Du 18 juin 2018 au 22 juin 2018
Strasbourg, France

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Planet 9 in the Solar System? Why is it necessary, and how could we discover it?

Le 4 décembre 2017
De 10h00 à 12h00

Hervé Beust


In a now famous paper, Batygin & Brown (2016) claimed that the orbital configuration of the outermost scattered Kuiper belt objects (KBOs) discovered so far imply the presence of an additional, external ~10 Earth masses unknown planet orbiting the Sun at large distance (~700 AU) on a very eccentric orbit (e~0.6). This planet would trigger orbital confinement of the external KBOs via its gravitational perturbations. I will review this issue, and show that the initial analysis of Batygin & Brown (2016) was partly erroneous, due to the use of a too crude approximation of the interaction Hamiltonian. In particular, they claimed that the KBOs under consideration need to be in mean-motion resonance with the unknown planet (furthermore referred to as Planet 9). I show that this is not necessary (Beust 2016). In fact, the model of Batygin & Brown (2016) actually works better than they initially thought. I will then review the subsequent work that was done on the Planet 9 hypothesis, and the consequences of its presence for the Solar System dynamics. I will also detail the issues concerning the strategy and techniques that will need to be used to try to discover this still hypothetical object.

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