Institute for Advanced Study/Princeton University Joint Astrophysics Colloquium

Several lines of evidence, both theoretical and observational, indicate that additional planets in the outer solar system remain to be discovered. Most recently, attention has been focused on 'Planet Nine',a few Earth mass planet with a moderate inclination at a distance of a few hundred AU (Trujillo & Sheppard 2014, Batygin & Brown 2016, Brown & Batygin 2016). I will review this evidence for the existence of this body and will present a variety of approaches that are being used to find it.