Ocean worlds in the outer solar system

Nimmo, F.; Pappalardo, R.

doi:10.1002/2016je005081

Cited by 184 publications

(155 citation statements)

References 193 publications

(264 reference statements)

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“…The volume of this hydrosphere strongly varies among icy worlds, allowing the presence of different phases of ice, depending on the size of the body. All cases involve ice Ih near the surface, possibly above an ocean of liquid water (Nimmo & Pappalardo, ), while, for the largest objects, denser high‐pressure polymorphs of ice can be present beneath the ocean (e.g., Vance et al, ). If impurities behaving as antifreeze, such as ammonia or methanol, are initially present in the outer layer, the existence of a contemporary subsurface ocean is very likely (e.g., Deschamps & Sotin, ; Kamata, ; Spohn & Schubert, ).…”

Section: Ice Layer As a Tidally Heated Convective Systemmentioning

confidence: 99%

Tidally Heated Convection and the Occurrence of Melting in Icy Satellites: Application to Europa

et al. 2020

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Observations of icy satellites have revealed widespread marks of cryovolcanism. Because aqueous cryomagmas are negatively buoyant, two processes are required to explain these observations: one mechanism to generate melt close enough to the surface and another one to transport this melt to the surface. Here, we investigate the generation of melting in a systematic way, using a set of 85 numerical simulations where we vary the viscosity contrast, Rayleigh number, and tidal heating rate. Applied to Europa, considering a hydrosphere composed of pure water, our simulations suggest that isolated melt pockets can be generated close to the surface ( ∼5 km) as long as the ice layer thickness ( d*) remains modest ( 15≤d*≤35 km). However, the generation of melting becomes increasingly difficult as the amount of antifreeze compounds in the subsurface ocean increases. Furthermore, the proportion of melting increases very sharply with increasing tidal heating rate. In particular, when the tidal heating rate exceeds a threshold, an asymptotic regime is reached where the surface heat flux remains constant indicating that the tidal heat generated above this threshold is only used for melting the ice shell. In that regime, we found a direct relationship between the surface heat flux and d*. Finally, we provide a new assessment of Europa's thermal state. Based on available constraints, we propose that the ice shell thickness should exceed 15 km. However, d*∼15–35 km implies a tidal power ( >2 TW) much larger than expected. An extrapolation of the trends suggested by our results indicates that a more reasonable tidal power ( ∼1 TW) would involve d*∼50–90 km.

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Section: Ice Layer As a Tidally Heated Convective Systemmentioning

confidence: 99%

Tidally Heated Convection and the Occurrence of Melting in Icy Satellites: Application to Europa

et al. 2020

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“…En orbite autour de Saturne, Encelade est l'une de ces « lunes glacées » des planètes géantes gazeuses (voir aussi, autour de Jupiter, Ganymède et Europe), qui abriteraient un profond océan global sous une épaisse banquise permanente de plusieurs kilomètres d'épaisseur, elle aussi globale (Čadek et al, 2016 ;Nimmo et Pappalardo, 2016). La surface d'Encelade, composée de glace d'eau dont l'albédo est proche de celui de la neige fraîche, est soumise à une température moyenne de -198°C (Grundy et al, 1999 ;Verbiscer et al, 2007 ;Howett et al, 2010).…”

Section: L'albédounclassified

Climatologie comparée des planètes : un bref état des connaissances

Planchon

2017

Climatologie

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RésuméLes principaux paramètres permettant de caractériser et comparer les conditions climatiques des différentes planètes telluriques du système solaire sont développés en fonction de la distance au Soleil, de l'existence d'une atmosphère, de sa composition et ses mouvements, et enfin des paramètres orbitaux permettant d'identifier des cycles saisonniers plus ou moins accentués (obliquité et excentricité). Les conditions climatiques des planètes du système solaire font ressortir certains traits communs modulés par les caractères propres à chaque planète. Ainsi la vitesse de rotation, l'obliquité et l'excentricité introduisent, d'une part par la durée du jour et de la nuit, d'autre part par l'existence ou non de saisons, des nuances climatiques tantôt contrastées, tantôt subtiles et complexes d'une planète à une autre. La paléoclimatologie de la Terre peut aussi apporter certaines indications permettant de modéliser les conditions climatiques probables sur d'autres planètes telluriques.Mots-clés : planétologie comparée, climatologie, circulation atmosphérique, saisonnalité, paléoclimatologie. Abstract Comparative climatology of planets: A brief overview of current knowledgeThe main parameters allowing to characterize and compare the climatic features over the terrestrial planets of the Solar System are developed according to the distance from the host star; the existence of an atmosphere, its composition and motion; and the orbital parameters allowing to identify seasonal more or less contrasted oscillations (obliquity and eccentricity). The comparative climatology of the Solar System planets shows some common features subjected to many changes depending on different parameters of every planet. Like this, the rotation period (day/night duration), the obliquity and the eccentricity (seasonal oscillations) cause a wide variety of climatic conditions from a planet to an other one. Paleoclimatology of the Earth may also bring information to climate modelling of other terrestrial planets.

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“…The satellite of Saturn, Enceladus, displays a surprising amount of tectonic activity in spite of its relatively small size (Figure ) [e.g., Crow‐Willard and Pappalardo , ; Nahm and Kattenhorn , ]. Tectonic activity and geophysical and geochemical evidence indicate that a global or regional ocean is likely present underneath the ice shell [e.g., Nimmo and Pappalardo , ], with important implications for the astrobiological potential of the satellite [ Hsu et al ., ; Glein et al ., ]. The extent of that ocean, however, remains debated, with both global and regional models being proposed [e.g., Collins and Goodman , ; Thomas et al ., ].…”

Section: Introductionmentioning

confidence: 99%

The impact of a pressurized regional sea or global ocean on stresses on Enceladus

Johnston

Montési

2017

JGR Planets

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Liquid water is likely present in the interior of Enceladus, but it is still debated whether this water forms a global ocean or a regional sea and whether the present‐day situation is stable. As the heat flux of Enceladus exceeds most heat source estimates, the liquid water is likely cooling and crystallizing, which results in expansion and pressurization of the sea or ocean. We determine, using an axisymmetric Finite Element Model, the tectonic patterns that pressurization of a regional sea or global ocean might produce at the surface of Enceladus. Tension is always predicted above where the ice is thinnest and generates cracks that might be at the origin of the Tiger Stripes. Tectonic activity is also expected in an annulus around the sea if the ice shell is in contact with but slips freely along the rocky core of the satellite. Cracks at the north pole are expected if the shell slips along the core or if there is a global ocean with thin ice at the pole. Water is likely injected along the base of the ice when the shell is grounded, which may lead to cycles of tectonic activity with the shell alternating between floating and grounded states and midlatitude faulting occurring at the transition from a grounded to a floating state.

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Ocean worlds in the outer solar system

Cited by 184 publications

References 193 publications

Tidally Heated Convection and the Occurrence of Melting in Icy Satellites: Application to Europa

Tidally Heated Convection and the Occurrence of Melting in Icy Satellites: Application to Europa

Climatologie comparée des planètes : un bref état des connaissances

The impact of a pressurized regional sea or global ocean on stresses on Enceladus

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