The classical principle of least action says that orbits of mechanical systems extremize action; an important subclass are those orbits that minimize action. In this paper we utilize this principle along with Aubry-Mather theory to construct (Birkhoff) regions of instability for a certain three-body problem, given by a Hamiltonian system of degrees of freedom. We believe that these methods can be applied to construct instability regions for a variety of Hamiltonian systems with degrees of freedom. The Hamiltonian model we consider describes dynamics of a Sun-Jupiter-comet system, and under some simplifying assumptions, we show the existence of instabilities for the orbit of the comet. In particular, we show that a comet which starts close to an orbit in the shape of an ellipse of eccentricity can increase in eccentricity up to . In the sequels to this paper, we extend the result to beyond and show the existence of ejection orbits. Such orbits are initially well within the range of our solar system. This might give an indication of why most objects rotating around the Sun in our solar system have relatively low eccentricity.
"Destruction of invariant curves in the restricted circular planar three-body problem by using comparison of action." Duke Math. J. 159 (2) 275 - 327, 15 August 2011. https://doi.org/10.1215/00127094-1415878