High-order librations of Halley-type comets
Halley-type comets, usually referred to as those with revolution periods of 20 to 200 yr, can be dynamically defined by the values of their Tisserand invariants with respect to Jupiter, which account for the processes that brought these comets into the present orbits. Long-term integrations of their motion show oscillations of their heliocentric elements when the comets are far from the Sun and the centre of their motion is the barycentre of the solar system. The shift from barycentric to heliocentric motion is also responsible for the major changes of orbital elements within a single revolution which, in the case of direct orbits, may follow regular libration patterns with typical periods of 350–400 yr. This is the reason for the concentration of periods around 70 yr. Some examples of this behaviour and a short discussion of its importance for the dynamical history of Halley-type comets are presented.
Key wordscomets Halley-type comets resonances
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