"Planet X" is a hypothetical planet that some scientists believe exists in our solar system, beyond the orbit of Neptune. It is thought to be much larger than Earth and could explain certain unusual gravitational effects observed in the orbits of distant trans-Neptunian objects. The search for Planet X has sparked interest and debate among astronomers. While some evidence suggests its existence, no direct observations have confirmed it yet. Researchers continue to study the outer solar system, hoping to find more clues about this mysterious planet and its potential impact on our understanding of planetary formation.