Galilean Satellites Of Jupiter Research Articles

Hydrodynamic modelling of dynamical tide dissipation in Jupiter’s interior as revealed by Juno

Context. The Juno spacecraft has acquired exceptionally precise data on Jupiter’s gravity field, offering invaluable insights into Jupiter’s tidal response, interior structure, and dynamics, establishing crucial constraints. Aims. We aim to develop a new model for calculating Jupiter’s tidal response based on its latest interior model, while also examining the significance of different dissipation processes for the evolution of its system. We studied the dissipation of dynamical tides in Jupiter by thermal, viscous, and molecular diffusivities acting on gravito-inertial waves in stably stratified zones and inertial waves in convection ones. Methods. We solved the linearised equations for the equilibrium tide. Next, we computed the dynamical tides using linear hydrodynamical simulations based on a spectral method. The Coriolis force is fully taken into account, but the centrifugal effect is neglected. We studied the dynamical tides occurring in Jupiter using internal structure models that respect Juno’s constraints. We specifically looked at the dominant quadrupolar tidal components, and our focus is on the frequency range that corresponds to the tidal frequencies associated with Jupiter’s Galilean satellites. Results. By incorporating the different dissipation mechanisms, we calculated the total dissipation and determined the imaginary part of the tidal Love number. We find a significant frequency dependence in dissipation spectra, indicating a strong relationship between dissipation and forcing frequency. Furthermore, our analysis reveals that, in the chosen parameter regime in which kinematic viscosity and thermal and molecular diffusivities are equal, the dominant mechanism contributing to dissipation is viscosity, exceeding both thermal and chemical dissipation in magnitude. We find that the presence of stably stratified zones plays an important role in explaining the high dissipation observed in Jupiter.

Tectonic analysis of a newly identified putative cryovolcanic field on Europa

More and more attention is devoted to the icy moons of the Solar System, including Europa, the second Galilean satellite of Jupiter, since the discovery of potential liquid water and the possibility of extra-terrestriallife harbored in its subsurface ocean below its icy crust. Along with the renaissanceof the study of icy satellites, the ongoing missions, such as Europa Clipper and JUICE (JUpiter ICy moons Explorer), are also part of such rejuvenation of icy satellite research.One of the leading research topics connected to Europa is understanding its surface renewal, including the interaction between the subsurface ocean and the icy crust. One of the longest-lasting and still unsettled debates related to Europa is about the nature of the potentially active cryovolcanism, which may play an essential role in the interaction between the surface of the Jovian moon and the underlying subsurface ocean. Our study focuses on the geological-geomorphological characterization of a newly identified putative cryovolcanic field found on the surface of Europa. Various volcanic structures, possibly in multiple stages of maturity, were identified. The executed geological analysis in the surroundings of the volcanoes suggests strong local influence during the formation of cryovolcanic cones working together with the overall global-scale stress fields appearing in the ice crust of Europa.

Laplace-like resonances with tidal effects

The first three Galilean satellites of Jupiter, Io, Europa, and Ganymede, move in a dynamical configuration known as the Laplace resonance, which is characterized by a 2:1 ratio of the rates of variation in the mean longitudes of Io-Europa and a 2:1 ratio of Europa-Ganymede. We refer to this configuration as a 2:1&2:1 resonance. We generalize the Laplace resonance among three satellites, S1, S2, and S3, by considering different ratios of the mean-longitude variations. These resonances, which we call Laplace-like, are classified as first order in the cases of the 2:1&2:1, 3:2&3:2, and 2:1&3:2 resonances, second order in the case of the 3:1&3:1 resonance, and mixed order in the case of the 2:1&3:1 resonance. We consider a model that includes the gravitational interaction with the central body together with the effect due to its oblateness, the mutual gravitational influence of the satellites S1, S2, and S3 and the secular gravitational effect of a fourth satellite S4, which plays the role of Callisto in the Galilean system. In addition, we consider the dissipative effect due to the tidal torque between the inner satellite and the central body. We investigate these Laplace-like resonances by studying different aspects: (i) we study the survival of the resonances when the dissipation is included, taking two different expressions for the dissipative effect in the case of a fast- or a slowly rotating central body, (ii) we investigate the behavior of the Laplace-like resonances when some parameters are varied, specifically, the oblateness coefficient, the semimajor axes, and the eccentricities of the satellites, (iii) we analyze the linear stability of first-order resonances for different values of the parameters, and (iv) we also include the full gravitational interaction with S4 to analyze its possible capture into resonance. The results show a marked difference between first-, second-, and mixed-order resonances, which might find applications when the evolutionary history of the satellites in the Solar System are studied, and also in possible actual configurations of extrasolar planetary systems.

A 2020 Observational Perspective of Io

Jupiter's Galilean satellite Io is one of the most remarkable objects in our Solar System. The tidal heating Io undergoes through its orbital resonance with Europa and Ganymede has resulted in a body rich in active silicate volcanism. Over the past decades, Io has been observed from ground-based and Earth-orbiting telescopes and by several spacecraft. In this review we summarize the progress made toward our understanding of the physical and chemical processes related to Io and its environment since the Galileo era. Io science has been revolutionized by the use of adaptive optics techniques on large, 8- to 10-m telescopes. The resultant ever-increasing database, mapping the size, style, and spatial distribution of Io's diverse volcanoes, has improved our understanding of Io's interior structure, its likely composition, and the tidal heating process. Additionally, new observations of Io's atmosphere obtained with these large optical/infrared telescopes and the Atacama Large Millimeter/submillimeter Array reveal the presence of volcanic plumes, the (at times) near-collapse of Io's atmosphere during eclipse, and the interactions of plumes with the sublimation atmosphere. ▪ Extensive new data sets of Io at ultraviolet, mid- to near-infrared, and radio wavelengths have been gathered since the Galileo era. ▪ New data and models inform us about tidal heating, surface properties, and magma composition across Io—although key questions remain. ▪ Atmospheric observations indicate a dominant sublimation-supported component and reinforce the presence of stealth volcanism. ▪ Observations of volcanic plumes show high gas velocities (up to ∼1 km/s) and their effect on Io's atmosphere.

Remote sensing of planetary space environment

Planetary space, a critical region of mass and energy exchange between the planet and the interplanetary space, is an integral part of the planetary multi-layer coupling system. Atmospheres of different compositions and plasmas of different densities and energies exist in planetary space, where mass transportation at different temporal and spatial scales and various energy deposition and dissipation processes occur. These processes are driven by the changes in the solar wind and the internal driving forces of the planet. Knowledge pertaining to the global mass and energy transportation in planetary space is essential to investigate the mass escape from the planets. Understanding the forces and physical processes that drive changes in the planetary space environment is not only beneficial to protecting the life, technical systems, and infrastructures on the Earth, but is also helpful in understanding the past and future. In this regards, the systematic and overall view of planetary space environments is necessary for planetary science. Optical remote sensing implies a measurement made by indirect or “remote” means, which relies upon either emitted, reflected, or scattered optical radiation. There are three main types of optical remote sensing technologies, namely imaging (photography), spectrograph, and spectrographic imaging. Scientific application of optical remote sensing dates back to 1906 when G. Galilei constructed the first astronomical telescope, using which he discovered the four Galilean satellites of Jupiter and the phase variation of Venus. Since then, several discoveries in planetary science have been made by means of optical remote sensing, such as the discovery of new planets and their moons, the discovery of the primary compositions of planetary atmospheres, global convection of cold plasma in Earth’s space, the discovery of planetary aurora (Earth, Mars, Jupiter, Saturn) and volcanic activity on Io, and water eruption on Enceladus. The optical remote sensing method overcomes the difficulties of capturing global views and distinguishing spatial and temporal variations in in-situ particle and field detections. Furthermore, through an overview of the history of planetary optical remote sensing, we propose a development strategy for planetary optical remote sensing, in China, based on the national deep-space exploration plan. A “Quaternity” planetary optical detection system that integrates ground-based, balloon-borne, space-based, and moon-based optical remote sensing is proposed. For example, the Institute of Geology and Geophysics, Chinese Academy of Sciences (IGGCAS) is planning to construct a ground-based optical telescope with an aperture of ~1.5 m in Northwest China to monitor the volcanic activity on Io and to conduct other planetary observations. As the first planetary optical remote sensing project in China, the balloon-borne planetary optical remote sensing for the Scientific Experiment System in Near Space (SENSE) Program is introduced in detail. The SENSE Program is a five-year Strategic Priority Research Program of the Chinese Academy of Sciences, which began in 2018. A balloon-borne Planetary Atmospheric Spectroscopic Telescope (PAST) with an aperture of 0.8 m will be launched into the stratosphere at the height of 35–40 km to image the planetary atmosphere and plasma in the ultraviolet and visible range. The main scientific target of PAST is to comparatively study the diversity of the planetary space environment and their different drivers. Test and scientific flights are scheduled in 2021 and 2022 in Northwest China and potentially in polar regions. By using the data from PAST and in combination with other data (such as Jupiter’s auroral images from the Hubble Space Telescope, Mars’ space environment data from Mars Atmosphere and Volatile Evolution mission, and Jupiter’s space environment data from Juno mission), the couplings between planetary atmosphere and plasma will be investigated to characterize the diversity of the evolution of the planetary space environment.

Can Earth-like plate tectonics occur in ocean world ice shells?

The outer H2O ice shell of Europa, a Galilean satellite of Jupiter thought to exhibit a global interior water ocean, shows evidence for plate-like surface motions along tectonic boundaries. In this study, we investigate whether forces similar to those that drive plate tectonics on Earth may drive plate motions on icy satellites. We focus on whether the forces of slab pull and ridge push, driven by thermal and compositional buoyancy, can overcome the mechanical forces resisting plate motions to sustain interaction between surface ice and the interior ocean. We find that Earth-like plate tectonics is implausible within the outer ice shell of icy satellites because the forces resisting self-sustaining plate cycling are of significantly greater order than the driving forces. In the case of Ganymede and Triton, if it has a thick shell, plate tectonics would require warm, low-viscosity slabs to remain intact for timescales that are orders of magnitude longer than those of interior convection.

The PHEMU15 catalogue and astrometric results of the Jupiter's Galilean satellite mutual occultation and eclipse observations made in 2014–2015

During the 2014-2015 mutual events season, the Institut de Mecanique Celeste et de Calcul desEphemerides (IMCCE), Paris, France, and the Sternberg Astronomical Institute (SAI), Moscow, Russia, led an international observation campaign to record ground-based photomet-ric observations of Galilean moon mutual occultations and eclipses. We focused on processing the complete photometric observations data base to compute new accurate astrometric positions. We used our method to derive astrometric positions from the light curves of the events.

Observations of the Galilean satellites of Jupiter with Pulkovo Normal Astrograph during 2009–2011

The paper presents the results of observations of Jupiter and its Galilean moons, performed with the Normal Astrograph (D/F=0.33 m/3.5 m, CCD S2C, FOV 18′ × 16′) at Pulkovo observatory during 2009–2011. We obtained 140 positions of the Galilean satellites and 42 calculated positions of Jupiter in the system of UCAC4 (ICRS, J2000.0) catalogue. The equatorial coordinates of satellites have been compared to eight most current theories of planetary and satellite motion. The average residuals between the observed and calculated coordinates (O–C) using the selected theories of motion do not exceed 0.08″. The behavior and magnitudes of the (O–C) residuals in the positions of Ganymede and Callisto satellites show that the theory of their motion was elaborated worse than in the case of Io and Europa satellites. Distribution of the (O-C) residuals for Callisto differs from a normal distribution. Comparison of the calculated equatorial coordinates of Jupiter, based on the observed positions of satellites and their theoretical Jovi-centric coordinates calculated using the INPOP10 theory of planetary motion revealed satisfactory results. The average residuals are, respectively, (O–C)α = 0.040″ and (O–C)δ =–0.053″ assuming the normal distribution law.

Searching for capture and escape trajectories around Jupiter using its Galilean satellites

This paper has the goal of searching for natural trajectories that can be used for a particle or a spacecraft coming from a region of the space far from Jupiter system to be captured into this system by making close approaches with the Galilean satellites of the planet. The opposite situation is also possible and escape trajectories can also be found. This type of maneuver is called “Swing-By” and it is usual in astrodynamics. It was used in many space missions to reduce the fuel consumption by gaining or loosing energy from the gravity of a celestial body. Several famous examples are the Voyager, Cassini, Galileo and other missions. The idea of the present research is to study this type of maneuver using the Galilean satellites of Jupiter, to search for trajectories that change the two-body energy (particle or spacecraft)–(Jupiter) from positive to negative (a capture trajectory) or from negative to positive (an escape trajectory). Those trajectories can be used for a spacecraft going or leaving the planet Jupiter or to explain how particles can be captured or escape from Jupiter system by close approaches with the Galilean satellites. Initial conditions are varied to cover the whole possible alternatives and then small regions of captures and escapes are identified. After that, a study is made to see the accuracy of the Tisserand’s method when applied to those close approach trajectories.

Characteristic features in the spectra of Europa, Ganymede, and Callisto

The results of ground-based spectrophotometry of the icy Galilean satellites of Jupiter—Europa, Ganymede, and Callisto—are discussed. The observations were carried out in the 0.39–0.92 μm range with the use of the CCD spectrometer mounted on the 1.25-m telescope of the Crimean laboratory of the Sternberg Astronomical Institute in March 2004. It is noted that the calculated reflectance spectra of the satellites mainly agree with the analogous data of the earlier ground-based observations and investigations in the Voyager and Galileo space missions. The present study was aimed at identifying new weak absorption bands (with the relative intensity of ∼3–5%) in the reflectance spectra of these bodies with laboratory measurements (Landau et al., 1962; Ramaprasad et al., 1978; Burns, 1993; Busarev et al., 2008). It has been ascertained that the spectra of all of the considered objects contain weak absorption bands of molecular oxygen adsorbed into water ice, which is apparently caused by the radiative implantation of O+ ions into the surface material of the satellites in the magnetosphere of Jupiter. At the same time, spectral features of iron of different valence (Fe2+ and Fe3+) values typical of hydrated silicates were detected on Ganymede and Callisto, while probable indications of methane of presumably endogenous origin, adsorbed into water ice, were found on Europa. The reflectance spectra of the icy Galilean satellites were compared to the reflectance spectra of the asteroids 51 Nemausa (C-class) and 92 Undina (X-class).

A Study of Swing-By Trajectories in the Galilean Satellites of Jupiter

The Swing-By maneuver is a technique that has been under use in space missions for many years now, with the goal of reducing the fuel consumption of a spacecraft travelling near a massive body and that requires a modification in its orbit. Several well-known missions used this approach, like Voyager, Galileo, Cassini, Ulysses, and many others. The present research has the goal of studying and classifying Swing-by maneuvers around the Galilean satellites of Jupiter. The approach to solve this problem is to simulate a large variety of initial conditions and then to perform a classification of the orbits according to the effects that the close approach made in the orbit of the spacecraft, in particular looking for captures and escapes that resulted from the close approach.

The accuracy of observations of the Galilean satellites of Jupiter taken at the Abastumani Astrophysical Observatory of the Academy of Sciences of Georgia

The sets of photographic observations of the Galilean satellites of Jupiter taken at the Abastumani Astrophysical Observatory of the Academy of Sciences of Georgia are analyzed here. Positional observations of the system of Jupiter were made in the period from 1985 to 1994 with the use of the double Zeiss astrograph in order to determine the exact coordinates of Jupiter and its satellites. The accurate positions of the satellites and Jupiter itself, as well as their stellar (equatorial) coordinates relative to the stars of the currently available catalogs and the relative “satellite — satellite” coordinates were obtained from the observations. From the comparison of the observation results with the modern theories of motion of satellites, the accuracy in determining the positions of the satellites and Jupiter was analyzed. The results of observations are presented in the Pulkovo database of observations of Solar System bodies that is accessible to users at http://www.puldb.ru.

Linear high resolution dust mass spectrometer for a mission to the Galilean satellites

The discovery of volcanic activity on Enceladus stands out amongst the long list of findings by the Cassini mission to Saturn. In particular the compositional analysis of Enceladus ice particles by Cassini's Cosmic Dust Analyser (CDA) (Srama et al., 2004) has proven to be a powerful technique for obtaining information about processes below the moon's ice crust. Small amounts of sodium salts embedded in the particles' ice matrices provide direct evidence for a subsurface liquid water reservoir, which is, or has been, in contact with the moon's rocky core (Postberg et al., 2009, 2011b).Jupiter's Galilean satellites Ganymede, Europa, and Callisto are also believed to have subsurface oceans and are therefore prime targets for future NASA and ESA outer Solar System missions. The Galilean moons are engulfed in tenuous dust clouds consisting of tiny pieces of the moons' surfaces (Krüger et al., 1999), released by hypervelocity impacts of micrometeoroids, which steadily bombard the surfaces of the moons. In situ chemical analysis of these grains by a high resolution dust spectrometer will provide spatially resolved mapping of the surface composition of Europa, Ganymede, and Callisto, meeting key scientific objectives of the planned missions. However, novel high-resolution reflectron-type dust mass spectrometers (Sternovsky et al., 2007; Srama et al., 2007) developed for dust astronomy missions (Grün et al., 2009) are probably not robust enough to be operated in the energetic radiation environment of the inner Jovian system. In contrast, CDA's linear spectrometer is much less affected by harsh radiation conditions because its ion detector is not directly facing out into space. The instrument has been continuously operated on Cassini for 11 years. In this paper we investigate the possibility of operating a CDA-like instrument as a high resolution impact mass spectrometer. We show that such an instrument is capable of reliably identifying traces of organic and inorganic materials in the ice matrix of ejecta expected to be generated from the surfaces of the Galilean moons. These measurements are complementary, and in some cases superior, compared to other traditional techniques such as infrared remote sensing or in situ ion or neutral mass spectrometers.

Parametric excitation of gyroscopic waves in Thomson-Delaney cells of the ocean of Jovian moon Europa

A possible mechanism (of parametric resonance type) of excitation of planetary gyroscopic waves in Thomson-Delaney cells of the ocean of Jovian moon Europa is considered. It is assumed that the basis of this mechanism is a variation of liquid depth in a cell caused by tidal oscillations under the action of gravitational perturbing influence of Galilean satellites of Jupiter. Such a model leads to a system of linear differential equations with periodic coefficients of the Hill’s type. Under some additional assumptions it changes over into a system of independent Mathieu equations. The regions of parametric resonance of this system are constructed.

Compositional mapping of planetary moons by mass spectrometry of dust ejecta

Classical methods to analyze the surface composition of atmosphereless planetary objects from an orbiter are IR and gamma ray spectroscopy and neutron backscatter measurements. The idea to analyze surface properties with an in-situ instrument has been proposed by Johnson et al. (1998). There, it was suggested to analyze Europa's thin atmosphere with an ion and neutral gas spectrometer. Since the atmospheric components are released by sputtering of the moon's surface, they provide a link to surface composition. Here we present an improved, complementary method to analyze rocky or icy dust particles as samples of planetary objects from which they were ejected. Such particles, generated by the ambient meteoroid bombardment that erodes the surface, are naturally present on all atmosphereless moons and planets. The planetary bodies are enshrouded in clouds of ballistic dust particles, which are characteristic samples of their surfaces. In situ mass spectroscopic analysis of these dust particles impacting onto a detector of an orbiting spacecraft reveals their composition. Recent instrumental developments and tests allow the chemical characterization of ice and dust particles encountered at speeds as low as 1 km/s and an accurate reconstruction of their trajectories. Depending on the sampling altitude, a dust trajectory sensor can trace back the origin of each analyzed grain with about 10 km accuracy at the surface. Since the detection rates are of the order of thousand per orbit, a spatially resolved mapping of the surface composition can be achieved. Certain bodies (e.g., Europa) with particularly dense dust clouds, could provide impact statistics that allow for compositional mapping even on single flybys. Dust impact velocities are in general sufficiently high at orbiters about planetary objects with a radius >1000 km and with only a thin or no atmosphere. In this work we focus on the scientific benefit of a dust spectrometer on a spacecraft orbiting Earth's Moon as well as Jupiter's Galilean satellites. This ‘dust spectrometer' approach provides key chemical and isotopic constraints for varying provinces or geological formations on the surfaces, leading to better understanding of the body's geological evolution.

Report of the IAU Working Group on Cartographic Coordinates and Rotational Elements: 2009

Every three years the IAU Working Group on Cartographic Coordinates and Rotational Elements revises tables giving the directions of the poles of rotation and the prime meridians of the planets, satellites, minor planets, and comets. This report takes into account the IAU Working Group for Planetary System Nomenclature (WGPSN) and the IAU Committee on Small Body Nomenclature (CSBN) definition of dwarf planets, introduces improved values for the pole and rotation rate of Mercury, returns the rotation rate of Jupiter to a previous value, introduces improved values for the rotation of five satellites of Saturn, and adds the equatorial radius of the Sun for comparison. It also adds or updates size and shape information for the Earth, Mars’ satellites Deimos and Phobos, the four Galilean satellites of Jupiter, and 22 satellites of Saturn. Pole, rotation, and size information has been added for the asteroids (21) Lutetia, (511) Davida, and (2867) Steins. Pole and rotation information has been added for (2) Pallas and (21) Lutetia. Pole and rotation and mean radius information has been added for (1) Ceres. Pole information has been updated for (4) Vesta. The high precision realization for the pole and rotation rate of the Moon is updated. Alternative orientation models for Mars, Jupiter, and Saturn are noted. The Working Group also reaffirms that once an observable feature at a defined longitude is chosen, a longitude definition origin should not change except under unusual circumstances. It is also noted that alternative coordinate systems may exist for various (e.g. dynamical) purposes, but specific cartographic coordinate system information continues to be recommended for each body. The Working Group elaborates on its purpose, and also announces its plans to occasionally provide limited updates to its recommendations via its website, in order to address community needs for some updates more often than every 3 years. Brief recommendations are also made to the general planetary community regarding the need for controlled products, and improved or consensus rotation models for Mars, Jupiter, and Saturn.

THE LICK-CARNEGIE EXOPLANET SURVEY: A URANUS-MASS FOURTH PLANET FOR GJ 876 IN AN EXTRASOLAR LAPLACE CONFIGURATION

Continued radial velocity (RV) monitoring of the nearby M4V red dwarf star GJ 876 with Keck/High Resolution Echelle Spectrograph has revealed the presence of a Uranus-mass fourth planetary companion in the system. The new planet has a mean period of Pe = 126.6 days (over the 12.6-year baseline of the RV observations), and a minimum mass of mesin ie = 12.9 ± 1.7 M⊕. The detection of the new planet has been enabled by significant improvements to our RV data set for GJ 876. The data have been augmented by 36 new high-precision measurements taken over the past five years. In addition, the precision of all of the Doppler measurements have been significantly improved by the incorporation of a high signal-to-noise template spectrum for GJ 876 into the analysis pipeline. Implementation of the new template spectrum improves the internal rms errors for the velocity measurements taken during 1998–2005 from 4.1 m s−1 to 2.5 m s−1. Self-consistent, N-body fits to the RV data set show that the four-planet system has an invariable plane with an inclination relative to the plane of the sky of i = 59.°5. The fit is not significantly improved by the introduction of a mutual inclination between the planets “b” and “c,” but the new data do confirm a non-zero eccentricity, ed = 0.207 ± 0.055 for the innermost planet, “d.” In our best-fit coplanar model, the mass of the new component is me = 14.6 ± 1.7 M⊕. Our best-fitting model places the new planet in a three-body resonance with the previously known giant planets (which have mean periods of Pc = 30.4 and Pb = 61.1 days). The critical argument, φLaplace = λc − 3λb + 2λe, for the Laplace resonance librates with an amplitude of ΔφLaplace = 40° ± 13° about φLaplace = 0°. Numerical integration indicates that the four-planet system is stable for at least a billion years (at least for the coplanar cases). This resonant configuration of three giant planets orbiting an M dwarf primary differs from the well-known Laplace configuration of the three inner Galilean satellites of Jupiter, which are executing very small librations about φLaplace = 180° and which never experience triple conjunctions. The GJ 876 system, by contrast, comes close to a triple conjunction between the outer three planets once per every orbit of the outer planet, “e.”

Planetary gyroscopic waves in Thomson-Delaney cells of the ocean of Jupiter’s moon Europa

Observational data of the Galileo mission testify that there is a possibility of existence of planetary waves in the ocean of Jupiter’s moon Europa. A model of rotating ocean is used for the analysis of dynamics of underlying wavy processes. The model uses geometrical stratification of the ocean’s icy surface into separate cells with a typical size of order of 100 km. These cells of hydrothermal nature contain liquid lenses, and the possibility of their origination was postulated and theoretically studied by P. Thomson and J. Delaney in 2001. Using the Bubnov-Galerkin method, the spectrum of natural vibrations of liquid (gyroscopic waves) in Thomson-Delaney cells was found taking into account the satellite’s rotation in a simple model of the icy crust. In order to study a possibility of resonance excitation of tidal oscillations of liquid in the cells, the dominant elements of this spectrum are compared to theoretical values of the frequencies of tide-generating forces associated with eccentricity of the orbit of the Jupiter’s moon Europa and with perturbations from other Galilean satellites of Jupiter. This allows one to discover a large number of resonances on dominant modes with periods of from 3.5 to 7 days in the Europa ocean regions, corresponding to latitudes from 30° to 70°.

PLANET-PLANET SCATTERING IN PLANETESIMAL DISKS

We study the final architecture of planetary systems that evolve under the combined effects of planet-planet and planetesimal scattering. Using N-body simulations we investigate the dynamics of marginally unstable systems of gas and ice giants both in isolation and when the planets form interior to a planetesimal belt. The unstable isolated systems evolve under planet-planet scattering to yield an eccentricity distribution that matches that observed for extrasolar planets. When planetesimals are included the outcome depends upon the total mass of the planets. For M tot 1 MJ the final eccentricity distribution remains broad, whereas for M tot 1 MJ a combination of divergent orbital evolution and recircularization of scattered planets results in a preponderance of nearly circular final orbits. We also study the fate of marginally stable multiple planet systems in the presence of planetesimal disks, and find that for high planet masses the majority of such systems evolve into resonance. A significant fraction leads to resonant chains that are planetary analogs of Jupiter's Galilean satellites. We predict that a transition from eccentric to near-circular orbits will be observed once extrasolar planet surveys detect sub-Jovian mass planets at orbital radii of a 5-10 AU.

On a geometric method for determining the masses of the Galilean satellites of Jupiter

A geometric method for calculating the relative masses of the Galilean satellites of Jupiter is proposed. Local characteristics coincident with the Hausdorff—Bezikovich dimension have been calculated for each planet—satellite pair. The relative masses calculated by the geometric method differ from those obtained by analyzing the motion of spacecraft by no more than 0.1%.