JAN 21, 2002 - Planet X is the working moniker given to a hypothetical tenth planet of the solar system, lying somewhere outside the orbit of Neptune. It's also the short title of a May 1993 article by E. Myles Standish in The Astronomical Journal, which is presented in its entirely here online courtesy of The NASA Astrophysics Data System. The full title of the article pretty well summarizes the sad news for all you Planet X fans: "Planet X: No Dynamical Evidence in the Optical Observations". If you'll recall, the search for Planet X owes its origin in the first place to so-called "unexplained anomalies in the motion of Uranus". Standish shows in this article that these anomalies disappear when the correct value for Neptune's mass is accounted for. Likewise, apparent irregularities in Neptune's observed positions over time are accounted for by known elements of the solar system. The bottom line: "there remains no need to hypothesize the existence of a tenth planet in the solar system."
Technical note: Web Site Garage rates Planet X fair over-all, poor in load time (26.84 seconds with a 56k modem). In comparison, the page you're now reading rates excellent in both categories, loading in 5.90 seconds at 56k.
