Eccentricities of planets in multi-planet extra-solar systems: Insights from classical secular theory.

Speaker: 
Christa Van Laerhoven
Event Date and Time: 
Mon, 2015-03-02 15:30 - 16:30
Location: 
Hennings 318
In planetary systems with more than one planet, gravitational
interactions cause orbital eccentricity variations. For non-resonant
systems, classical secular theory reveals that the eccentricities are
vector sums of contributions from several eigenmodes. The structure of
these secular eigenmodes can be calculated from the star and planet
masses and the planets' semi-major axes. Thus, the secular eigenmodes
can offer valuable insight into the long-term eccentricity behavior of
planets, even without knowing the current eccentricities. Examination
of the eigenvectors often reveals subsets of planets that interact
especially strongly as dynamical groups. I will discuss dividing
planets into those who are dynamically grouped together ('groupies')
and those who are dynamically uncoupled ('loners').

Perturbations from other sources, such as tides, are shared among the
planets through the secular interactions. If one planet's eccentricity
is tidally damped, all the eigenmodes damp so as to leave a signature
on their amplitudes. The tidally perturbed planet may retain a
substantial eccentricity because some eigenmodes that contribute to
its eccentricity will be longer-lived. Tides also affect evolution of
planets' semi-major axes, which is coupled with eccentricity
evolution. Thus, tidal evolution of planets in a multi-planet system
is qualitatively different from tidal evolution of single planets.
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