Free Astronomy Magazine September-October 2022

34 SEPTEMBER-OCTOBER 2022 ASTRO PUBLISHING by Michele Ferrara revised by Damian G. Allis NASA Solar System Ambassador Planet Nine increasingly unreachable A stronomers have been search- ing for a large trans-Neptun- ian planet for over a century. This search began when they deter- mined that Neptune's mass and or- bital properties were inadequate to explain the anomalies previously found in the orbital motion of Uranus, whose position in the sky appeared to deviate from theoreti- cal calculations. The belief that an- other planet should exist grew further after the almost accidental discovery of Pluto, whose mass turned out to be too small to signif- icantly influence the motion of Uranus or the orbit of Neptune, it- self also not perfectly respectful of the astronomical calculations of the time. However, it became evident in the early 1990s that the anomalies detected in the positions of the two icy giants could be explained even F antasy representation of the hy- pothetical Planet Nine as seen from very far from the rest of the solar system, which appears as a patch of indistinct light on the side.