Search

The advanced Russian project Laplace-P is aimed at developing and launching two scientific spacecraft (SC)--Laplace-P1 (LP1 SC) and Laplace-P2 (LP2 SC)--designed for remote and in-situ studies of the system of Jupiter and its moon Ganymede. The LP1 and LP2 spacecraft carry an orbiter and a lander onboard, respectively. One of the orbiter's objectives is to map the surface of Ganymede from the artificial satellite's orbit and to acquire the data for the landing site selection. The main objective of the lander is to carry out in-situ investigations of Ganymede's surface. The paper describes the scientific goals and objectives of the mission, its special features, and the LP1 and LP2 mission profiles during all of the phases--from the launch to the landing on the surface of Ganymede. [ABSTRACT FROM AUTHOR]

In this contribution, an efficient technique to design direct (i.e., without intermediate flybys) low-energy trajectories in multi-moon systems is presented. The method relies on analytical two-body approximations of trajectories originating from the stable and unstable invariant manifolds of two coupled circular restricted three-body problems. We provide a means to perform very fast and accurate computations of the minimum-cost trajectories between two moons. Eventually, we validate the methodology by comparison with numerical integrations in the three-body problem. Motivated by the growing interest in the robotic exploration of the Jovian system, which has given rise to numerous studies and mission proposals, we apply the method to the design of minimum-cost low-energy direct trajectories between Galilean moons, and the case study is that of Ganymede and Europa. [ABSTRACT FROM AUTHOR]

Jupiter's satellites are subject to strong tidal forces which result in variations of the gravitational potential and deformations of the satellites' surfaces on the diurnal tidal cycle. Such variations are described by the Love numbers $$k_2$$ and $$h_2$$ for the tide-induced potential variation due to internal mass redistribution and the radial surface displacement, respectively. The phase-lags $$ \phi _{k_2}$$ and $$ \phi _{h_2}$$ of these complex numbers contain information about the rheological and dissipative states of the satellites. Starting from interior structure models and assuming a Maxwell rheology to compute the tidal deformation, we calculate the phase-lags in application to Ganymede and Europa. For both satellites we assume a decoupling of the outer ice-shell from the deep interior by a liquid subsurface water ocean. We show that, in this case, the phase-lag difference $$\varDelta \phi = \phi _{k_2}- \phi _{h_2}$$ can provide information on the rheological and thermal state of the deep interiors if the viscosities of the deeper layers are small. In case of Ganymede, phase-lag differences can reach values of a few degrees for high-pressure ice viscosities $${<}10^{14}$$ Pa s and would indicate a highly dissipative state of the deep interior. In this case $$\varDelta \phi $$ is dominated by dissipation in the high-pressure ice layer rather than dissipation within the ice-I shell. These phase lags would be detectable from spacecraft in orbit around the satellite. For Europa $$\varDelta \phi $$ could reach values exceeding $$20^\circ $$ and phase-lag measurements could help distinguish between (1) a hot dissipative silicate mantle which would in thermal equilibrium correspond to a very thin outer ice-I shell and (2) a cold deep interior implying that dissipation would mainly occur in a thick (several tens of km) outer ice-I shell. These measurements are highly relevant for ESA's Jupiter Icy Moons Explorer (JUICE) and NASA's Europa Multiple Flyby Mission, both targeted for the Jupiter system. [ABSTRACT FROM AUTHOR]

The new technique for generation of coordinate control point networks based on photogrammetric processing of heterogeneous planetary images (obtained at different time, scale, with different illumination or oblique view) is developed. The technique is verified with the example for processing the heterogeneous information obtained by remote sensing of Ganymede by the spacecraft Voyager-1, -2 and Galileo. Using this technique the first 3D control point network for Ganymede is formed: the error of the altitude coordinates obtained as a result of adjustment is less than 5 km. The new control point network makes it possible to obtain basic geodesic parameters of the body (axes size) and to estimate forced librations. On the basis of the control point network, digital terrain models (DTMs) with different resolutions are generated and used for mapping the surface of Ganymede with different levels of detail (Zubarev et al., 2015b). [ABSTRACT FROM AUTHOR]

The paper discusses the formation and dynamics of the rarefied gas envelope near the icy surface of Jupiter's moon Ganymede. Being the most massive icy moon, Ganymede can form a rarefied exosphere with a relatively dense near-surface layer. The main parent component of the gas shell is water vapor, which enters the atmosphere due to thermal degassing, nonthermal radiolysis, and other active processes and phenomena on the moon's icy surface. A numerical kinetic simulation is performed to investigate, at the molecular level, the formation, chemical evolution, and dynamics of the mainly HO- and O-dominant rarefied gas envelopes. The ionization processes in these rarefied gas envelopes are due to exposure to ultraviolet radiation from the Sun and the magnetospheric plasma. The chemical diversity of the icy moon's gas envelope is attributed to the primary action of ultraviolet solar photons and plasma electrons on the rarefied gas in the HO- or O-dominant atmosphere. The model is used to calculate the formation and development of the chemical diversity in the relatively dense near-surface envelope of Ganymede, where an important contribution comes from collisions between parent molecules and the products of their photolysis and radiolysis. [ABSTRACT FROM AUTHOR]

Employing multiple gravity-assist flybys of Jupiter's Galilean moons can save a substantial amount of $$\varDelta V$$ when capturing into orbit about Jupiter. Using Callisto and Ganymede, the most massive and distant of the Galilean moons, as gravity-assist bodies reduces the Jupiter orbit insertion $$\varDelta V$$ cost, while allowing the spacecraft to remain above the worst of Jupiter's radiation belts. A phase-angle approach is used to find initial guesses for a Lambert targeter to find patched-conic Callisto-Ganymede transfers. A B-plane targeter using grid search methodology is used to backward target Earth to find launch conditions. Twenty-nine distinct patched-conic trajectories were found from Earth to Callisto-Ganymede-JOI capture throughout the search space from 2020-2060. Five promising trajectories were found that launch from Earth between July 11, 2023 and July 20, 2023, and arrive at Jupiter between February and September 2026. These trajectories were numerically integrated using GMAT and, in the author's opinion, are excellent candidates for use on NASA's planned Europa Clipper mission. [ABSTRACT FROM AUTHOR]

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) = 0.040″ and (O-C) =-0.053″ assuming the normal distribution law. [ABSTRACT FROM AUTHOR]

The aurora on Ganymede results from the interaction of Jovian plasma disk electrons with Ganymede's tenuous atmosphere. At the same time, the electrons surrounding Ganymede have energy insufficient for the excitation of emission in the observed lines. They can acquire the necessary acceleration through various processes, such as reconnection of Ganymede's intrinsic magnetic field with the Jovian magnetic field in the upstream and downstream regions. The generation mechanism of a field-aligned potential drop on auroral field lines is considered. The lack of charge carriers required for the generation of the necessary current closing the Alfvén-wing field-aligned currents is shown to be responsible for the formation of an accelerating potential and the acceleration of thermal magnetospheric electrons. The total current in the circuit is determined by the calculated cross-field potential drop applied to Ganymede and by the Pedersen conductivity of Ganymede's ionosphere. [ABSTRACT FROM AUTHOR]

Jupiter's moon-Ganymede-is the largest satellite in our solar system. Galileo spacecraft made six close flybys to explore Ganymede. More information was acquired about particle population, magnetic field and plasma waves during these encounters. In this paper, our aim is to study the generation of electrostatic electron cyclotron harmonic (ECH) emissions in the vicinity of Ganymede using the observed particle data. The calculated ECH wave's growth rates are analyzed in the light of observations of plasma waves along the path of Galileo near Ganymede. Dispersion relation for electrostatic mode is solved to obtain the temporal growth rates. A new electron distribution function, fitted to distribution observed near Ganymede, is used in the calculations. A parametric study is performed to evaluate the effect of loss-cone angle and the ratio of plasma to gyro-frequency on growth rates. It is found that ECH waves growth rates generally decrease as the loss-cone angle is increased. However, the ratio plasma to gyro-frequency has almost no effect on the growth rates. These parameters vary considerably along the Galileo trajectory near Ganymede. This is the first study which relates the occurrence of ECH waves with the particle and magnetic field data in the vicinity of Ganymede. The study of ECH wave growth rate near Ganymede is important for the calculation of pitch angle scattering rates of low-energy electrons and their subsequent precipitation into the thin atmosphere of Ganymede producing ultraviolet emissions. Results of the present study may also be relevant for the upcoming JUNO and JUICE missions to Jupiter. [ABSTRACT FROM AUTHOR]

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 (Fe and Fe) 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). [ABSTRACT FROM AUTHOR]

The magnetic field of a planet or a planetary moon contains contributions from a variety of sources in the environment of the body (external sources) and its interior (internal sources). This chapter describes different methods that have been developed for the separation of external and internal source contributions, and their application to selected planets and one of Jupiter’s moons, Ganymede. [ABSTRACT FROM AUTHOR]

Electromagnetic induction is a powerful technique to study the electrical conductivity of the interior of the Earth and other solar system bodies. Information about the electrical conductivity structure can provide strong constraints on the associated internal composition of planetary bodies. Here we give a review of the basic principles of the electromagnetic induction technique and discuss its application to various bodies of our solar system. We also show that the plasma environment, in which the bodies are embedded, generates in addition to the induced magnetic fields competing plasma magnetic fields. These fields need to be treated appropriately to reliably interpret magnetic field measurements in the vicinity of solar system bodies. Induction measurements are particularly important in the search for liquid water outside of Earth. Magnetic field measurements by the Galileo spacecraft provide strong evidence for a subsurface ocean on Europa and Callisto. The induction technique will provide additional important constraints on the possible subsurface water, when used on future Europa and Ganymede orbiters. It can also be applied to probe Enceladus and Titan with Cassini and future spacecraft. [ABSTRACT FROM AUTHOR]

Of the terrestrial planets, Earth and Mercury have self-sustained fields while Mars and Venus do not. Magnetic field data recorded at Ganymede have been interpreted as evidence of a self-generated magnetic field. The other icy Galilean satellites have magnetic fields induced in their subsurface oceans while Io and the Saturnian satellite Titan apparently are lacking magnetic fields of internal origin altogether. Parts of the lunar crust are remanently magnetized as are parts of the crust of Mars. While it is widely accepted that the magnetization of the Martian crust has been caused by an early magnetic field, for the Moon alternative explanations link the magnetization to plasma generated by large impacts. The necessary conditions for a dynamo in the terrestrial planets and satellites are the existence of an iron-rich core that is undergoing intense fluid motion. It is widely accepted that the fluid motion is caused by convection driven either by thermal buoyancy or by chemical buoyancy or by both... [ABSTRACT FROM AUTHOR]

The processes of the formation and dynamics of tenuous gaseous envelopes of icy moons in giant-planet systems are considered. Tenuous exospheres with relatively dense surface layers are likely to form around more massive icy satellites, such as, for example, the Galilean satellites Europa and Ganymede in the Jovian system. Escaping exospheres are formed in the case of low-mass icy moons, as happens for the icy satellite Enceladus in the Saturnian system. The main parent component of such gaseous envelopes is water vapor, which enters into the atmosphere as a result of thermal degassing processes, nonthermal radiolysis, and other active processes and phenomena on the icy surface of a satellite. A numerical kinetic model has been developed to study on a molecular level the processes of the formation, chemical evolution, and dynamics of tenuous gaseous envelopes dominated mainly by H2O. The ionization processes in such tenuous gaseous envelopes are caused by solar ultraviolet (UV) radiation and solar-wind and/or magnetospheric plasma. The primary processes when ultraviolet solar photons and plasma electrons affect the tenuous gas of the H2O-dominated atmosphere are responsible for the chemical diversity of the gaseous envelopes of icy moons. Ionization chemistry, including ion-molecular reactions, dissociative recombination of molecular ions, and the reactions of the charge exchange with magnetospheric ions, is important for the formation of chemical diversity in gaseous envelopes of icy satellites. The model considered in the study was used to numerically simulate the formation and development of chemical diversity in the tenuous gaseous envelope of Enceladus. The numerical results were compared to the direct Cassini measurements during its close flyby near Enceladus. [ABSTRACT FROM AUTHOR]

The possibility of an explosive mechanical instability of ice (the Bridgman effect) in the thick icy shells of Jupiter’s and Saturn’s satellites is discussed in principle. The Bridgman effect is an explosive instability of dielectric solid bodies, which disintegrate into microscopic fragments under a quasistatic uniaxial loading in open compression systems at high pressures. The explosive instabilities of ice recently discovered in laboratory experiments with the Bridgman effect are also expected to occur in the extensive deep layers of the shells of icy planetary satellites (for example, in the case of episodical formation of major cracks in their lithospheres due to tidal forces, nonsynchronous rotation of the satellites, or extremely powerful impacts). The depths of occurrence of mechanically unstable ice in the thick crusts of Ganymede, Europa, and Titan, taken as examples, are crudely estimated using a pure-ice model without a possible ammonia admixture. The estimated thickness of the explosive-instability zone in the icy crust of Ganymede (under the assumption that the crust is ∼75 km thick) ranges from ∼7 to ∼27 km at depths from ∼40 to ∼67 km, depending on the scaling parameter E = 0.2–1. This parameter relates the experimentally determined thicknesses of the ice samples in which the Bridgman effect occurs under laboratory conditions to the expected thicknesses of the explosively unstable layers in the envelopes of the icy satellites. Explosive effects are possible not throughout the entire thickness of the unstableice layer but only within some part of it, several centimeters to several tens of meters in thickness. According to the estimated location of the unstable layer in the crust of Europa (for an assumed crust thickness of ∼30 km), such a layer can exist only at scaling factors E < 0.6 at depths ranging from ∼21 to ∼28 km. For Titan, if its crust is ∼100 km thick, the thickness of the unstable layer is similarly estimated to range from ∼15 to ∼55 km at depths from ∼37 to ∼92 km for a scaling parameter E lying within the range 0.2–1. At E 0.2, which is quite possible, explosive instabilities of ice could also be expected on the Earth, in the icy shells of Antarctica and Greenland at depths from ∼1 to ∼1.5 km. [ABSTRACT FROM AUTHOR]

Reports digital elevation models of parts of the surface of Ganymede, derived from stereo pairs combining data from the Voyager and Galileo spacecraft, which reveal bright, smooth terrains that lie at roughly constant elevations 100 to 1,000 meters below the surrounding rougher terrains. Indication that the smooth terrains were formed by flooding by low-viscosity water-ice lavas; Speculation on the formation of bright terrain; Topic of volcanism.

Reports the discovery , during the spacecraft Galileo's encounters with Ganymede, of an internal magnetic field. The impact of Ganymede's magnetic field upon Jupiter's magnetosphere; The lack of identification of a source.

Io is the volcanically most active body in the Solar System and has a large surface heat flux. The geological activity is thought to be the result of tides raised by Jupiter, but it is not known whether the current tidal heat production is sufficiently high to generate the observed surface heat flow. Io’s tidal heat comes from the orbital energy of the Io–Jupiter system (resulting in orbital acceleration), whereas dissipation of energy in Jupiter causes Io’s orbital motion to decelerate. Here we report a determination of the tidal dissipation in Io and Jupiter through its effect on the orbital motions of the Galilean moons. Our results show that the rate of internal energy dissipation in Io (k2/Q = 0.015 ± 0.003, where k2 is the Love number and Q is the quality factor) is in good agreement with the observed surface heat flow, and suggest that Io is close to thermal equilibrium. Dissipation in Jupiter (k2/Q = (1.102 ± 0.203) × 10-5) is close to the upper bound of its average value expected from the long-term evolution of the system, and dissipation in extrasolar planets may be higher than presently assumed. The measured secular accelerations indicate that Io is evolving inwards, towards Jupiter, and that the three innermost Galilean moons (Io, Europa and Ganymede) are evolving out of the exact Laplace resonance. [ABSTRACT FROM AUTHOR]

Presents research which measured submicrometer dust within a few radii of Jupiter's satellite Ganymede. Concentrations of dust in the ring systems of planets and along planetary orbits; Generation of individual dust grains; Directions, speeds and distribution of masses indicating dust from Ganymede; Ejection process resulting from hypervelocity impacts of dust onto Ganymede's surface; Dust near Callisto and Europa.

Focuses on the signature of condensed molecular oxygen which has been reported in optical-reflectance measurements of the jovian moon Ganymede. Tenous oxygen atmosphere observed on Europa; The surfaces of the moons which contain large amounts of water ice; Data of Lanzerotti et al; Laboratory measurements of the threshold energy, cross-section and temperature dependence of O2 production by electronic excitation of ice in vacuum; Findings; Conclusions.

Reports measurements by the Galileo spacecraft of Ganymede's overall density and the spherical harmonics of its gravitational field. The demonstration that Ganymede has differentiated into a core and mantle; The suggestion of a small metallic core; The similarities to Io.

Reports measurements of plasma waves and radio emissions from Galileo's first encounter with Ganymede. The detection of intense plasma waves over a region of space four times Ganymede's diameter; The suggestion that Ganymede has a large, extended magnetosphere.

Discusses the question of how the young ice on the surface of the satellite of Jupiter, Ganymede, formed. Divergent theories that the young ice formed through either icy volcanism or tectonic activity; Study published in the March 1, 2001 issue of 'Nature' magazine which used images from the spacecrafts Voyager and Galileo in its proposal that the smooth areas of icy terrain are the result of resurfacing through icy volcanism, whereas the higher-standing, heavily fractured regions were resurfaced tectonically.

Provides background and analysis for a series of papers concerning discoveries from Galileo's mission around Ganymede. Ganymede's status as being Jupiter's largest moon; The surprising discovery of Ganymede's substantial magnetic field; The four papers found in the December 12, 1996 issue of `Nature.'

Opinion. Argues that Ganymede has an outer silicate core surrounding a liquid (or partially liquid) inner core of iron or iron sulfide. The possible explanation for how the magnetic field is generated; The implications for Io; The study of data about Ganymede taken from the Galileo space probe.

Relates data about the surface of the Jovian moon Ganymede, from the Galileo spacecraft's fly-by in June 1996. Flying within 7,500 kilometers of the largest moon of Jupiter; Release of the first pictures in July 1996; Surprise that the moon has more complicated tectonic processes than expected; Additional surprise, that Ganymede has a magnetic field.