For over a century, astronomers have been fascinated by the idea of a hidden planet lurking in the farthest corners of our solar system. This concept began in the 19th century when Neptune was discovered through mathematical predictions based on gravitational disturbances in the orbit of Uranus. This success inspired searches for a hypothetical "Planet X," a ninth planet that might explain other gravitational anomalies. Though Pluto was discovered in 1930, it was later reclassified as a dwarf planet in 2006, reigniting the search for a true ninth planet. Today, scientists continue to investigate whether such a planet exists, with some confident that its discovery could be on the horizon. The idea of a ninth planet, sometimes called "Planet Nine," traces back to the early 20th century when astronomer Percival Lowell suggested that strange orbital patterns of Uranus and Neptune could be caused by an unseen planet. While Lowell’s Planet X was a precursor to the modern Planet Nine concept, the two differ in focus. Early efforts to find Planet X looked at the motion of the giant planets, but later data, including NASA's Voyager 2 mission in the 1980s, suggested these anomalies could be explained without an additional planet. This led scientists to shift their attention to smaller, distant objects beyond Neptune. In recent years, astronomers have focused on the unusual orbits of extreme trans-Neptunian objects (ETNOs), which are icy bodies found far beyond Neptune. In 2016, researchers at Caltech, Konstantin Batygin and Michael Brown, proposed that an undiscovered planet, roughly the size of Neptune, could explain the strange clustering of these ETNOs. More recent studies, including those from 2024, have examined how these objects move in relation to Neptune’s orbit. Batygin argues that these objects are dynamically unstable and must be continually replenished, a process that Planet Nine could naturally explain. Other models, he says, struggle to account for the data once observational biases are considered. Batygin explains that Planet Nine could account for several puzzling features in the outer solar system, such as the clustering of orbits, the unusually large distances of some objects from the Sun, and the presence of bodies moving in opposite or highly tilted directions. While no direct image of Planet Nine has been taken yet, the growing number of observed ETNOs supports the idea that a massive planet is influencing them. Batygin believes that with upcoming powerful observatories like the Vera C. Rubin Observatory, the missing evidence could soon be found. He also cautions that the data is complex, and the clustering of objects doesn’t necessarily mean all of them are influenced by the same planet. The search for Planet Nine remains an open question, much like the search for Planet X in the early 20th century. While the idea is compelling, it still requires a direct observation to be confirmed. As more advanced telescopes come online, the possibility of finding this hidden planet—or discovering an alternative explanation—grows stronger. Until then, Planet Nine continues to be a captivating mystery, offering the chance to expand our understanding of the solar system.