The Voyager 2 Photopolarimeter experiment has yielded the highest resolved data of Saturn's rings, exhibiting a wide variety of features. The B-ring region between 105000 km and 110000 km distance from Saturn has been investigated. It has a high matter density and contains no significance features visible by eye. Analysis with statistical methods has let us to the detection of two significant events. These features are correlated with the inner 3:2 resonances of the F-ring shepherd satellites Pandora and Prometheus, and may be evidence of large ring paricles caught in the corotation resonances.

The two Voyager spacecraft discovered small-scale, radially-extended features in the central region of Saturn's B Ring. These "spokes" are "clouds" of submicron-size ice grains which are electrostatically levitated above the ring plane and which appear to travel about Saturn in Keplerian orbits (Smith et al., 1981, Science 212, 163-191). This research project is a study of the dynamical and physical properties of spokes as deduced from Voyager Saturn ring images. An analysis of the orbital motion of two dynamically-anomalous spokes, in particular, has set limits on the charge-to-mass ratios of spoke particles at various times during their dynamical evolution. These two spokes have charge-to-mass ratios of at least -60 ± 3 C kg⁻¹ while corotating with Saturn, and charge-to-mass ratios of no more than -22 ± 2 C kg⁻¹ while orbiting Saturn at Keplerian velocities. Additionally, charge decay on the grains of these spokes, caused by solar UV photoemission, has allowed a lower limit of 0.10 ± 0.03 μm to be placed on the range of radii for spoke particles. In a study of spoke photometry, a single-scattering analysis of the 0.470-μm phase function for spokes has set a mean radius for the dominant scatterers (at this wavelength) of 0.22 ± 0.02 μm. Also, a multispectral analysis of spokes has determined the spectral index of the size distribution for spoke particles to be 2.1 ± 0.2. These dynamical and physical properties of spokes have been combined with theoretical explanations of spoke activity to develop a phenomenological model of spoke formation and evolution. The transport of angular momentum within the rings due to the radial motion of spoke grains is shown to be the most significant effect of spoke activity on the dynamical evolution of the B Ring, as was predicted by Goertz et al. (1986, Nature 320, 141-143). The radial mass transport velocity due to highly-charged spokes is -1 x 10⁻⁹ m s⁻¹. The subsequent spreading time for the B Ring is 600 million years, which is significantly less than the 4.6 billion-year age of the solar system.

As our abilities to utilise high performance computing to theoretically probe many astrophysical systems increases, a genuine need to relate to real systems becomes ever more important. Here, Saturn s rings can be used as a nearby laboratory to investigate in real time many astrophysical processes. One such system is the narrow F ring and its interaction with its inner shepherd moon Prometheus. Through numerical modelling and direct observations of the in-situ spacecraft Cassini we find new and exciting dynamics. These might help explain some of the asymmetries witnessed in the distribution of embedded moonlets and azimuthal ring brightness known to exist within the F ring. Spatially we find asymmetry in the Prometheus induced channel edges with regards to density, velocity and acceleration variations of ring particles. Channel edges that show fans (embedded moonlets) are also the locations of highly localised increases in densities, velocity and acceleration changes where opposing edges are considerably less localised in their distribution. As a result of the highly localised nature of the velocity and acceleration changes chaotic fluctuations in density were witnessed. However, this could seek to work in favour of creating coherent objects at this channel edge as density increases were significantly large. Thus, density here had a greater chance of being enhanced beyond the local Roche density. Accompanied with these dynamics was the discovery of a non-zero component to vorticity in the perturbed area of the F ring post encounter. By removal of the background Keplerian flow we find that encounters typically created a large scale rotation of ~10,000 km^2. Within this area a much more rich distribution of local rotations is also seen located in and around the channel edges. Although the real F ring and our models are non-hydrodynamical in nature the existence of a curl in the velocity vector field in the perturbed region could offer some interesting implications for those systems that are gas rich.

Orientadores: Maximiliano Ujevic Tonino, Javier Fernando Ramos Caro, Carola Dobrigkeit Chinellato / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Física Gleb Wataghin / Made available in DSpace on 2018-08-20T00:26:31Z (GMT). No. of bitstreams: 1 AlarconLLacctarimay_CesarJuan_D.pdf: 2806949 bytes, checksum: 588125c56d514dbfd77030a564888461 (MD5) Previous issue date: 2012 / Resumo: Nesta tese pretendemos modelar a distribuição de matéria em um Anel estelar fino imerso no campo gravitacional de um e dois Satélites Shepherds (Satélites Pastores) usando a equação de Fokker-Planck. Em particular, estudamos a evolução de um anel fino ao redor de um monopolo central. Os coeficientes de difusão são aqui calculados e escritos em termos de um ¿potencial¿ semelhante aos usuais potencias de Rosenbluth. Neste caso, consideramos que as partículas campo obedecem uma distribuição Gaussiana. Resolvemos a equação de Fokker-Planck 1-dimensional para a função de distribuição das partículas teste que conformam o anel usando o método das diferenças finitas (versão Euler implícita). Demonstramos que o anel é uma configuração estável para uma evolução de longo tempo, tanto na ausência como na presença de shepherds. Estudamos também a variação da densidade de massa do anel para diferentes configurações. Em todos os casos é observada uma variação máxima e negativa da densidade perto da localização do shepherd devido a efeitos dinâmicos / Abstract: In this thesis we intend to model the distribution of matter in a thin stellar ring immersed in the gravitational field of one and two shepherd satellites using the Fokker-Planck equation. In particular, we study the evolution of a thin ring around a central monopole. The diffusion coefficients are calculated and written in terms of a ¿potential¿ similar to the usual Rosenbluth potentials. In this case, we consider that the particles follow a Gaussian distribution. We solve the 1-dimensional Fokker-Planck equation for the ring particles distribution function using the finite difference method (implicit Euler version). We show that the ring is a stable configuration for long time evolutions in the absence or in the presence of shepherds. We also studied the change in the mass density of the ring for different configurations. In all of the cases, it is observed a maximum negative variation of the density near the location of the shepherd due to dynamical effects / Doutorado / Física / Doutor em Ciências

Orientador: Rafael Sfair / Resumo: O estudo dos anéis planetários pode ser usado como laboratório para a compreensão do processo de formação e dinâmica planetária. Anéis planetários são formados por partículas pequenas que sofrem a ação de diversas forças, além da força gravitacional. O estudo da dinâmica dos anéis pode ser abordado através de simulações numéricas para o problema de N-corpos. Neste trabalho apresentamos a adaptação do pacote REBOUND (Rein & Liu, 2012) através da inclusão de forças perturbativas para estudar a dinâmica de anéis planetários. Uma fonte de perturbação de origem gravitacional é devida ao formato não esférico do planeta, que pode ser representado com precisão até a expansão do potencial do termo J6. Além dessa, as principais são a força eletromagnética e a pressão de radiação solar. Também atuam forças de arrasto, como o de Poynting-Robertson e, eventualmente, as forças devido a atmosfera e do plasma. Embora sejam mais fracas, essas forças alteram a energia orbital das partículas e dominam a dinâmica em longos períodos de tempo. Abordamos essas forças através do REBOUND e verificamos os principais efeitos de cada uma das forças, cuja força devido ao formato não esférico do planeta causa uma precessão na longitude do pericentro, enquanto a força eletromagnética causa uma regressão e que ambas combinadas contribuem uma com a outra alterando a taxa de variação da longitude do pericentro. Já a força da pressão de radiação altera o formato da órbita e as forças de arrasto diminuem o semi... (Resumo completo, clicar acesso eletrônico abaixo) / Mestre

<div>Planetary rings are, and have been, a common feature throughout the solar system.</div><div>Rings have been observed orbiting each of the giant planets, several Trans-Neptunian Objects, and debris rings are thought to have orbited both Earth and Mars.</div><div>The bright, massive planetary rings orbiting Saturn have been observed for centuries, and the Cassini Mission has given researchers a recent and extensive closeup view of these rings.</div><div>The Saturn ring system has served as a natural laboratory for scientists to understand the dynamics of planetary ring systems, as well as their influence on satellites orbiting nearby.</div><div>Researchers have shown that planetary ring systems and nearby satellites can be tightly-coupled systems.</div><div><br></div><div>In this work, I discuss the physics which dominate the dynamical evolution of planetary ring systems, as well as the interactions with any nearby satellites.</div><div>Many of these dynamics have been incorporated into a one-dimensional mixed Eulerian-Lagrangian numerical model that I call "RING-MOONS," to simulate the long-term evolution of tightly coupled satellite-ring systems.</div><div>In developing RING-MOONS, I have discovered that there are three evolution regimes for tightly-coupled satellite-ring systems which I designate as the "Boomerang," "Torque-Dependent," and "Slingshot" regimes.</div><div>Each regime may be defined using the rotation period of the primary body and the bulk density of the ring material.</div><div><br></div><div>The slow rotation period of Mars places it in the Boomerang regime.</div><div>I hypothesize that a giant impact with Mars ejected material into orbit, forming a debris ring around the planet.</div><div>Using RING-MOONS, I demonstrate how Lindblad torques cause satellites which form at the edge of the ring to initially migrate away from the ring, but over time as the mass of the ring decreases, tidal torques always cause the satellites to migrate inwards.</div><div>Assuming the satellites rapidly tidally disrupt upon migrating to the rigid Roche limit, a new ring is formed.</div><div>I show that debris material cycles between orbiting Mars as a planetary ring, or as discrete satellites, and that Phobos may be a product of a repeated satellite-ring cycle.</div><div>Uranus, which has a faster rotation rate falls within the Torque-Dependent regime.</div><div>Hypothesizing that a massive ring once orbited Uranus, I use RING-MOONS to demonstrate how the satellite Miranda may have formed from such a ring, and migrated outwards to its current orbit, but that any other satellites would have migrated inwards overtime.</div><div><br></div><div>Lastly, I examine Trans-Neptunian Objects (TNOs) in binary systems.</div><div>Tidal torques exerted on each body can decrease the mutual semi-major axis of the system.</div><div>I outline the conditions for which a fully synchronous system may experience a complete decay of the mutual orbit due to tidal torques.</div><div>As the semi-major axis decreases, it is possible for the smaller of the two bodies to shed mass before coming into contact with the more massive to form a contact binary.</div><div>I hypothesize that Chariklo and Chiron are contact binaries that formed via the tidal collapse of a binary TNOs system, and demonstrate how mass shedding may have occurred to form the rings observed today.</div>

Orientador: Silvia Maria Giuliatti Winter / Resumo: Orbitando Saturno encontram-se Anthe, Methone e Aegaeon, três pequenos satélites coorbitais a arcos planetários e em ressonância de corrotação excêntrica com o satélite Mimas, do tipo 10:11 para o arco de Anthe, 14:15 para o arco de Methone e do tipo 7:6 para o arco do anel G (arco coorbital ao satélite Aegaeon). Neste trabalho é estudada a dinâmica de partículas micrométricas em ressonância de corrotação excêntrica, sob o efeito de forças perturbadoras (força de radiação solar e arrasto do plasma) e da influência gravitacional de pequenos satélites. A ressonância de corrotação excêntrica m + 1:m é responsável por criar m sítios nos quais as partículas permanecem azimutalmente confinadas. Quando incluídos satélites hipotéticos nos sítios, as partículas rapidamente colidem como estes, de modo que os sítios ficam vazios em algumas centenas de anos. Ainda foi constatado que existe uma correlação entre o tempo de vida das partículas com o tamanho físico do satélite, sendo verificado um aumento do tempo de vida dos sítios com o raio do satélite, para satélites com raios da ordem de metros, passando a decrescer para satélites com raios da ordem de quilômetros. Tal resultado se deve ao fato dos satélites pequenos tenderem a apenas perturbar a órbita das partículas, as quais realizam maiores excursões em relação ao centro do sítio, enquanto satélites maiores confinam as partículas azimutalmente, de modo que estas permanecem em ressonância de corrotação com Mimas e com o satélite. Efe... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: Anthe, Methone and Aegaeon are three tiny saturnian moons. They are coorbital to planetary arcs and are trapped in corotation eccentric resonances with Mimas: 10:11 Anthe’s arc, 14:15 Methone’s arc and 7:6 G ring arc (Aegaeon’s arc). In this work we studied the dynamics of the particles trapped in the corotation eccentric resonances under the effects of dissipative forces (solar radiation force and plasma drag) and coorbitals moonlets. The m + 1:m corotation eccentric resonance creates m sites where the particles will be azimuthally confined for more than 100 thousand years. When satellites are located in the sites, the particles quickly collide with them and these sites are cleaned in a few hundred years. We verified an increase in the lifetime of the sites with the satellites’ radii, for moons with radius of the order of meters, and a decrease in the lifetime with an increase of the satellites’ radii, for kilometer-sized satellites. Satellites with radii of the order of meters only disturb the particles’ orbits, so the particles perform large excursions in relation to the site’s center. Satellites with kilometric radii azimuthally confine the particles, wich remain in resonance with Mimas and with the coorbital satellite. The solar radiation force and plasma drag effects on the semimajor axis remove particles from the azimuthal confinement and the effects on the eccentricity favor collisions with the satellites. The sites of the 7:6, 14:15 and 10:11 corotation resonance, if... (Complete abstract click electronic access below) / Mestre

Since their discovery in 1610 by Galileo Galilei, Saturn's rings continue to fascinate both experts and amateurs. Countless numbers of icy grains in almost Keplerian orbits reveal a wealth of structures such as ringlets, voids and gaps, wakes and waves, and many more. Grains are found to increase in size with increasing radial distance to Saturn. Recently discovered "propeller" structures in the Cassini spacecraft data, provide evidence for the existence of embedded moonlets. In the wake of these findings, the discussion resumes about origin and evolution of planetary rings, and growth processes in tidal environments. In this thesis, a contact model for binary adhesive, viscoelastic collisions is developed that accounts for agglomeration as well as restitution. Collisional outcomes are crucially determined by the impact speed and masses of the collision partners and yield a maximal impact velocity at which agglomeration still occurs. Based on the latter, a self-consistent kinetic concept is proposed. The model considers all possible collisional outcomes as there are coagulation, restitution, and fragmentation. Emphasizing the evolution of the mass spectrum and furthermore concentrating on coagulation alone, a coagulation equation, including a restricted sticking probability is derived. The otherwise phenomenological Smoluchowski equation is reproduced from basic principles and denotes a limit case to the derived coagulation equation. Qualitative and quantitative analysis of the relevance of adhesion to force-free granular gases and to those under the influence of Keplerian shear is investigated. Capture probability, agglomerate stability, and the mass spectrum evolution are investigated in the context of adhesive interactions. A size dependent radial limit distance from the central planet is obtained refining the Roche criterion. Furthermore, capture probability in the presence of adhesion is generally different compared to the case of pure gravitational capture. In contrast to a Smoluchowski-type evolution of the mass spectrum, numerical simulations of the obtained coagulation equation revealed, that a transition from smaller grains to larger bodies cannot occur via a collisional cascade alone. For parameters used in this study, effective growth ceases at an average size of centimeters. / Seit ihrer Entdeckung im Jahre 1610 durch Galileo Galilei faszinieren die Ringe des Saturn sowohl Laien als auch Experten. Planetare Ringe finden sich in der Äquatorialebene aller vier Riesenplaneten unseres Sonnensystems und sind eines der eindruckvollsten Beispiele granularer Gase. Darunter gehören die Saturnringe zu den Bekanntesten. Sie bergen eine Vielzahl von Strukturen und erstrecken sich über mehr als 240 000 Kilometer, wobei sie weit weniger als 100 Meter dick sind. Unzählige kleinerer Körper bewegen sich auf leicht exzentrischen Kepler-ähnlichen Bahnen um den Zentralplaneten und bestehen dabei vorwiegend aus Eis. Die seit Juli 2004 im Orbit um den Saturn befindliche Raumsonde Cassini liefert atemberaubende Bilder und Daten, die nicht nur neue Erkenntnisse liefern, sondern auch alte Fragestellungen neu aufleben lassen. Dazu gehört z.B. die Frage nach dem Ursprung und den Entwicklungsstufen planetarer Ringe. Kürzlich, im äusseren A-Ring entdeckte Kleinmonde, deren Existenz schon viel früher postuliert wurde, weisen auf eventuell stattfindende Wachstumsprozesse hin. Da sich planetare Ringe jedoch hauptsächlich innerhalb der sogenannten Roche-Zone des jeweiligen Planeten befinden, ist ein effektives, allein auf gravitativen Wechselwirkungen beruhendes Größenwachstum nicht zu erwarten. Der Einfluß von Teilchenadhäsion auf diese Prozesse ist bis dato fraglich. Im Rahmen dieser Dissertation ist ein Kontaktmodell für adhäsive, viskoelastische Binärstöße granularer Teilchen entwickelt worden, welches sowohl deren Agglomeration als auch Restitution gestattet. Chakateristisch für granulare Materie ist die dissipative Wechselwirkung der einzelnen Teilchen untereinander. Dieser Energieverlust wird gewöhnlich mittels des Restitutionskoeffizienten erfaßt, der das Verhältnis von Relativgeschwindigkeiten nach zu vor dem Stoß darstellt. Dieser Parameter ermöglicht es, Agglomeration und Restitution nicht nur qualitativ sondern auch quantitativ voneinander zu unterscheiden. Ferner ergibt sich eine maximale Impaktgeschwindigkeit, bei der eine Agglomeration noch immer möglich ist. Basierend auf der Existenz derartiger Grenzgeschwindigkeiten für Agglomeration und Fragmentation, wurde in dieser Dissertation ein selbstkonsistentes, kinetisches Strukturbildungsmodell vorgestellt und im Hinblick auf die Koagulation von Teilchen weitergehend untersucht. Eine Koagulationsgleichung, die einer eingeschränkten Haftwahrscheinlichkeit Rechnung trägt, ist analytisch hergeleitet worden. Aus ihr läßt sich die allgemein bekannte, aber ansonsten phenomenologische Smoluchowski Gleichung als ein Grenzfall ableiten, bei dem jeder mögliche Kontakt zur Koagulation führt. Qualitative und quantitative Untersuchungen der Relevanz von Adhäsion in kräftefreien und Kepler-gescherten Systemen beziehen sich auf die Stabilität von Zwei-Teilchen-Agglomeraten, die Wahrscheinlichkeit eines gegenseitigen "Einfangens" beider Teilchen, und die zeitliche Entwicklung der Größenverteilung unter Berücksichtigung der im ersten Teil dieser Arbeit eingeführten Kollisionsdynamik. Dabei ergab sich ein kritischer Abstand zum Zentralkörper, der das ansonsten in diesem Rahmen benutzte Roche Kriterium erweitert. Numerische Simulationen der vorgestellten Koagulationsgleichung zeigen deutlich, daß im Vergleich zu Smoluchowski-ähnlichem Verhalten, ein kollisionsbasiertes Wachstum von kleineren zu größeren Körpern nicht notwendigerweise auftritt. Lediglich Größen von Zentimetern konnten an dieser Stelle erreicht werden. Die Relevanz von adhäsiven Teilchenwechselwirkungen konnte damit nachgewiesen werden. Vermögen diese auch nicht für ein effektives Wachstum aufzukommen, so sind sie dennoch von Bedeutung für die kollektive Dynamik planetarer Ringe.