Propriedades fotométricas da superfície de Pequenos Corpos

Abstract

The two main Small Body populations, asteroids and comets, present different physical-chemical caracteristics on their surfaces. Most of the studies of their surfaces is based on the observation of integrated light from Earth telescopes. Up to now, only 13 objects have been visited and monitored in details by space missions. Therefore, the goal of the present thesis is the study of individual and collective surface proprieties based on photometric data of Small Bodies of the Solar System. The photometry allows to obtain information on topography and variegations in high angular resolution. Pursuing the study of collective proprieties we use the largest photometric catalog of asteroids, the Sloan Digital Sky Survey Moving Object Catalog 4. We transform the reflectances of three samples into the principal components space and we notice two distinct continuous trends of feature and featureless asteroids. Hence, we propose a new classification system for spectro-photometric data of asteroids based on both continuities. For the individual study, we work with images ranging from 270 to 989 nm obtained by the OSIRIS system on-board Rosetta for two representative objects of Small Bodies population: the asteroid (21) Lutetia and the mission target, the comet 67P/Churyumov–Gerasimenko. For (21) Lutetia, we focus on the Baetica region. The region bears a cluster of superimposed craters that shows most of the variegations in the North pole. There, we study the correlations between spectrophotometry and the Hapke parameters of the regolith. The analysis vi reveals a dichotomy between the crater walls, possibly related to small differences on their regolith. For comet 67P/Churyumov–Gerasimenko, we undertook a global photometric study of the images obtained during the rendez-vous stage. The opposition effect and phase reddening are, for the first time, observed in a cometary nucleous. We are able to discern spectro-photometric variability in the surface of the nucleous and classify it into three groups according to spectral slope and location. We finally conclude discussing the implications of the obtained result for the composition, formation and transformation of the regolith in the surface of the Small Bodies of the Solar System.