceladus

© 2016 Elsevier Inc. We determine constraints on the ice shell and ocean of Enceladus from the observed libration at orbital period by assessing the effects of uncertainties in the size, density, rigidity, and viscosity of the internal layers and of the non-hydrostatic structure on the libration. The observed libration amplitude implies that the average thickness of the ice shell is between 14 km and 26 km and that the ocean is 21 km to 67 km thick.status: publishe