Planet Nine from Outer Space: A Status Update

<!--HTML-->b'<p><span><span>Over the course of the past two decades, observational surveys have unveiled the intricate orbital structure of the Kuiper Belt, a field of icy bodies orbiting the Sun beyond Neptune. In addition to a host of readily-predictable orbital behavior, the emerging census of&nbsp;trans-Neptunian objects appears to display dynamical phenomena that cannot be explained by interactions with the known eight-planet Solar System alone. Specifically, the observed physical clustering of orbits with semi-major axes in excess of <span>&#8764;</span> 250 AU, the detachment of&nbsp;perihelia of select Kuiper belt objects from Neptune, as well as the dynamical origin of highly inclined/retrograde long-period orbits remain elusive within the context of the classical view of the Solar System. This newly outlined dynamical architecture of the distant solar system&nbsp;points to the existence of planet with mass M9 <span>&#8764;</span> 5M<span>&#8853;</span> on a moderately inclined orbit with a semi-major axis a9 <span>&#8764;</span> 400&#8722;800 AU and eccentricity e9 <span>&#8764;</span> 0.4&#8722;0.6. In this talk, I will review the observational motivation, dynamical constraints, and prospects for detection of this proposed&nbsp;object known as Planet Nine.</span></span></p>'