Planetary Ring Systems Research Articles

Inertial Alfvén waves with polarization force in a dusty plasma

The properties of dust inertial Alfvén waves (DIAWs) in a dusty plasma with the effects of polarization force are investigated. First, the dispersion equation is obtained from the fluid equations by considering the polarization force. Then, the energy balance equation is deduced by applying the Sagdeev pseudopotential method. It is shown that the polarization force affects the characteristics of DIAWs as well as the pseudopotential significantly. In addition, the existence of the polarization force changes the width of DIAWs. The present results may be helpful in further understanding the effect of polarization forces on the formation of linear and nonlinear structures of Alfvén waves in the laboratory plasma, astrophysical dusty plasma systems, planetary ring systems, cometary tails, etc.

Unusual one-armed density waves in the Cassini Division of Saturn's rings

We identify several unusual one-armed density waves in Saturn's Cassini Division, using occultation observations from the Cassini RSS and VIMS instruments. In the inner Cassini Division, we identify outward-propagating density waves with wavenumber m = 1 located near 118,050 km (W118.05), 118,400 km (W118.40), and 118,530 km (W118.53). From Cassini ISS images taken at very low incidence angles we find evidence for vertical structure in these waves, which may be evidence for splashing of ring material in the crests of the waves. We propose that these waves are driven by nearby eccentric ringlets, probably the Strange (or R6) and Herschel ringlets. In the outer Cassini Division, we identify a wave structure near 120,200 km (W120.20), between the Laplace and Bessel gaps, as a conspicuous example of a standing wave in a planetary ring system. It appears to be the superposition of an outward-propagating m = 1 density wave, probably driven by the nearby Laplace ringlet, and its reflection at the inner edge of the Bessel gap.

Chime’s Laws for Distribution of Planets, Moons and Planetary Ring-Systems: Critical Examination of Their Predictions and the Implications

Study Aim: The problem as to whether planets, moons and planetary ring-systems are randomly or non-randomly distributed in the solar system has not been resolved. In this article, the predictions of Chime’s laws for distribution of bodies were critically examined in order to see if planets, moons and planetary ring-systems were randomly or non-randomly distributed in the solar system. Method: Equations formulated based on the distribution of the known planets, moons and planetary ring-systems in the solar system, were used to predict the distribution of these bodies in all the planetary orbits of the solar system. The predictions made by those equations were then compared with observations. Result: The solar system is a 14-orbit system which has between 9 and 13 formed planets, between 190 and 248 formed moons and 6 planetary ring-systems. Many Jupiter’s moons are missing. About three Uranus’ moons await discovery. Pluto is Planet 10 which was predicted to have 6 moons and a planetary ring-system. Planet Eleven, predicted to have 2 moons and a planetary ring-system, has not yet been discovered. The non-random distribution of planets, moons and planetary ring-systems in the solar system favoured a formation process that was not prone to chance. There are serious flaws in the IAU definition of planet, which was why it was unable to recognize that Pluto is a Planet. Conclusion: This study has shown that planets, moons and planetary ring-systems are non-randomly distributed in the solar system. The simplicity, elegance and Fibonacci-friendliness of the <i>beta total orbital bodies distribution laws</i> make them very attractive. No standard ring-system or any more moons are expected to be discovered in Section 2.1.1 of the solar system. Astronomers should, therefore, channel their energies and limited resources towards Section 2.1.2 of the solar system where it is necessary to resolve such puzzles as the number of Jupiter’s moons that are actually missing, the group of laws that is operative in the solar system and the fate of <i>Warsawlene</i>, the sixth moon of Pluto. There are serious flaws in the 2006 IAU definition of planet. Systematic theoretical explorations of Division 2.2 should commence with Orbit Eleven and its planet. Recommendations: Search for the three undiscovered moons of Uranus labeled <i>Ezechi, Akanene</i> and <i>Ikechukwu</i> in the order in which they will be discovered; search for the sixth moon of Pluto, <i>Warsawlene</i>; recognizing the planetary status of Pluto; serious efforts to discover Planet Eleven; and coming up with a new and better definition of planet.

Evidence for Quantisation in Planetary Ring Systems

Evidence for Quantisation in Planetary Ring Systems

Rings of a Super Saturn.

The article focuses on research on rings discovered larger than that of Saturn planet. Topics discussed include discovery of a gargantuan planetary ring system by astronomers that is some 200 times larger than Saturn ring, collaboration of professional and amateur astronomers to study the system in detail and models suggesting that rings harbor a Mars-sized moon.

Kinetic effects of the dust charge fluctuations on the instability of dust ion-acoustic waves

In this paper, a kinetic description is used to derive the perturbed dust grain currents carried by the plasma particles, taking into account dust charge fluctuations. The longitudinal dielectric permittivity and the dispersion relation of dust ion-acoustic waves in an unmagnetized dusty plasma are obtained. It is shown that the dust charge fluctuations effectively modify the damping rate of these waves, which can lead to an excitation of instability in plasma. This instability is due to the thermal velocity of the plasma particles and dust charge fluctuations. It is different from the instability due to the drift speed of the plasma particles. It is found that there is a critical wave number above which these waves are unstable. In addition, the growth rate of these waves is numerically investigated for different plasma parameters. The present theory is applicable in astronomers and space scientists working on dusty plasmas, especially planetary ring systems and cometary tails, where dust charge fluctuations are important.

Collisions of small ice particles under microgravity conditions

Context: Understanding the collisional properties of ice is important for understanding both the early stages of planet formation and the evolution of planetary ring systems. Simple chemicals such as methanol and formic acid are known to be present in cold protostellar regions alongside the dominant water ice; they are also likely to be incorporated into planets which form in protoplanetary disks, and planetary ring systems. However, the effect of the chemical composition of the ice on its collisional properties has not yet been studied. Aims: Collisions of 1.5 cm ice spheres composed of pure crystalline water ice, water with 5% methanol, and water with 5% formic acid were investigated to determine the effect of the ice composition on the collisional outcomes. Methods: The collisions were conducted in a dedicated experimental instrument, operated under microgravity conditions, at relative particle impact velocities between 0.01 and 0.19 m s^-1, temperatures between 131 and 160 K and a pressure of around 10^-5 mbar. Results: A range of coefficients of restitution were found, with no correlation between this and the chemical composition, relative impact velocity, or temperature. Conclusions: We conclude that the chemical composition of the ice (at the level of 95% water ice and 5% methanol or formic acid) does not affect the collisional properties at these temperatures and pressures due to the inability of surface wetting to take place. At a level of 5% methanol or formic acid, the structure is likely to be dominated by crystalline water ice, leading to no change in collisional properties. The surface roughness of the particles is the dominant factor in explaining the range of coefficients of restitution.

A stochastic Burgers-Zeldovich model for the formation of planetary ring systems and the satellites of Jupiter and Saturn

We consider a proto-ring nebula of a gas giant such as Neptune as a cloud of gas/dust particles whose behaviour is governed by the stochastic mechanics associated to the Kepler problem. This leads to a stochastic Burgers-Zeldovich type model for the formation of planetesimals involving a stochastic Burgers equation with vorticity which could help to explain the turbulent behaviour observed in ring systems. The Burgers fluid density and the distribution of the mass M(T) of a spherical planetesimal of radius δ are computed for times T. For circular orbits, sufficient conditions on certain time averages of δ2 are given ensuring that VarM(T) ∼ 0 as T ∼ ∞. Some applications are given to the satellites of Jupiter and Saturn, in particular giving a possible explanation of the equal mass families of satellites.

On the Edgeworth‐Kuiper Belt dust flux to Saturn

Dust grains originating from the Edgeworth‐Kuiper Belt (EKB) are believed to be the dominant species of dust in the outer solar system. These grains, evolving inward from the EKB under the influence of a variety of forces, will encounter the giant planets or their ring and moon systems. At Saturn, this influx drives several physical processes including the generation of tenuous dusty exospheres and rings, the spatial and compositional evolution of Saturn's main planetary ring system, and the generation of ionospheric and neutral gas layers in the atmospheres of Saturn and Titan. Recent comparisons between in‐situ dust density measurements in the outer solar system and a dynamical dust grain tracing model have placed experimental limits on the mass production rate and power‐law exponent of EKB‐generated grains. Using this model and the experimental constraints, we make predictions for the influx of micron‐sized, EKB‐generated grains into the saturnian system, where the Cosmic Dust Analyzer onboard the Cassini mission is currently making measurements of both endogenous and exogenous dust populations.

Nonlinear Evolution of the Dust Acoustic Instability in Artificially Created Dusty Space Plasmas

A 2-D hybrid electrostatic model is used to investigate the dust acoustic instability driven by an ion beam. To understand the generation and the nonlinear electrostatic waves, we investigate possible parameter regimes for the dust acoustic instability. The principal application involves the Charged Aerosol Release Experiment in the ionosphere, but also potential applications are for the planetary ring system of Saturn. The plasma background ions and charged dust are treated as discrete particles, whereas electrons are dealt with as a Boltzmann fluid. A Monte Carlo collision model is adopted to deal with the ion-neutral collisions. The kinetic dispersion relation is numerically solved to investigate effects of the ion drift velocity and the dust charge and density on the wave growth rate and the wave propagation direction. The simulation results agree with linear analysis of the instability, which also shows that the most unstable dust acoustic wave may obliquely propagate to the streaming direction. This may be important for radar diagnostics. The wave saturates by trapping dust. The waves damp out as the ion-neutral collision frequency increases comparable with the wave growth rate, and more importantly, such collision may lead to unstable waves propagating even further off the streaming direction.

Constraints on dust production in the Edgeworth-Kuiper Belt from Pioneer 10 and New Horizons measurements

[1] Impact ejecta and collisional debris from the Edgeworth-Kuiper Belt are the dominant source of micron-sized grains in the outer solar system, as they slowly migrate inwards through the outer solar system before most grains are ejected during close encounters with Jupiter. These grains drive several phenomena in the outer solar system, including the generation of impact ejecta clouds at airless bodies, the formation of ionospheric layers and neutral gases in the atmospheres of the giant planets due to meteoric ablation, the generation of tenuous outer planetary ring systems and the spatial and compositional alteration of Saturn's main rings. Previous analyses have offered estimates of the net mass production rate from the Edgeworth-Kuiper Belt both theoretically and observationally. In order to improve upon these estimates, we compare measurements of the interplanetary dust density in the outer solar system by both the Pioneer 10 meteoroid detector and the New Horizons Student Dust Counter with a dynamical dust grain tracing model. Our best estimates for the net mass production rate and the ejecta mass distribution power law exponent are (8.9 ± 0.5) × 105 g/s and 3.02 ± 0.04, respectively.

Dust ion-acoustic solitary and shock waves due to dust charge fluctuation with vortexlike electrons

A rigorous theoretical investigation has been made of the dust ion-acoustic (DIA) solitary and shock waves in an unmagnetized dusty plasma (containing vortexlike electrons, mobile ions, and charge fluctuating static dust) by reductive perturbation method. The effects of dust grain charge fluctuation and vortexlike (trapped) electron are found to modify the properties of the DIA solitary and shock waves significantly. The implications of these results for some space and astrophysical dusty plasma systems, especially planetary ring systems, are briefly mentioned.

The Jovian Rings

AbstractA comparison of the Jovian and Saturnian rings is made by reviewing the recent advances in planetary spacecraft exploration and theoretical study. Two main issues are addressed, namely, the different structures of these two planetary ring systems and the water ice composition of the Saturnian rings. It is suggested that answers might be found by invoking tidal capture of Trans-Neptunian Objects with highly differentiated structures even though catastrophic breakup of pre-existing satellites in the ring regions remains a real possibility. Erosion mechanisms such as meteoroid impact, photo-sputtering, orbital instability of charged dust particles and thermal evaporation acting at different time scales could lead to the preservation of the Saturnian ring system but not the Jovian ring system of large mass originally.

Planetary ring systems

Planetary ring systems

How Prometheus creates structure in Saturn's F ring

Images of Saturn's narrow and contorted F ring returned by the Cassini spacecraft have revealed phenomena not previously detected in any planetary ring system. The perturbing effect of the inner shepherding satellite, Prometheus, seems to introduce channels through the F ring and a 'streamer'--a line of particles that link the ring to the satellite. The detailed mechanism for the formation of these features has been lacking an explanation. Here we show that these phenomena can be understood in terms of a simple gravitational interaction as Prometheus approaches and recedes from the F ring every 14.7 hours. Our numerical models show that as Prometheus recedes from its closest approach to the F ring, it draws out ring material; one orbital period later, this affected region has undergone keplerian shear and is visible as a channel, in excellent agreement with structures seen in the Cassini images. Prometheus' periodic disruption of the F ring will become more pronounced as the two orbits approach their minimum separation in 2009. The model predicts that the appearance of streamers and the associated channels will vary in a regular fashion on a timescale of one orbital period.

Low-frequency electrostatic dust-modes in a non-uniform magnetized dusty plasma

A self-consistent and general description of obliquely propagating low-frequency electrostatic dust-modes in a non-uniform magnetized dusty plasma system has been presented. A number of different situations, which correspond to different low-frequency electrostatic dust-modes, namely, dust-acoustic mode, dust-drift mode, dust-cyclotron mode, dust-lower-hybrid mode, and other associated modes (such as, accelerated and retarded dust-acoustic modes, accelerated and retarded dust-lower-hybrid modes, etc.), have also been investigated. It has been shown that the effects of obliqueness and inhomogeneities in plasma particle number densities introduce new electrostatic dust modes as well as significantly modify the dispersion properties of the other low-frequency electrostatic dust associated modes. The implications of these results to some space and astrophysical dusty plasma systems, especially to planetary ring-systems and cometary tails, are briefly mentioned.

Nonlinear electromagnetic modes in astrophysical plasmas with dust distributions

A derivative nonlinear Schrodinger equation is obtained for parallel electromagnetic modes in plasmas containing polydisperse charged dust. The coefficient of the dispersive term in that equation is dominated by the dust rather than the (plasma) ions, and polydisperse dust yields a larger coefficient in absolute value than an equivalent monodisperse description. This leads to a significant broadening of the nonlinear structure due to the presence of polydisperse rather than monodisperse dust, the latter contributing in itself already to a substantial increase in the width of envelope solitons compared to dust-free plasmas. When modelling the charged dust by a power-law distribution occurring in planetary ring and other astrophysical systems, it depends very much on the power-law index whether the smaller or the larger grains are more important. For certain indices the more numerous smaller grains determine the charge and mass densities, but the larger dust dominates the linear and nonlinear dispersive effects.

Dust-cyclotron and dust-lower-hybrid modes in self-gravitating magnetized dusty plasmas

Theoretical investigation has been made on two different ultra-low-frequency electrostatic modes, namely, dust-cyclotron mode and dust-lower-hybrid mode, propagating perpendicular to the external magnetic field, in a self-gravitating magnetized two-fluid dusty plasma system. It has been shown that the effect of the self-gravitational force, acting on both dust grains and ions, significantly modifies the dispersion properties of these two electrostatic modes. The implications of these results to some space and astrophysical dusty plasma systems, especially to planetary ring-systems and cometary tails, are briefly mentioned.

Saturn Ring Observer

Scientists studying planetary ring systems and planetary system formation have long wanted close-up (a few km) observations of Saturn's rings to answer fundamental questions about ring particle characteristics and behavior. But missions to implement these observations involve post-approach Δ V requirements greater than 10 km/ s , so past designs have called upon Nuclear Electric Propulsion—an untenable position in the current programmatic climate. A unique new mission design uses carefully designed aerocapture to decrease the Δ V requirement to as little as 3.5 km/ s , a difficult but not impossible feat for high-performance chemical propulsion systems. Propulsion costs dominate cost estimates for the Saturn Ring Observer mission. Driving down propulsion costs is an important facet of the strategic technology program, one that would provide cost benefits to many other missions.

Nonlinear electrostatic waves in a magnetized dust-ion plasma

It is shown that the nonlinear equation governing the dynamics of coupled dust-acoustic and dust-cyclotron waves in a magnetized dust-ion plasma can be written in the form of an energy integral. The latter is analyzed analytically as well as numerically to investigate the properties of arbitrary amplitude solitary waves. It is found both analytically as well as numerically that there exist solitary waves only with a negative potential. The implications of these results to some space and astrophysical dusty plasma systems, especially to planetary ring systems and cometary tails, are briefly discussed.