Satellites Of Jupiter Research Articles

Early Stages of Galilean Moon Formation in a Water-depleted Environment

A key feature of the Galilean satellite system is its monotonic decrease in bulk density with growing distance from Jupiter, indicating an ice mass fraction that is zero in the innermost moon Io and about half in the outer moons Ganymede and Callisto. Jupiter-formation models, and perhaps the Juno spacecraft water measurements, are consistent with the possibility that the Jovian system may have formed, at least partly, from ice-poor material. And yet, models of the formation of the Galilean satellites usually assume abundant water ice in the system. Here, we investigate the possibility that the Jovian circumplanetary disk was populated with ice-depleted chondritic minerals, including phyllosilicates. We show that the dehydration of such particles and the outward diffusion of the released water vapor allow condensation of significant amounts of ice in the formation region of Ganymede and Callisto in the Jovian circumplanetary disk. Our model predicts that Europa, Ganymede, and Callisto should have accreted little, if any, volatiles other than water ice, in contrast to the comet-like composition of Saturn’s moon Enceladus. This mechanism allows for the presence of ice-rich moons in water-depleted formation environments around exoplanets as well.

Hourly Periodic Variations of Ultralow‐Frequency (ULF) Waves in Jupiter's Magnetosheath

AbstractPeriodic variations are widely identified in the Jovian system, varying from 10 s of seconds to several days or even longer. These processes are strongly influenced by solar wind conditions, planetary rotation and Io's volcanic activity. Ultralow‐frequency (ULF) waves at 10 s of minutes, which are the typical time scale of field‐line resonance, are considered as a crucial process in driving the Jovian energy circulation. The longer time‐scale periodicities are likely associated with global mass circulation. In this study, we focus on multihour variations of the ULF wave energy, which are difficult to identify within the magnetosphere due to the rapid planetary rotation modulation. Using the magnetic field observations from Juno and Galileo in Jupiter's magnetosheath, we found multiple significant multihour periodicities, widely distributed from 2 to 10 hr, peaked at different values from case to case. The most common periodicities were between 3 and 5 hr, existing in both the dawn and dusk sides. These common periodicities are likely associated with the energy transport from the inside to the magnetosheath.

The Dynamical Consequences of a Super-Earth in the Solar System

Placing the architecture of the solar system within the broader context of planetary architectures is one of the primary topics of interest within planetary science. Exoplanet discoveries have revealed a large range of system architectures, many of which differ substantially from the solar system’s model. One particular feature of exoplanet demographics is the relative prevalence of super-Earth planets, for which the solar system lacks a suitable analog, presenting a challenge to modeling their interiors and atmospheres. Here we present the results of a large suite of dynamical simulations that insert a hypothetical planet in the mass range 1–10 M ⊕ within the semimajor axis range 2–4 au, between the orbits of Mars and Jupiter. We show that, although the system dynamics remain largely unaffected when the additional planet is placed near 3 au, Mercury experiences substantial instability when the additional planet lies in the range 3.1–4.0 au, and perturbations to the Martian orbit primarily result when the additional planet lies in the range 2.0–2.7 au. We further show that, although Jupiter and Saturn experience relatively small orbital perturbations, the angular momentum transferred to the ice giants can result in their ejection from the system at key resonance locations of the additional planet. We discuss the implications of these results for the architecture of the inner and outer solar system planets, and for exoplanetary systems.

Electron impact ionization in the icy Galilean satellites’ atmospheres

Electron impact ionization is critical in producing the ionospheres on many planetary bodies and, as discussed here, is critical for interpreting spacecraft and telescopic observations of the tenuous atmospheres of the icy Galilean satellites of Jupiter (Europa, Ganymede, and Callisto), which form an interesting planetary system. Fortunately, laboratory measurements, extrapolated by theoretical models, were developed and published over a number of years by K. Becker and colleagues (see Deutsch et al. in Adv At Mol Opt Phys 57:87–155, 2009) to provide accurate electron impact ionization cross sections for atoms and molecules, which are crucial to correctly interpret these measurements. Because of their relevance for the Jovian icy satellites, we provide useful fits to the complex, semiempirical Deutsch–Märk formula for energy-dependent electron impact ionization cross sections of gas-phase water products (i.e., H $$_2$$ O, H $$_2$$ , O $$_2$$ , H, O). These are then used with measurements of the thermal plasma in the Jovian magnetosphere to produce ionization rates for comparison with solar photo-ionization rates at the icy Galilean satellites.

Nucleosynthetic isotope anomalies of zinc in meteorites constrain the origin of Earth's volatiles.

Material inherited from different nucleosynthesis sources imparts distinct isotopic signatures to meteorites and terrestrial planets. These nucleosynthetic isotope anomalies have been used to constrain the origins of material that formed Earth. However, anomalies have only been identified for elements with high condensation temperatures, leaving the origin of Earth's volatile elements unconstrained. We determined the isotope composition of the moderately volatile element zinc in 18 bulk meteorites and identified nucleosynthetic zinc isotope anomalies. Using a mass-balance model, we find that carbonaceous bodies, which likely formed beyond the orbit of Jupiter, delivered about half of Earth's zinc inventory. Combined with previous constraints obtained from studies of other elements, these results indicate that ~10% of Earth's mass was provided by carbonaceous material.

Microwaving Mimas, Enceladus, Tethys, Dione, Rhea, Iapetus and Phoebe: Insights into the regolith properties and geological history of Saturn's icy satellites

While Saturn's main airless moons are all composed largely of water ice, their respective thermal histories and near environments have led to different regolith compositions and structures. Part of this history is recorded in their subsurface which can be probed by microwaves. Using a combined thermal and radiative transfer model, we here investigate all distant observations acquired in the passive mode of the RADAR on board the Cassini spacecraft (2004–2017) at 2.2-cm wavelength. The joint analysis of the derived disk-integrated emissivities and published radar albedos provides new insights into the purity and maturity of the regolith of Saturn's icy moons. We find that satellite-to-satellite variations and large-scale regional anomalies in microwave signatures primarily reflect different degrees of contamination of the regolith by non-ice compounds. To a lesser extent, they may also point to different concentrations of scatterers in the subsurface; these scatterers must be made of ice and/or void rather than of non-ice contaminants. Enceladus appears to have the cleanest regolith likely due to the geological youth of its surface. Observations also suggest that the current heat flux emanating from this moon is not confined to the South Pole Terrain. In the inner system, the degree of purity of the satellites' regoliths decreases from Enceladus outward likely due to the decrease of the E-ring influx. In the outer system, Phoebe's ring mantles Iapetus' leading hemisphere with a decimetric layer of optically-dark and microwave-absorbent dust. Dione is surprisingly less radar-bright and more emissive than expected from both the observed general trend and the current understanding of its geological history. Another question remains outstanding: why are Saturnian moons, and to a lesser extent Jovian moons, so radar-bright at centimetric wavelengths? Current models assuming purely-random scattering in their subsurface fail to simultaneously reproduce active and passive microwave observations, especially for Saturn's inner moons. This may be due the presence of organized and especially efficient backscattering structures in their subsurface. The challenge is now to identify structures that are geologically plausible.

Size-selective accretion of dust on to CPDs: low CPD masses and filtration of larger grains

ABSTRACT The major satellites of Jupiter and Saturn are believed to have formed in circumplanetary discs (CPDs), which orbit forming giant protoplanets. Gas and dust in CPDs have different distributions and affect each other by drag, which varies with grain size. Yet simulations of multiple dust grain sizes with separate dynamics have not been done before. We seek to assess how much dust of each grain size there is in CPDs. We run multifluid 3D hydrodynamical simulations including gas and four discrete grain sizes of dust from 1 μm to 1 mm, representing a continuous distribution. We consider a 1MJup protoplanet embedded in a protoplanetary disc around a 1 M⊙ star. Our results show a truncated MRN (Mathis-Rumpl-Nordsieck) distribution at smaller grain sizes, which starts to tail off by a = 100 μm and is near zero at 1 mm. Large dust grains, which hold most of the dust mass, have very inefficient accretion to the CPD, due to dust filtration. Therefore, CPDs’ dust masses must be small, with mass ratio ∼ a few × 10−6 to the protoplanet. These masses and the corresponding millimetre opacities are in line with CPD fluxes observed to date.

Review of Trajectory Design and Optimization for Jovian System Exploration

Jupiter exploration is one of the focuses of deep space exploration in the near future. Design and optimization of trajectories in the Jovian system are crucial technologies for Jupiter exploration missions due to the unique and challenging multi-body dynamical environment. Various methodologies have been proposed and developed. However, there is a lack of comprehensive review of these methodologies, which is unfavorable for further developing new design techniques and proposing new mission schemes. This review provides a systematic summarization of the past and state-of-art methodologies for 4 main exploration phases, including Jupiter capture, the tour of the Galilean moons, Jupiter global mapping, and orbiting around and landing on a target moon. For each exploration phase, the related methods are categorized according to the fundamental features. The advantages and capabilities of the methods are described or analyzed, revealing the research progress. Finally, a prospect of future development of the methods is presented, aiming at providing references for further studies on trajectory design and optimization in the Jovian system.

A systematic mid-infrared spectroscopic study of thermally processed SO2 ices.

The use of mid-infrared spectroscopy to characterise the chemistry of icy interstellar and Solar System environments will be exploited in the near future to better understand the chemical processes and molecular inventories in various astronomical environments. This is, in part, due to observational work made possible by the recently launched James Webb Space Telescope as well as forthcoming missions to the outer Solar System that will observe in the mid-infrared spectroscopic region (e.g., the Jupiter Icy Moons Explorer and the Europa Clipper missions). However, such spectroscopic characterisations are crucially reliant upon the generation of laboratory data for comparative purposes. In this paper, we present an extensive mid-infrared characterisation of SO2 ice condensed at several cryogenic temperatures between 20 and 100 K and thermally annealed to sublimation in an ultrahigh-vacuum system. Our results are anticipated to be useful in confirming the detection (and possibly thermal history) of SO2 on various Solar System bodies, such as Ceres and the icy Galilean moons of Jupiter, as well as in interstellar icy grain mantles.

Unexpected long-term variability in Jupiter’s tropospheric temperatures

An essential component of planetary climatology is knowledge of the tropospheric temperature field and its variability. Previous studies of Jupiter hinted at periodic behavior that was non-seasonal, as well as dynamical relationships between tropospheric and stratospheric temperatures. However, these observations were made over time frames shorter than Jupiter's orbit or they used sparse sampling. We derived upper-tropospheric (300-mbar) temperatures over 40 years, extending those studies to cover several orbits of Jupiter, revealing unexpected results. Periodicities of 4, 7 8-9 and 10-14 years were discovered that involved different latitude bands and seem disconnected from seasonal changes in solar heating. Anti-correlations of variability in opposite hemispheres were particularly striking at 16, 22 and 30 degrees from the equator. Equatorial temperature variations are also anticorrelated with those 60-70 km above. Such behavior suggests a top-down control of equatorial tropospheric temperatures from stratospheric dynamics. Realistic future global climate models must address the origins of these variations in preparation for their extension to a wider array of gas-giant exoplanets.

Ice Transit and Performance Analysis for Cryorobotic Subglacial Access Missions on Earth and Europa.

Ice-covered ocean worlds, such as the Jovian moon Europa, are some of the prime targets for planetary exploration due to their high astrobiological potential. While upcoming space exploration missions, such as the Europa Clipper and JUICE missions, will give us further insight into the local cryoenvironment, any conclusive life detection investigation requires the capability to penetrate and transit the icy shell and access the subglacial ocean directly. Developing robust, autonomous cryorobotic technology for such a mission constitutes an extremely demanding multistakeholder challenge and requires a concentrated interdisciplinary effort between engineers, geoscientists, and astrobiologists. An important tool with which to foster cross-disciplinary work at an early stage of mission preparation is the virtual testbed. In this article, we report on recent progress in the development of an ice transit and performance model for later integration in such a virtual testbed. We introduce a trajectory model that, for the first time, allows for the evaluation of mission-critical parameters, such as transit time and average/overall power supply. Our workflow is applied to selected, existing cryobot designs while taking into consideration different terrestrial, as well as extraterrestrial, deployment scenarios. Specific analyses presented in this study show the tradeoff minimum transit time and maximum efficiency of a cryobot and allow for quantification of different sources of uncertainty to cryobot's trajectory models.

Tilting Uranus via the migration of an ancient satellite

Context. The 98° obliquity of Uranus is commonly attributed to giant impacts that occurred at the end of the planetary formation. This picture, however, is not devoid of weaknesses. Aims. On a billion-year timescale, the tidal migration of the satellites of Jupiter and Saturn has been shown to strongly affect their spin-axis dynamics. We aim to revisit the scenario of tilting Uranus in light of this mechanism. Methods. We analyse the precession spectrum of Uranus and identify the candidate secular spin-orbit resonances that could be responsible for the tilting. We determine the properties of the hypothetical ancient satellite required for a capture and explore the dynamics numerically. Results. If it migrates over 10 Uranus’s radii, a single satellite with minimum mass 4 × 10−4 Uranus’s mass is able to tilt Uranus from a small obliquity and make it converge towards 90°. In order to achieve the tilting in less than the age of the Solar System, the mean drift rate of the satellite must be comparable to the Moon’s current orbital expansion. Under these conditions, simulations show that Uranus is readily tilted over 80°. Beyond this point, the satellite is strongly destabilised and triggers a phase of chaotic motion for the planet’s spin axis. The chaotic phase ends when the satellite collides into the planet, ultimately freezing the planet’s obliquity in either a prograde or a plainly retrograde state (as Uranus today). Spin states resembling that of Uranus can be obtained with probabilities as large as 80%, but a bigger satellite is favoured, with mass 1.7 × 10−3 Uranus’s mass or more. Yet, a smaller ancient satellite is not categorically ruled out, and we discuss several ways to improve this basic scenario in future studies. Interactions among several pre-existing satellites are a promising possibility. Conclusions. The conditions required for the tilting seem broadly realistic, but it remains to be determined whether Uranus could have hosted a big primordial satellite subject to substantial tidal migration. The efficiency of tidal energy dissipation within Uranus is required to be much higher than traditionally assumed, more in line with that measured for the migration of Titan. Hints about these issues would be given by a measure of the expansion rate of Uranus’s main satellites.

Перспективы реализации наблюдательных программ ГАО РАН в обсерватории Ассы-Тургень

The progress of the observational programs of the Pulkovo observatory involves the transfer of some of them to regions with conducive astroclimatic conditions. The ability of the Assy-Turgen observatory (MPC = 217, h = 2700 m) operated by the Fesenkov Astrophysical Institute (AFIF), (Almaty, Republic of Kazakhstan) causes great interest in this context. The 40-cm telescope MEADE LX200 (Pulkovo Observatory) was transported to this site in 2022. In addition, it became possible to claim part of the observational time of the 1.5-meter AZT-20 telescope, which provides imaging both in the photometric mode in the griz bands and in the spectroscopic mode. The test observations were made with these instruments in August 2022. The present paper discusses the results of these observations and the prospects for further implementation of the Pulkovo observational programs at the Assy-Turgen observatory. It is shown that a positional accuracy better than 50 mas was reached with the 40-cm telescope measurements of the distant satellites of Jupiter and Saturn. Photometric measurements with this telescope allow us to obtain an accuracy of 0.02m. These are competitive values for many types of observations which will be significantly improved after the necessary deep alignment of the telescope optics. The astrometric accuracy of less than 20 mas is reachable with the AZT-20 telescope of this observatory (according to the internal convergence of astrometric measurements observations of the Uranian satellites). Spectral observations of the 61 Cygnus binary system were performed with this instrument in order to develop the method for determining the relative radial velocities. This is necessary to improve the accuracy of determining the orbital parameters of the binary star systems and searching for low-mass components and exoplanets.

Revisiting the Cassini States of synchronous satellites with an angular momentum approach

AbstractLike our Moon, the large icy satellites of Jupiter are thought to be in a Cassini State, an equilibrium rotation state characterized by a synchronous rotation rate and a precession rate of the rotation axis equal to that of the normal to the orbit. In these equilibrium states (up to four Cassini States are possible for a solid and rigid satellite), the spin axis of the satellite, the normal to its orbit and the normal to the inertial plane remain coplanar with an obliquity that remains theoretically constant. However, as the gravitational torque exerted on the satellite shows small periodic variations, the orientation of the rotation axis will also vary with time and nutations in obliquity will appear.Here we present a dynamical model for the study of the Cassini States. This model includes the coupling between the polar motion and the spin axis precession/nutation which is neglected in the classical studies. We study the influence of the triaxiality of Ganymede on its four possible Cassini States, use a Toy model of the Moon to illustrate the nutations in obliquity obtained with the dynamical model, and investigate the influence of the presence of a subsurface ocean on the Cassini State I of Europa.

Europa’s Plate Tectonic Activity Is Unlike Earth’s

The moon of Jupiter has likely experienced intermittent, regional plate tectonic activity in the past, although the plates are currently dormant.

Separation of quasi-continuous and periodic components of lineament formation at the Belus – Phoenix - Rhadamanthys Linea “triangle” on Europa

The first images of Jupiter's moon Europa from the Voyager missions sparked the curiosity about the lineament system appearing at the surface. Curiosity quickly turned into profound interest, following the discovery of its subsurface ocean, which may harbour life below the thick ice crust. This study revisits Europa and reinvestigates its surface using high-resolution Galileo data and mapping one of its most characteristic surface patterns: the complex network of lineaments. The analysis of the morphological type of over two hundred lineaments and their crosscutting relationship based on relative age indicate the influence of cyclical tidal force, orbital forcing, and the nonsynchronous rotation triggered periodic stress in the formation of three characteristic lineaments-generations, along with additional and unaccounted forces that may contribute to surface renewal. Despite ongoing debate, which suggests that Earth-like tectonism (e.g., subduction) is less likely plausible on Europa, the result of this study calls for some process acting along with tidal forces, causing shortening, horizontal movement and increasing extension in the ice plate located in the region of a suspected subduction (or low-relief subsumption) zone and may be part of the “subducting” crust. This study raises new questions and encourages additional scientific discussions, which, along with the Europa Clipper and JUICE missions, will help to understand the nature of Europa's ocean and ice-tectonic processes.

Dynamical history of the Galilean satellites for a fast migration of Callisto

Abstract The dynamics of the innermost Galilean satellites (Io, Europa, and Ganymede) is characterized by a chain of mean motion resonances, called Laplace resonance, and by a strong tidal dissipation that causes wide variations of their semimajor axes over large time-scales. The precise history of energy dissipation in the Jovian system is not known, but several theories have been proposed. Tidal resonance locking states that big outer moons can also migrate fast. If this is the case for Callisto, then it should have crossed the 2:1 mean motion resonance with Ganymede in the past, affecting the motion of all four Galilean satellites. Therefore, we aim to determine whether a fast migration for Callisto is compatible with the current orbital configuration of the system. Due to the chaotic nature of the resonant crossing, different outcomes are possible. A small portion of our simulations shows that Callisto can cross the 2:1 resonance with Ganymede without being captured and preserving the Laplace resonance. However, in most cases, we found that Callisto is captured into resonance, despite its divergent migration. As Callisto continues to migrate fast outwards, the moons depart substantially from the exact 8:4:2:1 commensurability, while still maintaining the resonant chain. Callisto can eventually escape it by crossing a high-order mean motion resonance with Ganymede. Afterwards, the moons’ system is able to relax to its current configuration for suitable dissipation parameters of the satellites. Therefore, it is possible, although challenging, to build a self-consistent picture of the past history of the Galilean satellites for a fast migration of Callisto.

Circumplanetary disk ices

Context. The large icy moons of Jupiter formed in a circumplanetary disk (CPD). CPDs are fed by vertically infalling circumstellar gas and dust which may be shock-heated upon accretion. Accreted material is then either incorporated into moons, falls into the planet, or is lost beyond the disk edge on relatively short timescales. If ices are sublimated during accretion onto the CPD we know there must be sufficient time for them to recondense or moons such as Ganymede or Callisto could not form. The chemical timescale to form sufficiently icy solids places a novel constraint on the dynamical behaviour and properties of CPDs.Aims. We aim to explore the process of ice formation in CPDs to constrain which disk properties (such as the mass, viscosity, and dust-to-gas ratio) are consistent with the formation of an icy moon system.Methods. We use the radiation thermochemical code ProDiMo(Protoplanetary Disk Model) to analyze how the radial ice abundance evolves in CPDs. We consider different initial chemical conditions of the disk to explore the consequences of infalling material being inherited from the circumstellar disk or being reset to atomic conditions by shock-heating. We contrast the timescales of ice formation with disk viscous timescales and radial dust drift.Results. We have derived the radial ice abundance and rate of ice formation in a small grid of model CPDs. Water ice can form very efficiently in the CPD from initially atomic conditions, as a significant fraction is efficiently re-deposited on dust grains within <1 yr. Radial grain drift timescales are in general longer than those of ice formation on grains. Icy grains of sizea <3 mm retain their icy mantles while crossing an optically thin circumstellar disk gap at 5 au forL*< 10L⊙.Conclusions. Three-body reactions play an important role in water formation in the dense midplane condition of CPDs. The CPD midplane must be depleted in dust relative to the circumstellar disk by a factor 10-50 to produce solids with the ice to rock ratio of the icy Galilean satellites. The CPD snowline is not erased by radial grain drift, which is consistent with the compositional gradient of the Galilean satellites being primordial.

Long-term changes in the Earth's climate: Milankovitch cycles as an exercise in classical mechanics

Long-term changes in the tilt of the Earth's axis, relative to the plane of its orbit, are of great significance to long-term climate change, because they control the size of the arctic and Antarctic circles. These “Milankovitch cycles” have hitherto been calculated by classical perturbation methods or by direct numerical integration of Newton's equations of motion. This paper presents an approximate calculation from simple considerations of angular momentum using similar methods to those used to study the precession of a spinning top. It is an instructive exercise in classical mechanics and gives a simple explanation of the phenomenon in terms of angular momentum. It is shown that the main component of “Milankovitch cycles” has a period of 41,000 yr and is due to one of the modes of precession of the Earth-Venus system. The other mode of this system produces a component of period 29,500 yr, and a third component of period 54,000 yr results from the influence of the precession of the orbits of Jupiter and Saturn. These results agree closely with several of the numerical simulations in the literature and strongly suggest that some other results in the literature are incorrect.

Absolute colors and phase coefficients of asteroids

Context. We use the phase curves of small bodies to measure absolute magnitudes and, together with complementary theoretical and laboratory results, to understand the micro- and macroscopic properties of their surfaces. Although we can observe asteroids up to phase angles of about 30 deg, the range of phase angles covered by outer Solar System objects usually does not go further than 7−10 deg for centaurs and 2 deg for trans-Neptunian objects, and a linear relation between magnitude and phase angle may be assumed. Aims. We aim to directly compare data taken for objects in the inner Solar System (inside the orbit of Jupiter) with data for centaurs and trans-Neptunian objects. Methods. We use the SLOAN Moving Objects Catalog (MOC) data to construct phase curves restricted to phase angles of less than or equal to 7.5 deg, which is compatible with the angles observed for the trans-Neptunian and Centaur population. We assume a linear model for the photometric behavior to obtain absolute magnitudes and phase coefficients in the ugirz, V, and R filters. Results. We obtain absolute magnitudes in seven filters for over 4000 objects. Our comparison with outer Solar System objects suggests the surfaces have a common property: intrinsically redder objects become blue with increasing phase angle, while the opposite happens for intrinsically bluer objects.