Planet Nine is a hypothetical planet in our solar system, believed to be located far beyond the orbit of Neptune. Scientists propose that it could be about 10 times the mass of Earth and take thousands of years to complete one orbit around the Sun. The existence of Planet Nine is suggested by unusual patterns in the orbits of distant objects in the Kuiper Belt, a region filled with icy bodies. Researchers are actively searching for this elusive planet using advanced telescopes and computer simulations to better understand its potential impact on our solar system.