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Analytical Model of Tidal Distortion and Dissipation for a Giant Planet with a Viscoelastic Core  [PDF]
Natalia I. Storch,Dong Lai
Physics , 2015, DOI: 10.1093/mnras/stv904
Abstract: We present analytical expressions for the tidal Love numbers of a giant planet with a solid core and a fluid envelope. We model the core as a uniform, incompressible, elastic solid, and the envelope as a non-viscous fluid satisfying the $n=1$ polytropic equation of state. We discuss how the Love numbers depend on the size, density, and shear modulus of the core. We then model the core as a viscoelastic Maxwell solid and compute the tidal dissipation rate in the planet as characterized by the imaginary part of the Love number $k_2$. Our results improve upon existing calculations based on planetary models with a solid core and a uniform ($n=0$) envelope. Our analytical expressions for the Love numbers can be applied to study tidal distortion and viscoelastic dissipation of giant planets with solid cores of various rheological properties, and our general method can be extended to study tidal distortion/dissipation of super-earths.
Understanding tidal dissipation in gaseous giant planets from their core to their surface  [PDF]
M. Guenel,S. Mathis,F. Remus
Physics , 2014, DOI: 10.1051/epjconf/201510106029
Abstract: Tidal dissipation in planetary interiors is one of the key physical mechanisms that drive the evolution of star-planet and planet-moon systems. Tidal dissipation in planets is intrinsically related to their internal structure. In particular, fluid and solid layers behave differently under tidal forcing. Therefore, their respective dissipation reservoirs have to be compared. In this work, we compute separately the contributions of the potential dense rocky/icy core and of the convective fluid envelope of gaseous giant planets, as a function of core size and mass. We demonstrate that in general both mechanisms must be taken into account.
Melting the core of giant planets: impact on tidal dissipation  [PDF]
S. Mathis
Physics , 2015,
Abstract: Giant planets are believed to host central dense rocky/icy cores that are key actors in the core-accretion scenario for their formation. In the same time, some of their components are unstable in the temperature and pressure regimes of central regions of giant planets and only ab-initio EOS computations can address the question of the state of matter. In this framework, several works demonstrated that erosion and redistribution of core materials in the envelope must be taken into account. These complex mechanisms thus may deeply modify giant planet interiors for which signatures of strong tidal dissipation have been obtained for Jupiter and Saturn. The best candidates to explain this dissipation are the viscoelastic dissipation in the central dense core and turbulent friction acting on tidal inertial waves in their fluid convective envelope. In this work, we study the consequences of the possible melting of central regions for the efficiency of each of these mechanisms.
Understanding tidal dissipation in gaseous giant planets : the respective contributions of their core and envelope  [PDF]
M. Guenel,S. Mathis,F. Remus
Physics , 2014,
Abstract: Tidal dissipation in planetary interiors is one of the key physical mechanisms that drive the evolution of star-planet and planet-moon systems. New constraints are now obtained both in the Solar and exoplanetary systems. Tidal dissipation in planets is intrinsically related to their internal structure. In particular, fluid and solid layers behave differently under tidal forcing. Therefore, their respective dissipation reservoirs have to be compared. In this work, we compute separately the contributions of the potential dense rocky/icy core and of the convective fluid envelope of gaseous giant planets, as a function of core size and mass. We then compare the associated dissipation reservoirs, by evaluating the frequency-average of the imaginary part of the Love numbers $k^2_2$ in each region. We demonstrate that in general both mechanisms must be taken into account.
Scaling laws to quantify tidal dissipation in star-planet systems  [PDF]
Pierre Auclair-Desrotour,Stéphane Mathis,Christophe Le Poncin-Lafitte
Physics , 2015,
Abstract: Planetary systems evolve over secular time scales. One of the key mechanisms that drive this evolution is tidal dissipation. Submitted to tides, stellar and planetary fluid layers do not behave like rocky ones. Indeed, they are the place of resonant gravito-inertial waves. Therefore, tidal dissipation in fluid bodies strongly depends on the excitation frequency while this dependence is smooth in solid ones. Thus, the impact of the internal structure of celestial bodies must be taken into account when studying tidal dynamics. The purpose of this work is to present a local model of tidal gravito-inertial waves allowing us to quantify analytically the internal dissipation due to viscous friction and thermal diffusion, and to study the properties of the resonant frequency spectrum of the dissipated energy. We derive from this model scaling laws characterizing tidal dissipation as a function of fluid parameters (rotation, stratification, diffusivities) and discuss them in the context of star-planet systems.
Are the Kepler Near-Resonance Planet Pairs due to Tidal Dissipation?  [PDF]
Man Hoi Lee,D. Fabrycky,D. N. C. Lin
Physics , 2013, DOI: 10.1088/0004-637X/774/1/52
Abstract: The multiple-planet systems discovered by the Kepler mission show an excess of planet pairs with period ratios just wide of exact commensurability for first-order resonances like 2:1 and 3:2. In principle, these planet pairs could have both resonance angles associated with the resonance librating if the orbital eccentricities are sufficiently small, because the width of first-order resonances diverges in the limit of vanishingly small eccentricity. We consider a widely-held scenario in which pairs of planets were captured into first-order resonances by migration due to planet-disk interactions, and subsequently became detached from the resonances, due to tidal dissipation in the planets. In the context of this scenario, we find a constraint on the ratio of the planet's tidal dissipation function and Love number that implies that some of the Kepler planets are likely solid. However, tides are not strong enough to move many of the planet pairs to the observed separations, suggesting that additional dissipative processes are at play.
Unravelling tidal dissipation in gaseous giant planets  [PDF]
Mathieu Guenel,Stéphane Mathis,Fran?oise Remus
Physics , 2014, DOI: 10.1051/0004-6361/201424010
Abstract: Tidal dissipation in planetary interiors is one of the key physical mechanisms that drive the evolution of star-planet and planet-moon systems. New constraints are now obtained both in the Solar and exoplanetary systems. Tidal dissipation in planets is intrinsically related to their internal structure. In particular, fluid and solid layers behave differently under tidal forcing. Therefore, their respective dissipation reservoirs have to be compared. In this letter, we compute separately the contributions of the potential dense rocky/icy core and the convective fluid envelope of gaseous giant planets, as a function of core size and mass. We then compare the associated dissipation reservoirs, by evaluating the frequency-average of the imaginary part of the Love numbers $k^2_2$ in each region. In the case of Jupiter and Saturn-like planets, we show that the viscoelastic dissipation in the core could dominate the turbulent friction acting on tidal inertial waves in the envelope. However, the fluid dissipation would not be negligible. This demonstrates that it is necessary to build complete models of tidal dissipation in planetary interiors from their deep interior to their surface without any arbitrary a-priori.
Anelastic tidal dissipation in multi-layer planets  [PDF]
F. Remus,S. Mathis,J. -P. Zahn,V. Lainey
Physics , 2012, DOI: 10.1051/0004-6361/201118595
Abstract: Earth-like planets have viscoelastic mantles, whereas giant planets may have viscoelastic cores. The tidal dissipation of such solid regions, gravitationally perturbed by a companion body, highly depends on their rheology and on the tidal frequency. Therefore, modelling tidal interactions presents a high interest to provide constraints on planets' properties and to understand their history and their evolution, in our Solar System or in exoplanetary systems. We examine the equilibrium tide in the anelastic parts of a planet whatever the rheology, taking into account the presence of a fluid envelope of constant density. We show how to obtain the different Love numbers that describe its tidal deformation. Thus, we discuss how the tidal dissipation in solid parts depends on the planet's internal structure and rheology. Finally, we show how the results may be implemented to describe the dynamical evolution of planetary systems. The first manifestation of the tide is to distort the shape of the planet adiabatically along the line of centers. Then, the response potential of the body to the tidal potential defines the complex Love numbers whose real part corresponds to the purely adiabatic elastic deformation, while its imaginary part accounts for dissipation. This dissipation is responsible for the imaginary part of the disturbing function, which is implemented in the dynamical evolution equations, from which we derive the characteristic evolution times. The rate at which the system evolves depends on the physical properties of tidal dissipation, and specifically on how the shear modulus varies with tidal frequency, on the radius and also the rheological properties of the solid core. The quantification of the tidal dissipation in solid cores of giant planets reveals a possible high dissipation which may compete with dissipation in fluid layers.
Tidal dissipation in multi-planet systems and constraints to orbit-fitting  [PDF]
Jacques Laskar,Gwena?l Boué,Alexandre C. M. Correia
Physics , 2011, DOI: 10.1051/0004-6361/201116643
Abstract: We present here in full details the linear secular theory with tidal damping that was used to constraint the fit of the HD10180 planetary system in (Lovis et al. 2011). The theory is very general and can provide some intuitive understanding of the final state of a planetary system when one or more planets are close to their central star. We globally recover the results of (Mardling 2007), but we show that in the HD209458 planetary system, the consideration of the tides raised by the central star on the planet lead to believe that the eccentricity of HD209458b is most probably much smaller than 0.01.
Tidal Dissipation in Planet-Hosting Stars: Damping of Spin-Orbit Misalignment and Survival of Hot Jupiters  [PDF]
Dong Lai
Physics , 2011, DOI: 10.1111/j.1365-2966.2012.20893.x
Abstract: Observations of hot Jupiters around solar-type stars with very short orbital periods (~day) suggest that tidal dissipation in such stars is not too efficient so that these planets can survive against rapid orbital decay. This is consistent with recent theoretical works, which indicate that the tidal Q of planet-hosting stars can indeed be much larger than the values inferred from stellar binaries. On the other hand, recent measurements of Rossiter-McLaughlin effects in transiting hot Jupiter systems not only reveal that many such systems have misaligned stellar spin with respect to the orbital axis, but also show that systems with cooler host stars tend to have aligned spin and orbital axes. Winn et al. suggested that this obliquity - temperature correlation may be explained by efficient damping of stellar obliquity due to tidal dissipation in the star. This explanation, however, is in apparent contradiction with the survival of these short-period hot Jupiters. We show that in the solar-type parent stars of close-in exoplanetary systems, the effective tidal Q governing the damping of stellar obliquity can be much smaller than that governing orbital decay. This is because for misaligned systems, the tidal potential contains a Fourier component with frequency equal to the stellar spin frequency (in the rotating frame of the star). This component can excite inertial waves in the convective envelope of the star, and the dissipation of inertial waves then leads to a spin-orbit alignment torque, but not orbital decay. By contrast, for aligned systems, such inertial wave excitation is forbidden since the tidal forcing frequency is much larger than the stellar spin frequency. We derive a general effective tidal evolution theory for misaligned binaries, taking account of different tidal responses and dissipation rates for different tidal forcing components.
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