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Two Irregular Satellites of Jupiter

23 Nov 2012, 13:25 UTC
Two Irregular Satellites of Jupiter
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The planetary satellites can be distinguished into two characteristic groups: regulars and irregulars. Satellites are classified as “irregular” when their orbits are large, highly elliptical and tilted with respect to the equators of their host planets. In contrast, so-called regular moons, such as Earth’s or the large Galilean satellites of Jupiter, are characterized by small values of semi-major axis, eccentricities and inclinations. Moreover, most of the irregulars have retrograde orbits, which means they move around their host planet in a direction opposite to the sense of the rotation of the planet. While in contrast, regular moons have prograde orbits. Another important characteristic of the irregular ones are the family groups, i.e., satellite groups characterized by similar orbital elements.This difference can be traced directly to different modes of formation. Whereas the regular satellites grew by accretion within circumplanetary disks, the most plausible hypothesis to explain the origins of the irregular satellites is that they formed elsewhere and were captured by the planet from initially heliocentric orbits at an early epoch. While different capture mechanisms have been suggested (Gas drag capture; Pull-Down capture; Close-approach interaction captures; Capture of binary-asteroids) these bodies are still not well explained by standard models. Studying the origins ...

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