Academic literature on the topic 'Planetary arcs'

Orientador: Silvia Maria Giuliatti Winter<br>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)<br>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)<br>Mestre

Orientador: Rafael Sfair de Oliveira<br>Resumo: A formação de alguns arcos dos anéis planetários pode estar relacionada às colisões de partículas interplanetárias com seus satélites, fragmentando-os e produzindo corpos menores. De modo sucessivo, estes fragmentos podem sofrer novas colisões e eventualmente gerar partículas de poeira. Por outro lado, os corpos macroscópicos (da ordem de metros) imersos no anel podem colidir entre si e aglutinar- se de modo a gerar novos objetos maiores. A existência destes arcos é creditada a presença de um satélite perturbador que os confina em um ressonância de corrotação. No caso do arco do anel G de Saturno, este é confinado por uma uma ressonância excêntrica 7:6 de corrotação com o satélite Mimas. Hedman et al. (2010) citam que o arco do anel G é majoritariamente composto por partículas da ordem de micrômetros. Neste caso, as forças perturbativas, tais como a pressão de radiação e a força eletromagnéticas, são significativas e tendem a reduzir o tempo de vida destas partículas nesta região. Para explicar a estabilidade do arco Hedman et al. (2010) utilizaram o pequeno satélite Aegaeon (imerso no arco) que poderia ser uma fonte do material das partículas micrométricas imersas no arco via colisões de partículas interplanetárias com Aegaeon. Entretanto, Madeira et al. (2018) exploraram o efeito da pressão de radiação solar e mostraram que o tempo de vida das partículas micrométricas no arco é menos de 40 anos e que o satélite Aegaeon não poderia ser fonte de material e manter a quantidade... (Resumo completo, clicar acesso eletrônico abaixo)<br>Abstract: Some planetary rings exhibit denser regions called arcs, and the existence of these arcs is credited by the presence of a disturbing satellite that confines the particles in a corotation resonance. The formation of the planetary ring arc can be related with the collisions between interplanetary particles with an embedded satellite, or the break up of a moon into minor bodies. Successively, these bodies may experience new collisions that eventually create dust particles. Meanwhile, the macroscopic bodies can collide among themselves and merge, resulting in large bodies. For the Saturn’s G ring’s arc, it is confined by a 7:6 corotation resonance with the satellite Mimas. Hedman et al. (2010) showed this arc is composed mostly of micrometers particles, a configuration that perturbative forces are significant and decrease the lifetime of the structure. To explain the stability of this arc, they proposed that the satellite Aegaeon could be a source of the material of the dust by collisions within interplanetary particles. However, Madeira et al. (2018) studied the solar radiation pressure and showed that the lifetime of the particles in less than 40 years and that the satellite Aegaeon cannot be a source. Therefore, another mechanism is necessary to explain the arc. To do so, one can use information derived by the LEMMS (Magnetospheric Imaging Instrument’s LowEnergy), an instrument from that Cassini spacecraft that detected an energy drop from electrons in this region, inferring t... (Complete abstract click electronic access below)<br>Mestre

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, 2014.<br>Some pages printed landscape orientation. Cataloged from PDF version of thesis.<br>Includes bibliographical references (pages 299-311).<br>The mechanisms of magma ascent and emplacement inferred from study of intrusive complexes have long been the subject of intense debate. Current models favor incremental construction, but much of this work has been focused on a single crustal level. However, the study of magmatism throughout the crust is critical for understanding how magma ascends through and intrudes surrounding crustal material. I present new field, geochronologic and geochemical data from three intrusive complexes emplaced at a range of crustal depths in the Cretaceous North Cascades magmatic arc. Integration of geological mapping and high-precision U-Pb TIMS geochronology allows me to demonstrate variable styles of intrusion in different complexes: Assembly of the Black Peak intrusive complex occurred via a series of small (<1 km 3) magmatic increments from ca. 91.7 Ma to 86.8 Ma. My data indicate each of these increments were emplaced and solidified without major assimilation of country rock. The Seven- Fingered Jack intrusive complex, emplaced around ~20-25 km, preserves a similar record of intrusion between ca. 91.8 Ma and 90.5 Ma. Significant compositional variability and antecrystic zircons suggest that the Seven-Fingered Jack represents the remnants of mid-crustal magmatic conduit. Geochronology from the deep-crustal (~25-30 km) Tenpeak intrusive complex, intruded between ca. 92.2 Ma and 89.5 Ma, suggests that plutons comprising the complex were assembled rapidly (<300 ka). These intrusive complexes represent different parts of an arc system, including deep- and shallow-crustal intrusions and a magmatic conduit. I propose a model where increments of magma migrated through the crust in magmatic conduits that were active multiple times. These conduits focused rising magma and served as a crustal filter. Geochronologic and isotopic variability between the Tenpeak and Black Peak intrusive complexes are likely a result of this filtering process and the vastly different conditions in the deep and shallow crust.<br>by Erin Kathleen Shea.<br>Ph. D.

We present the first Atacama Large Millimeter/submillimeter Array (ALMA) observations of the closest known extrasolar debris disc. This disc orbits the star is an element of Eri, a K-type star just 3.2 pc away. Due to the proximity of the star, the entire disc cannot fit within the ALMA field of view. Therefore, the observations have been centred 18" North of the star, providing us with a clear detection of the Northern arc of the ring, at a wavelength of 1.3 mm. The observed disc emission is found to be narrow with a width of just 11-13 AU. The fractional disc width we find is comparable to that of the Solar system's Kuiper Belt and makes this one of the narrowest debris discs known. If the inner and outer edges are due to resonances with a planet then this planet likely has a semi-major axis of 48 AU. We find tentative evidence for clumps in the ring, although there is a strong chance that at least one is a background galaxy. We confirm, at much higher significance, the previous detection of an unresolved emission at the star that is above the level of the photosphere and attribute this excess to stellar chromospheric emission.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1996.<br>Includes bibliographical references (p. 235-242).<br>by Françoise R. Robe.<br>Ph.D.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1994.<br>Includes bibliographical references (leaves 50-63).<br>by Alberto Edgardo Saal.<br>M.S.

Thesis: S.B., Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, 2012.<br>Cataloged from PDF version of thesis.<br>Includes bibliographical references (pages 53-56).<br>Elevated concentrations of CO₂ have been proposed as the reason that the Cretaceous climate was 6-14°C warmer than the present, however the source of Cretaceous CO₂ is unknown [Barron, 1983]. This study examines the possibility of continental arc magmatism as a mechanism for CO2 release, specifically as a volatile produced during crustal assimilation and contact metamorphism of carbonates around plutons. Bedrock maps of the North American Cordillera (a region of active continental arc magmatism during the Cretaceous), the relative locations of the carbonates, the Cretaceous plutons, and the calculated "decarbonation zones"around the plutons. These measurements were then input in a thermal and petrologoical model in order to estimate the quantity of CO₂ released by continental arc magmatism. Testing a number of cases with varying parameters, the model found the arc-magmatism-induced temperature difference between the present and Cretaceous global climates to have a lower limit of [Delta]T < 1°C and an upper limit of 5.1 < [Delta]T < 12.3°C. Decarbonation from continental arc magmatism is shown to be a possible mechanism of paleoclimatic warming, and more work is required to either confirm or refute the hypothesis.<br>by Anna Elizabeth Brunner.<br>S.B.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2004.<br>Includes bibliographical references.<br>Continental magmatic arcs are among the most dynamic. geologic systems, and documentation of the magmatic, thermal, and tectonic evolution of arcs is essential for understanding the processes of magma generation, ascent and crustal growth. The primary goal of this research is to determine rates of tectonic and magmatic processes in the mid to deep crustal levels of the crystalline core of the Cretaceous North Cascades arc. This region was selected for study because it preserves a -10-40 km depth-section through the arc, which allows an assessment of magmatic and structural processes over a range of crustal levels. The relatively young age of the arc (ca. 100-45 Ma) and the inherent high-precision of U-Pb zircon dates permit absolute uncertainties of <100 ky. Meta-supracrustal rocks of the Cascades core record some of the highest pressures obtained in the North American Cordillera. The timing of deposition and metamorphism of the 9-12 kbar Swakane Gneiss constrain tectonic burial models and the timescales of large crustal displacements within an arc setting. These models involve rapid burial (-7 mm/yr) of a fore- or back-arc basin from ca. 73-68 Ma. Nd isotopic signatures of all meta-clastic terranes of the Cascades core reflect mixing of arc- and craton-derived sediment, and the Swakane Gneiss has the most isotopically-evolved signature of these terranes. Nd isotopic signatures of plutons that intrude the core lack evidence of melting of this isotopically-evolved unit. 40Ar/39Ar and U-Pb thermochronologic data define regional cooling patterns that suggest mid- to Late Cretaceous exhumation coincident with contraction and crustal thickening at the deepest levels of the core, followed by Early Tertiary extension.<br>(cont.) High-precision U-Pb geochronology reveals internal complexities inherent in the construction of an intrusive magmatic system. The Mount Stuart batholith was constructed over a ca. 5.6 Myr time period with four punctuated intervals of magma emplacement, whereas the Tenpeak intrusion was emplaced in a more continuous process over ca. 2.7 Myr time period. U-Pb zircon dates from two elongate intrusions, the Seven- Fingered Jack and Entiat suites, suggest that they were constructed from multiple magmatic sheets that were partially homogenized at the level of emplacement.<br>by Jennifer E. Piontek Matzel.<br>Ph.D.