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Project Progress

One of the main features of all the giant planets of our solar system is the possession of irregular satellites. These objects, that unlike regular satellites, have highly eccentric orbits, and/or are on high orbital inclinations, are thought were captured from bodies that were formed elsewhere in the solar system. The accretional process of the formation of regular satellites in a circumplanetary disk cannot account for the high eccentricity and inclination of the orbits of these bodies.

Thanks to the wide field CCD devices, during the past few years, a wave of discoveries was made which resulted in an unprecedented increase in the number of detected irregular satellites. The results of these observations have revealed many new features and characteristics of these objects. Mauna Kea survey observations of Jovian irregulars have, for instance, indicated that the region between Callisto (the outermost regular satellite at semimajor axis of ~26 Jupiter-radii) and Themisto (the innermost Jovian irregular at approximately 100 Jupiter-radii), is devoid of small objects. An explanation for this observation may lie in the dynamical nature of small bodies in this region. That is, these objects may be intrinsically unstable. To examine this scenario, in collaboration with David Jewitt from NAI/Hawaii, N. Haghighipour initiated an extensive numerical study of the orbital stability of small bodies in the region between 30 to 80 Jupiter-radii. We simulated the dynamics of a large battery of small objects and mapped their parameter-space for different values of their semimajor axes, eccentricities, and orbital inclinations. Results indicate that this region is indeed intrinsically unstable. However, the lifetimes of objects vary with their orbital eccentricities and inclinations. These results also make possible identifying the most viable capture mechanism of irregular satellites, and have applicability in furthering our understanding of outer planets formation history.