We don't know for sure, although it is possible that there may be a large object that can be detected in the future. However, astronomers have not as yet been able to find Planet X. Pluto was discovered by Clyde Tombaugh on February 18, 1930. Although many searches have been done with the help of infrared telescopes, several hundred candidates that were thought to be Planet X have been found to be either stars or galaxies.