Earlier this week, two astronomers at Caltech announced that they had observational evidence of a ninth planet orbiting in the far reaches of the Kuiper Belt. The planet has not been directly detected but its effect on the orbits of six dwarf planets was observed. Based on theoretical models, the most likely explanation for the unexpected orbits of these icy bodies is a planet, 5 to 10 times the mass of Earth. They're calling it Planet Nine, but I remember when I first became interested in Astronomy at 7 years old, reading about the mysterious "Planet X" that many believed orbited somewhere in the Kuiper Belt. The story of the search for Planet X and other far orbiting bodies is apparently far from over.
