What is Planet Nine, and where is it? Mystery of large hidden planet beyond Neptune explained

What is Planet Nine, and where is it? The question has fascinated astronomers for years. Scientists believe a massive undiscovered planet may exist in the outer Solar System. Although no telescope has directly observed it, unusual movements of Kuiper Belt objects, Extreme Trans-Neptunian Objects, sednoids, and other distant bodies continue to fuel the Planet Nine theory and ongoing searches.