Crustal failure on icy Moons from a strong tidal encounter

Crustal failure on icy Moons from a strong tidal encounter

Authors:

Quillen et al

Abstract:

Close tidal encounters among large planetesimals and Moons should have been more common than grazing or normal impacts. Using a mass spring model within an N-body simulation, we simulate the deformation of the surface of an elastic spherical body caused by a close parabolic tidal encounter with a body that has similar mass as that of the primary body. Such an encounter can induce sufficient stress on the surface to cause brittle failure of an icy crust and simulated fractures can extend a large fraction of the radius of body. Strong tidal encounters may be responsible for the formation of long graben complexes and chasmata in ancient terrain of icy Moons such as Dione, Tethys, Ariel and Charon.

The Tides of Snowball Earth Would Have Been Greater

Tides of global ice-covered oceans

Author:

Wunsch

Abstract:

The tides of an ice-covered ocean are examined using a Cartesian representation of the elastic and fluid equations. Although unconstrained by any observations, the ocean tides of a Neoproterozoic “snowball” Earth could have been significantly larger than they are today. Time-mean tidal-residual circulations would then have been set up that are competitive with the circulation driven by geothermal heating. In any realistic configuration, the snowball Earth would have had an ice cover that is in the thin shell limit, but by permitting the ice thickness to become large, more interesting ice tidal response can be found, ones conceivably of application to bodies in the outer Solar System or hypothetical exoplanets. Little can be said concerning a reduction in tidal dissipation necessary to avoid a crisis in the history of the lunar orbit.

Crustal Failure on Icy Moons and Satellites from a Strong Tidal Encounter

Crustal Failure on Icy Moons and Satellites from a Strong Tidal Encounter

Authors:

Quillen et al

Abstract:

Close tidal encounters among large planetesimals and satellites should have been more common than grazing or normal impacts. Using a mass spring model within an N-body simulation, we simulate the deformation of the surface of an elastic spherical body caused by a close parabolic tidal encounter with a body that has similar mass as that of the primary body. Such an encounter can induce sufficient stress on the surface to cause brittle failure of an icy crust and simulated fractures can extend a large fraction of the radius of body. Strong tidal encounters may be responsible for the formation of long graben complexes and chasmata in ancient terrain of icy moons and satellites such as Dione, Tethys, Ariel and Charon.

Modeling the Early Earth-Moon Tidal Interaction

Early evolution of the Earth–Moon system with a fast-spinning Earth

Authors:

Wisdom et al

Abstract:

The isotopic similarity of the Earth and Moon has motivated a recent investigation of the formation of the Moon with a fast-spinning Earth (Cuk, M., Stewart, S.T., [2012]. Science, doi:10.1126/science.1225542). Angular momentum was found to be drained from the system through a resonance between the Moon and Sun. They found a narrow range of parameters that gave results consistent with the current angular momentum of the Earth–Moon system. However, a tidal model was used that was described as approximating a constant Q tidal model, but it was not a constant Q model. Here we use a conventional constant Q tidal model to explore the process. We find that there is still a narrow range of parameters in which angular momentum is withdrawn from the system that corresponds roughly to the range found earlier, but the final angular momentum is too low to be consistent with the Earth–Moon system. Exploring a broader range of parameters we find a new phenomenon, not found in the earlier work, that extracts angular momentum from the Earth–Moon system over a broader range of parameters. The final angular momentum is more consistent with the actual angular momentum of the Earth–Moon system. We develop a simple model that exhibits the phenomenon.

Improved Methods to Detect Europa's Tides Through Flybys

Improved Detection of Tides at Europa with radiometric and optical tracking during flybys

Authors:

Park et al

Abstract:

Due to its eccentric orbit about Jupiter, Europa experiences periodic tidal deformation, which causes changes in its gravitational field and induces both radial and transverse displacements of the surface. The amplitude and phase of these tidal changes are diagnostic of internal structure, and can be measured with sufficient radiometric and optical tracking of a spacecraft during a series of flyby encounters with Europa. This paper presents results of the simulated accuracy for recovery of the tides of Europa through measuring the second-degree tidal Love numbers k2k2, h2h2, and l2l2. A reference trajectory, which consists of a total of 45 close flybys, was considered and a detailed covariance analysis was performed. The study was based on Earth-based Doppler tracking during ±2±2 hours of each periapsis passage and surface imaging data taken below 500 km altitude. The result shows that the formal uncertainty of the second-degree tidal Love numbers can be estimated to σk2=0.01σk2=0.01, σh2=0.02σh2=0.02, and σl2=0.01σl2=0.01, which is sufficient to constrain the global ice thickness to about 10 km under reasonable assumptions. Moreover, the forced librations of Europa can be measured to 0.3"" accuracy, which can further constrain Europa's interior structure.

Explaining the Plume Differences Between Europa and Enceladus

Linking Europa's plume activity to tides, tectonics, and liquid water

Authors:

Rhoden et al

Abstract:

Much of the geologic activity preserved on Europa's icy surface has been attributed to tidal deformation, mainly due to Europa's eccentric orbit. Although the surface is geologically young (30 - 80 Myr), there is little information as to whether tidally-driven surface processes are ongoing. However, a recent detection of water vapor near Europa's south pole suggests that it may be geologically active. Initial observations indicated that Europa's plume eruptions are time-variable and may be linked to its tidal cycle. Saturn's moon, Enceladus, which shares many similar traits with Europa, displays tidally-modulated plume eruptions, which bolstered this interpretation. However, additional observations of Europa at the same time in its orbit failed to yield a plume detection, casting doubt on the tidal control hypothesis. The purpose of this study is to analyze the timing of plume eruptions within the context of Europa's tidal cycle to determine whether such a link exists and examine the inferred similarities and differences between plume activity on Europa and Enceladus.

Tides on Europa

Tides on Europa: The membrane paradigm

Author:

Beuthe

Abstract:

Jupiter’s moon Europa has a thin icy crust which is decoupled from the mantle by a subsurface ocean. The crust thus responds to tidal forcing as a deformed membrane, cold at the top and near melting point at the bottom. In this paper I develop the membrane theory of viscoelastic shells with depth-dependent rheology with the dual goal of predicting tidal tectonics and computing tidal dissipation. Two parameters characterize the tidal response of the membrane: the effective Poisson’s ratio View the MathML sourceν¯ and the membrane spring constant Λ , the latter being proportional to the crust thickness and effective shear modulus. I solve membrane theory in terms of tidal Love numbers, for which I derive analytical formulas depending on View the MathML sourceΛ,ν¯, the ocean-to-bulk density ratio and the number View the MathML sourcek2∘ representing the influence of the deep interior. Membrane formulas predict h2h2 and k2k2 with an accuracy of a few tenths of percent if the crust thickness is less than one hundred kilometers, whereas the error on l2l2 is a few percents. Benchmarking with the thick-shell software SatStress leads to the discovery of an error in the original, uncorrected version of the code that changes stress components by up to 40%. Regarding tectonics, I show that different stress-free states account for the conflicting predictions of thin and thick shell models about the magnitude of tensile stresses due to nonsynchronous rotation. Regarding dissipation, I prove that tidal heating in the crust is proportional to Im(Λ)Im(Λ) and that it is equal to the global heat flow (proportional to Im(k2)Im(k2)) minus the core-mantle heat flow (proportional to View the MathML sourceIm(k2∘)). As an illustration, I compute the equilibrium thickness of a convecting crust. More generally, membrane formulas are useful in any application involving tidal Love numbers such as crust thickness estimates, despinning tectonics or true polar wander.

Oceanic Tidal Heating in the Icy Moons is Significant

Comparative estimates of the heat generated by ocean tides on icy satellites in the outer Solar System

Author:

Tyler

Abstract:

This study illuminates scenarios whereby the heat produced by the dissipation of ocean tides is significant in the heat budgets maintaining liquid oceans on icy satellites in the outer Solar System. It has been shown in previous work that ocean tides, if resonantly forced, can supply heat at or exceeding the rates necessary for maintaining these oceans. It has also been shown that because of feedbacks these resonant configurations may be unavoidable under typical situations. This study extends from the previous work and seeks to examine the full set of dynamically-consistent ocean tidal solutions to describe the parameter dependencies that may cause one ocean to become trapped in such a vigorous ocean state while allowing another to freeze—why do some of these satellites have oceans, and others do not? It is found that even with no other sources of heat, a liquid ocean on many of these satellites would be maintained by ocean tidal heat because the process of freezing (which changes the thickness of the remaining liquid ocean and thereby the eigenmodes) would push the ocean into a resonant configuration, with the associated increase in heat production preventing further freezing and stabilizing the configuration. An ocean on Io or Mimas would suffer extreme tides (with heat generated exceeding 1 W/m2) unless an implausibly large volume of water were present to lift the eigenmodes of the configuration out of resonance with the tidal forces. Europa can maintain a thick (∼∼100 km) ocean due to an obliquity-forced tidal resonance, while parameters for most other satellites suggest eccentricity-driven resonance scenarios involving much thinner ocean thicknesses (1-10’s km). But these thin ocean thickness in the latter scenarios will be altered by ice cover: As the ice cover damps the ocean tidal response, significant heat is still generated which would stall freezing but the ocean thicknesses are modified to larger values than would be expected without ice cover.

How Grooved Terrain on Icy Moons Formed

A Common Origin for Ridge-and-Trough Terrain on Icy Satellites by Sluggish Lid Convection

Authors:

Barr et al

Abstract:

Ridge and trough terrain is a common landform on icy satellites of the outer solar system. Examples include the grooved terrain on Ganymede, gray bands on Europa, coronae on Uranus's moon Miranda, and ridges and troughs in the northern plains of Saturn's small, but active, moon Enceladus. Regardless of setting, the heat flow and strain rates associated with the formation of each of these terrains are similar: heat flows of order tens to a hundred milliwatts per meter squared, and deformation rates of order 10−16 to 10−12 s−1. Barr (2008) and Hammond & Barr (2014a) have previously shown that the conditions associated with the formation of ridge and trough terrain on Ganymede and the south polar terrain on Enceladus are consistent with solid-state ice shell convection in a shell with a weak surface. Here, we show that sluggish lid convection can simultaneously create the heat flow and deformation appropriate for the formation of ridge and trough terrains on a number of satellites. This conclusion holds regardless of the thickness of the satellites' ice shells. For convection to deform their surfaces, the ice shells must have yield stresses similar in magnitude to the daily tidal stresses exerted by the gravitational pull from their parent planets. This suggests that tidal and convective stresses must act together to deform the surface, and that the spatial pattern of tidal cracking on the surfaces of the moons controls the locations of ridge and trough terrain.

Mars may be Causing Asteroid Quakes

or nearly as long as astronomers have been able to observe asteroids, a question has gone unanswered: Why do the surfaces of most asteroids appear redder than meteorites — the remnants of asteroids that have crashed to Earth?

In 2010, Richard Binzel, a professor of planetary sciences at MIT, identified a likely explanation: Asteroids orbiting in our solar system's main asteroid belt, situated between Mars and Jupiter, are exposed to cosmic radiation, changing the chemical nature of their surfaces and reddening them over time. By contrast, Binzel found that asteroids that venture out of the main belt and pass close to Earth feel the effects of Earth's gravity, causing "asteroid quakes" that shift surface grains, exposing fresh grains underneath. When these "refreshed" asteroids get too close to Earth, they break apart and fall to its surface as meteorites.

Since then, scientists have thought that close encounters with Earth play a key role in refreshing asteroids. But now Binzel and colleague Francesca DeMeo have found that Mars can also stir up asteroid surfaces, if in close enough contact. The team calculated the orbits of 60 refreshed asteroids, and found that 10 percent of these never cross Earth's orbit. Instead, these asteroids only come close to Mars, suggesting that the Red Planet can refresh the surfaces of these asteroids.

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Tidal Effects of Non Gas Giants on Warm Jupiter Exoplanet Evolution

SMALL INNER COMPANIONS OF WARM JUPITERS: LIFETIMES AND LEGACIES

Authors:

Christa Van Laerhoven and Richard Greenberg

Abstract:

Although warm Jupiters are generally too far from their stars for tides to be important, the presence of an inner planetary companion to a warm Jupiter can result in tidal evolution of the system. Insight into the process and its effects comes form classical secular theory of planetary perturbations. The lifetime of the inner planet may be shorter than the age of the system, because the warm Jupiter maintains its eccentricity and hence promotes tidal migration into the star. Thus a warm Jupiter observed to be alone in its system might have previously cleared away any interior planets. Before its demise, even if an inner planet is of terrestrial scale, it may promote damping of the warm Jupiter's eccentricity. Thus any inferences of the initial orbit of an observed warm Jupiter must include the possibility of a greater initial eccentricity than would be estimated by assuming it had always been alone. Tidal evolution involving multiple planets also enhances the internal heating of the planets, which readily exceeds that of stellar radiation for the inner planet, and may be great enough to affect the internal structure of warm Jupiters. Secular theory gives insight into the tidal processes, providing, among other things, a way to constrain eccentricities of transiting planets based on estimates of the tidal parameter Q.