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2008 Annual Science Report

University of Hawaii, Manoa Reporting  |  JUL 2007 – JUN 2008

Origin of Irregular Satellites

Project Summary

An interesting feature of the giant planets of our solar system is the existence of regions around these objects where no irregular satellites are observed. Surveys have shown that, around Jupiter, such a region extends from the outermost regular satellite Callisto to the vicinity of Themisto, the innermost irregular satellite. This project aims to understand the reason for the existence of such a satellite—void region by numerically integrating the orbits of several hundred small objects, distributed in a region between 30 and 80 Jupiter-radii.

4 Institutions
3 Teams
0 Publications
0 Field Sites
Field Sites

Project Progress

Due to their proximity, the irregular satellites of Jupiter have been subjects of extensive observational and theoretical research. As shown by Sheppard & Jewitt (2003), the region extending from the orbit of Callisto at 26 Jupiter-radii (RJ), to the periastron of Themisto (?76RJ), is void of irregulars. The focus of this project is on understanding the reason for the lack of irregular satellites in the boundary between regulars and irregulars. We numerically integrated the orbits of several hundred test particles in a region interior to the orbit of Themisto. We assumed that the regular satellites of Jupiter were fully formed and studied the perturbative effects of the Galilean satellites on the dynamics of small objects. Our simulations showed that, except at large distances from Ganymede and Callisto, the lack of irregular satellites can be attributed to the instability of these objects caused by their interactions with the two outermost Galilean satellites (Figure 1). At larger distances (e.g., between <40RJ and 80RJ for particles in circular orbits, and between <60RJ and 80RJ for particles with initial orbital eccentricities of 0.4), the perturbations of Galilean satellites do not seem to be able to account for the instability of small bodies. A possible explanation is that their instability is the result of interactions with Jovian satellitesimals and protosatellites during the formation of Jupiter’s regular moons. Figure 2 shows the region of stability of Jovian irregular satellites obtained from our numerical simulations. As shown here, this region coincides with the region where irregular satellites actually exist.

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    Nader Haghighipour Nader Haghighipour
    Project Investigator
    David Jewitt David Jewitt
    Objective 1.1
    Models of formation and evolution of habitable planets