Estudo da estabilidade do anel de Jano e Epimeteu
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Data
2012-08-13
Autores
Souza, Alexandre Pinho dos Santos [UNESP]
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Universidade Estadual Paulista (Unesp)
Resumo
Em Setembro de 2006 foi descoberto um anel tênue na mesma órbita dos satélites Jano e Epimeteu. Simulações numéricas indicaram que o tempo de vida deste anel seria de poucas décadas. A partir dessa constatação foi considerado como improvável que o anel tenha sido observado pela sonda Cassini no curto período de vida do anel, veri cado pelas simula ções. Logo, faz-se necessário a existência de um mecanismo que explique a estabilidade do anel. A criação de partículas para aneis por meio de ejeções dos satélites próximos é uma possível fonte de material. Para veri car esse fato é necessário comparar resultados experimentais (fotometria) com resultados teóricos baseados no modelo de produção de partículas via colisões. A grandeza a ser comparada é o I/F que representa a intensidade de radiação captada pelo detector proveniente do alvo espalhador. Por meio da fotometria das imagens foi possível obter o valor experimental de I/F. Já, o valor do I/F teórico foi obtido por meio de um modelo que converte as distribuições de partículas em termos da grandeza profundidade óptica. Para a obtenção desses valores de profundidade óptica foram necessários resultados de simulações numéricas (com pressão de radiação solar) que indicam a relação do tempo de vida das partículas no sistema relacionado com seus respectivos tamanhos. Além da profundidade óptica, esse valor teórico depende do ângulo de transmissão e a função de fase, cujo valor foi obtido por meio do calculador Wiscombe para espalhamento Mie. Os valores de I/F teórico e experimental foram comparados e os resultados encontrados, para as considerações adotadas no trabalho, mostram que não é possível justi car a estabilidade do anel por meio de colisões...
In September of 2006 a faint ring was discovered at the same orbit of the satellites Janus and Epimetheus. Numerical simulations indicated that the lifetime of this ring would be just a few decades. Due to this veri cation it was considered improbable that the ring was detected by the Cassini spacecraft in the short period of time forseen by the simulations. Thus it is necessary to exist a mechanism that explains the stability of the ring. The creation of particles to the ring by ejections from close satellites is a possible source of material. In order to certicate this possibility it is necessary compare experimental results (photometry) with theoretical results based on a collision particles production model. The quantity to be compared is I/F, that represents the intensity of radiation that comes from the scattering object captured by the detector. Using the photometric results of the images it was possible to get the experimental value of I/F. However, the value of theorical I/F was obtained by a model that converts particles distributions in optical depth. In order to get these values of optical depth it was necessary some new results of numerical simulations (including Solar radiation pressure) that show the relation between lifetime and size of the particles in this system. Besides the optical depth, the transmission angle and the phase function, whose value is obtained by the Wiscombe calculator for Mie scattering, are required to obtain the nal value of the theoretical I/F. The values of theoretical and experimental I/F were compared and results that have been gotten under the considerations of this research indicate that it is not possible to explain the stability of this ring just by this collisions model. So the collisions do not... (Complete abstract click electronic access below)
In September of 2006 a faint ring was discovered at the same orbit of the satellites Janus and Epimetheus. Numerical simulations indicated that the lifetime of this ring would be just a few decades. Due to this veri cation it was considered improbable that the ring was detected by the Cassini spacecraft in the short period of time forseen by the simulations. Thus it is necessary to exist a mechanism that explains the stability of the ring. The creation of particles to the ring by ejections from close satellites is a possible source of material. In order to certicate this possibility it is necessary compare experimental results (photometry) with theoretical results based on a collision particles production model. The quantity to be compared is I/F, that represents the intensity of radiation that comes from the scattering object captured by the detector. Using the photometric results of the images it was possible to get the experimental value of I/F. However, the value of theorical I/F was obtained by a model that converts particles distributions in optical depth. In order to get these values of optical depth it was necessary some new results of numerical simulations (including Solar radiation pressure) that show the relation between lifetime and size of the particles in this system. Besides the optical depth, the transmission angle and the phase function, whose value is obtained by the Wiscombe calculator for Mie scattering, are required to obtain the nal value of the theoretical I/F. The values of theoretical and experimental I/F were compared and results that have been gotten under the considerations of this research indicate that it is not possible to explain the stability of this ring just by this collisions model. So the collisions do not... (Complete abstract click electronic access below)
Descrição
Palavras-chave
Astronomia, Colisões (Fisica nuclear), Astronomy
Como citar
SOUZA, Alexandre Pinho dos Santos. Estudo da estabilidade do anel de Jano e Epimeteu. 2012. 218 p. Dissertação (mestrado) – Universidade Estadual Paulista, Faculdade de Engenharia de Guaratinguetá, 2012.