Planet X, the Sumerian's 12th Planet

Observable Comets (orbital elements data)

Cometary Orbit Viewer (Java Applet from AstroArts)

A History of Planet X

Planet X Orbit

Map of Planet X Orbit

Mystery Heavenly Body Discovered, a front page story in Washington Post

No Tenth Planet Yet From IRAS

The Search for Planet X

Lost Worlds - Planets without a sun (CNN)

Astronomical Interpretations

The Mathematical Problem of the Earth Orbit's Precession-Time Paradox

No Tenth Planet Yet From IRAS

Zetatalk

Dark Star Theory

John Anderson about Planet X