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%.     

Astrometric results of observations of mutual occultations and eclipses of the Galilean satellites of Jupiter in 2002-2003

We suggest a new approach and develop an original method for deriving astrometric data from the photometry of mutual occultations and eclipses of planetary satellites. We decide to model not the relative apparent motion of one satellite with respect to another satellite but the deflection of the observed relative motion with respect to the theoretical motion implied by appropriate ephemerides.We have attempted to reduce the results of photometric observations of the Gallilean satellites during their mutual occultations and eclipses in 2002-2003. The data of observation for 319 light curves of 106 mutual events were received from the observers. The reliable 245 light curves were processed with our method. Eighty six apparent relative positions have been obtained.Systematic errors arise inevitably while deriving astrometric data. Most of them are due to factors that are unrelated to the methods for deriving astrometric data. The systematic errors are more likely due to incorrect excluding the effect of background on photometric counts. In the case of mutual occultations, the flux drop is determined to a considerable degree by the ratio of the mean albedos of the two satellites. Some mutual event observations revealed wrong adopted values of the mean albedos.     

Mutual occultations and eclipses of the Galilean satellites of Jupiter in 2002–2003: final astrometric results

The photometry of mutual occultations and eclipses of natural planetary satellites can be used to infer very accurate astrometric data. This can be achieved by processing the light curves of the satellites observed during international campaigns of photometric observations of these mutual events.
This work focuses on processing the complete data base of photometric observations of the mutual occultations and eclipses of the Galilean satellites made during the international campaign in 2002–2003. The final goal is to derive new accurate astrometric data.
We propose the most accurate photometric model of mutual events based on all the data available to date about the satellites, and develop the corresponding method for extracting astrometric data. This method is applied to derive astrometric data from photometric observations of mutual occultations and eclipses of the Galilean satellites.
We process the 371 light curves obtained during the international campaign of photometric observations of the Galilean satellites in 2002–2003. As compared with the theory, the rms 'O-C' residuals with respect to theory is equal to 0.055 and 0.064 arcsec in right ascension and declination, respectively, for the 274 best observations. Topocentric or heliocentric angular differences for satellite pairs are obtained for 119 time instants during the time period from 2002 October 10 to 2003 July 17.     

Oceans in the icy Galilean satellites of Jupiter?

Equilibrium models of heat transfer by heat conduction and thermal convection show that the three satellites of Jupiter—Europa, Ganymede, and Callisto—may have internal oceans underneath ice shells tens of kilometers to more than a hundred kilometers thick. A wide range of rheology and heat transfer parameter values and present-day heat production rates have been considered. The rheology was cast in terms of a reference viscosity ν₀ calculated at the melting temperature and the rate of change A of viscosity with inverse homologous temperature. The temperature dependence of the thermal conductivity k of ice I has been taken into account by calculating the average conductivity along the temperature profile. Heating rates are based on a chondritic radiogenic heating rate of 4.5 pW kg⁻¹ but have been varied around this value over a wide range. The phase diagrams of H₂O (ice I) and H₂O + 5 wt% NH₃ ice have been considered. The ice I models are worst-case scenarios for the existence of a subsurface liquid water ocean because ice I has the highest possible melting temperature and the highest thermal conductivity of candidate ices and the assumption of equilibrium ignores the contribution to ice shell heating from deep interior cooling. In the context of ice I models, we find that Europa is the satellite most likely to have a subsurface liquid ocean. Even with radiogenic heating alone the ocean is tens of kilometers thick in the nominal model. If tidal heating is invoked, the ocean will be much thicker and the ice shell will be a few tens of kilometers thick. Ganymede and Callisto have frozen their oceans in the nominal ice I models, but since these models represent the worst-case scenario, it is conceivable that these satellites also have oceans at the present time. The most important factor working against the existence of subsurface oceans is contamination of the outer ice shell by rock. Rock increases the density and the pressure gradient and shifts the triple point of ice I to shallower depths where the temperature is likely to be lower then the triple point temperature. According to present knowledge of ice phase diagrams, ammonia produces one of the largest reductions of the melting temperature. If we assume a bulk concentration of 5 wt% ammonia we find that all the satellites have substantial oceans. For a model of Europa heated only by radiogenic decay, the ice shell will be a few tens of kilometers thinner than in the ice I case. The underlying rock mantle will limit the depth of the ocean to 80-100 km. For Ganymede and Callisto, the ice I shell on top of the H₂O-NH₃ ocean will be around 60- to 80-km thick and the oceans may be 200- to 350-km deep. Previous models have suggested that efficient convection in the ice will freeze any existing ocean. The present conclusions are different mainly because they are based on a parameterization of convective heat transport in fluids with strongly temperature dependent viscosity rather than a parameterization derived from constant-viscosity convection models. The present parameterization introduces a conductive stagnant lid at the expense of the thickness of the convecting sublayer, if the latter exists at all. The stagnant lid causes the temperature in the sublayer to be warmer than in a comparable constant-viscosity convecting layer. We have further modified the parameterization to account for the strong increase in homologous temperature, and therefore decrease in viscosity, with depth along an adiabat. This modification causes even thicker stagnant lids and further elevated temperatures in the well-mixed sublayer. It is the stagnant lid and the comparatively large temperature in the sublayer that frustrates ocean freezing.     

Polarization opposition effect for the Galilean satellites of Jupiter

We present results of polarimetric observations of the Galilean satellites Io, Europa, Ganymede, and Callisto at phase angles ranging from 0.19° to 2.22°. The observations in the UBVR filters were performed using a one-channel photoelectric polarimeter attached to 70-cm telescope of the Chuguev Observation Station (Ukraine) on November 19-December 7, 2000. We have observed the polarization opposition effect for Io, Europa, and Ganymede to be a sharp secondary spike of negative polarization with an amplitude of about −0.4% centered at phase angles of 0.2°-0.7° and superimposed on the regular negative polarization branch. Although these minima for Io, Europa, and Ganymede show many similarities, they also exhibit a number of distinctions. The polarization opposition effect appears to be wavelength-dependent, at least for Europa and Ganymede. No polarization opposition effect was found for Callisto. The results obtained are discussed within the framework of different mechanisms of light scattering.     

Three-body capture of irregular satellites: Application to Jupiter

We investigate a new theory of the origin of the irregular satellites of the giant planets: capture of one member of a ∼100-km binary asteroid after tidal disruption. The energy loss from disruption is sufficient for capture, but it cannot deliver the bodies directly to the observed orbits of the irregular satellites. Instead, the long-lived capture orbits subsequently evolve inward due to interactions with a tenuous circumplanetary gas disk.We focus on the capture by Jupiter, which, due to its large mass, provides a stringent test of our model. We investigate the possible fates of disrupted bodies, the differences between prograde and retrograde captures, and the effects of Callisto on captured objects. We make an impulse approximation and discuss how it allows us to generalize capture results from equal-mass binaries to binaries with arbitrary mass ratios.We find that at Jupiter, binaries offer an increase of a factor of ∼10 in the capture rate of 100-km objects as compared to single bodies, for objects separated by tens of radii that approach the planet on relatively low-energy trajectories. These bodies are at risk of collision with Callisto, but may be preserved by gas drag if their pericenters are raised quickly enough. We conclude that our mechanism is as capable of producing large irregular satellites as previous suggestions, and it avoids several problems faced by alternative models.     

Cassini VIMS observations of the Galilean satellites including the VIMS calibration procedure

The Visual and Infrared Mapping Spectrometer (VIMS) observed the Galilean satellites during the Cassini spacecraft's 2000/2001 flyby of Jupiter, providing compositional and thermal information about their surfaces. The Cassini spacecraft approached the jovian system no closer than about 126 Jupiter radii, about 9 million kilometers, at a phase angle of <90°, resulting in only sub-pixel observations by VIMS of the Galilean satellites. Nevertheless, most of the spectral features discovered by the Near Infrared Mapping Spectrometer (NIMS) aboard the Galileo spacecraft during more than four years of observations have been identified in the VIMS data analyzed so far, including a possible ¹³C absorption. In addition, VIMS made observations in the visible part of the spectrum and at several new phase angles for all the Galilean satellites and the calculated phase functions are presented. In the process of analyzing these data, the VIMS radiometric and spectral calibrations were better determined in preparation for entry into the Saturn system. Treatment of these data is presented as an example of the VIMS data reduction, calibration and analysis process and a detailed explanation is given of the calibration process applied to the Jupiter data.     

The icy Galilean satellites: ultraviolet phase curve analysis

Ultraviolet disk-integrated solar phase curves of the icy galilean satellites Europa, Ganymede, and Callisto are presented, using combined data sets from the International Ultraviolet Explorer (IUE), Hubble Space Telescope (HST), and the Galileo Ultraviolet Spectrometer. Global, disk-integrated solar phase curves for all three satellites, in addition to disk-integrated solar phase curves for Europa's leading, trailing, jovian, and anti-jovian hemispheres, are modeled using Hapke's equations for 7 broadband UV wavelengths between 260 and 320 nm. The sparse coverage in solar phase angle, particularly for Ganymede and Callisto, and the noise in the data sets poorly constrain some of the photometric parameter values in the model. However, the results are sufficient for forming a preliminary relationship between the effects of particle bombardment on icy surfaces and photometric scattering properties at ultraviolet wavelengths. Callisto exhibits a large UV opposition surge and a surface comprised of relatively low-backward scattering particles. Europa's surface displays a dichotomy between the jovian and anti-jovian hemispheres (the anti-jovian hemisphere is more backward scattering), while a less pronounced hemispherical variation was detected between the leading and trailing hemispheres. Europa's surface, with the exception of the trailing hemisphere region, appears to have become less backscattering between the late-1970s-early-1980s and the mid-1990s. These results are commensurate with the bombardment history of these surfaces by magnetospheric charged particles.     

Equipotential surface and normal gravity of the Galilean satellites

In this article, expanded equations of normal gravity on the equipotential surface are proposed for a natural satellite whose orbital plane is close to its equatorial plane. Tidal effects on the normal gravity are also discussed. The authors apply these to the Galilean satellites. Calculations suggest that the tides raised by Jupiter weakly affect the Galilean satellites. The radial displacements of the gravity due to the tides are in the range between 10⁻³ and 10⁻⁵ m s⁻², which are similar to the latitudinal and longitudinal displacements. The variations along the latitude circle are larger than those along the longitude circle. We conclude that the tidal effects on most of the Galilean satellites are larger than those on the Moon.     

Physisorption of CO2 on non-ice materials relevant to icy satellites

CO₂ is known to adsorb onto clay and other minerals when a significant atmospheric pressure is present. We have found that CO₂ can also adsorb onto some clays when the CO₂ partial pressure is effectively zero under ultra-high vacuum (UHV) if cooled to the surface temperatures of the icy satellites of Jupiter and Saturn. The strength of adsorption and the spectral characteristics of the adsorbed CO₂ infrared (IR) ν₃ absorption band near 4.25 μm depend on the composition and temperature of the adsorbent. CO₂ remains adsorbed onto the clay mineral montmorillonite for >10 s of min when exposed to a vacuum of ∼1×¹⁰⁻⁸ Torr at ∼125 K. CO₂ does not adsorb onto serpentine, goethite, or palagonite under these conditions. A small amount may adsorb onto kaolinite. When heated above 150 K under vacuum, the CO₂ desorbs from the montmorillonite within a few minutes. The ν₃ absorption band of CO₂ adsorbed onto montmorillonite at 125 K is similar to that of the CO₂ detected on the saturnian and Galilean satellites and is markedly different from CO₂ adsorbed onto montmorillonite at room temperature. We infer the adsorption process is physisorption and postulate that this mechanism may explain the presence and spectral characteristics of the CO₂ detected in the surfaces of these outer satellites.     

Free and forced obliquities of the Galilean satellites of Jupiter

The obliquity, or angular separation between orbit normal and spin pole, is an important parameter for the geodynamics of most Solar System bodies. Tidal dissipation has driven the obliquities of the Galilean satellites of Jupiter to small, but non-zero values. We present estimates of the free and forced obliquities of these satellites using a simple secular variation model for the orbits, and spin pole precession rate estimates based on gravity field parameters derived from Galileo spacecraft encounters. The free obliquity values are not well constrained by observations, but are presumed to be very small. The forced obliquity variations depend only on the orbital variations and the spin pole precession rate parameters, which are quite well known. These variations are large enough to influence spatial and temporal patterns of tidal dissipation and tidal stress.     

A new theory of the motions of the Galilean satellites of Jupiter

The main features of this theory are presented with special emphasis on the most specific of them: choice of the parameters, separation of the problem into subproblems (main problem, generalized main problem, complete problem), special adaptation of the method required by the resonant situation of the Galilean system.     

Temporal behavior of the SO 1.707 μm ro-vibronic emission band in Io's atmosphere

We report observations of the ro-vibronic a¹Δ→X³Σ⁻ transition of SO at 1.707 μm on Io. These data were taken while Io was eclipsed by Jupiter, on four nights between July 2000 and March 2003. We analyze these results in conjunction with a previously published night to investigate the temporal behavior of these emissions. The observations were all conducted using the near-infrared spectrometer NIRSPEC on the W.M. Keck II telescope. The integrated emitted intensity for this band varies from 0.8×¹⁰²⁷ to 2.4×¹⁰²⁷ photons/s, with a possible link to variations in Loki's infrared brightness. The band-shapes imply rotational temperatures of 550-1000 K for the emitting gas, lending further evidence to a volcanic origin for sulfur monoxide. An attempt to detect the B¹Σ→X³Σ⁻ transition of SO at 0.97 μm was unsuccessful; simultaneous detection with the 1.707 μm band would permit determination of the SO column abundance.     

Librations of the Galilean satellites: The influence of global internal liquid layers

The four Galilean satellites are thought to harbor one or even two global internal liquid layers beneath their surface layer. The iron core of Io and Ganymede is most likely (partially) liquid and also the core of Europa may be liquid. Furthermore, there are strong indications for the existence of a subsurface ocean in Europa, Ganymede, and Callisto. Here, we investigate whether libration observations can be used to prove the existence of these liquid layers and to constrain the thickness of the overlying solid layers. For Io, the presence of a small liquid core increases the libration of the mantle by a few percent with respect to an entirely solid Io and mantle libration observations could be used to determine the mantle thickness with a precision of several tens of kilometers given that the libration amplitude can be measured with a precision of 1 m. For Europa, Ganymede, and Callisto, the presence of a water ocean close to the surface increases by at least an order of magnitude the ice shell libration amplitude with respect to an entirely solid satellite. The shell libration depends essentially on the shell thickness and to a minor extent on the density difference between the ocean and the ice shell. The possible presence of a liquid core inside Europa and Ganymede has no noticeable influence on their shell libration. For a precision of several meters on the libration measurements, in agreement with the expected accuracy with the NASA/ESA EJSM orbiter mission to Europa and Ganymede, an error on the shell thickness of a few tens kilometers is expected. Therefore, libration measurements can be used to detect liquid layers such as Io’s core or water subsurface oceans in Europa, Ganymede, and Callisto and to constrain the thickness of the overlying solid surface layers.     

A model for the temperature-dependence of tidal dissipation in convective plumes on icy satellites: Implications for Europa and Enceladus

To explain the formation of surface features on Europa, Enceladus, and other satellites, many authors have postulated the spatial localization of tidal heating within convective plumes. However, the concept that enhanced tidal heating can occur within a convective plume has not been rigorously tested. Most models of this phenomenon adopt a tidal heating with a temperature-dependence derived for an incompressible, homogeneous (zero-dimensional) Maxwell material, but it is unclear whether this formulation is relevant to the heterogeneous situation of a warm plume surrounded by cold ice. To determine whether concentrated dissipation can occur in convective plumes, we develop a two-dimensional model to compute the volumetric dissipation rate for an idealized, vertically oriented, isolated convective plume obeying a Maxwellian viscoelastic compressible rheology. We apply the model to the Europa and Enceladus ice shells, and we investigate the consequences for partial melting and resurfacing processes on these bodies. We find that the tidal heating is strongly temperature dependent in a convective ice plume and could produce elevated temperatures and local partial melting in the ice shells of Europa and Enceladus. Our calculation provides the first quantitative verification of the hypothesis by Sotin et al. [Sotin, C., Head, J.W., Tobie, G., 2002. Geophys. Res. Lett. 29. 74-1] and others that the tidal dissipation rate is a strong function of temperature inside a convective plume. On Europa, such localized heating could help allow the formation of domes and chaos terrains by convection. On Enceladus, localized tidal heating in a thermal plume could explain the concentrated activity at the south pole and its associated heat transport of 2-7 GW.     

Time-dependent flexure of the lithospheres on the icy satellites of Jupiter and Saturn

Previous analyses into flexural deformation on the icy satellites of Jupiter and Saturn have assumed static, elastic lithospheres. Viscous creep within the lithosphere, however, can cause evolution over time. Here, we apply a finite-element model that employs a time-dependent elastic–viscous-plastic rheology in order to investigate flexure on icy satellites. Factors that affect this time-dependent response are those that control creep rates; surface temperature, heat flow, and grain size. Our results show that surface temperature is by far the dominant factor. At higher surface temperatures (100–130 K), the evolution of the deformation is such that the thickness of a modeled elastic lithosphere could vary by up to an order of magnitude, depending on the time scale over which the deformation occurred. Because the flexure observed on icy satellites generally indicates transient high heat flow events, our results indicate that the duration of the heat pulse is an important factor. For the icy worlds of Jupiter and Saturn, static models of lithospheric flexure should be used with caution.     

Models,figures, and gravitational moments of the Galilean satellites of Jupiter and icy satellites of Saturn

A general theory for the figures of satellites, which are synchronously rotating in the gravitational field of a planet, is developed to the first approximation. Love numbers, figure parameters, and gravitational moments for two- and three-layer models of the Galilean satellites, Titan, and Saturn's icy satellites are calculated. With the assumed accuracy for flyby measurements of gravitational moments it should be possible to determine the degree of differentiation of Ganymede. The differences between equatorial a and polar c semiaxes, as derived from the observational data, appear to be exaggerated for Io and Mimas (although better agreement between calculated and observed values of (a?c) could be obtained if this satellite had a larger mass). For Enceladus the observed value of (a?c) is in satisfactory agreement with calculations, based on different types of trial models. However, in order to discriminate between different Enceladus trial models, it is necessary to determine the figure parameters more precisely.     

The eruptive evolution of the Galilean satellites: Implications for the ancient magnetic field of Jupiter

The hypothesis considering the Jupiter-Sun system as a limiting case of a close binary star implies the initial relative ice abundances in all the Galilean satellites to be essentially equal. The satellites move in the Jovian magnetosphere; thus the unipolar current flowing through their bodies subjected their ices to volumetric electrolysis. Explosions of the electrolysis products resulted in a loss of ices. While Callisto did not explode at all, Ganymede exploded once, Europa twice, and Io two or three times. An analysis of the magnetic field changes needed to create the modern ice abundances in the satellite shows:

1. the initial field of Jupiter was ～10² times stronger when compared with the present-day field, and
2. the field had to decrease exponentially with τ_2| ≈ (0.6?1), which means its relic nature.

     

彗木相撞中的惯性引力波

苏梅克-列维9号彗星(SL9)与木星相撞后，在木星上观测到的以常速度(～450m／s)向外扩展的圆环意味着这是碰撞在木星大气中引起的线性波动．我们选取：非旋转、无粘性、密度分层、不可压缩的木星大气模型，而且木星大气以水平速度U=b az运动；给出初始扰动压力P(r；0)作为碰撞的初始条件，用流体力学方程组求解了彗木相撞中的惯性引力波．结果表明：当木星大气以速度U=U0(～170m／s)运动时，彗星碎片的大部分能量都用来产生内波，同时还得到彗星碎片的撞击深度H与水平相速Vp的关系式．当木星大气以速度为U=b az运动时，木星大气的扰动能量不再是在动能和势能间均分。     

Mutual occultations and eclipses of the Galilean satellites of Jupiter in 1997: Astrometric results of observations

In 2006, a complete database of the international campaign on photometric observations of the Galilean satellites of Jupiter in the 1997 epoch of mutual occultations and eclipses was published. Only two thirds of the observations were considered by other authors beforehand. In this study, we have processed the whole observational database with an original technique in order to obtain the astrometric data. We determined 301 relative positions of the satellites from photometric observations performed at 50 observatories around the world. The results are put into a common database of all observations of the natural planetary satellites called the Natural Satellites Data Center (NSDC) available on the Internet site http://www.sai.msu.ru/neb/nss/index.htm. The influence of random and systematic errors on the accuracy of determining the coordinates of satellites has been analyzed. It has been shown that the largest systematic errors are caused by inaccurate elimination of the background of the photometric measurements and by the erroneous data on the albedo of satellites. The actual accuracy of astrometric results is 0.05″ and 0.07″ in right ascension and declination, respectively. New recommendations for photometric observations of satellites during the considered phenomena have been developed in order to avoid the systematic errors.