Originally posted by bismarck:
if they are undiscovered, how come tehre are sites abt it ?
From what I gather, planet X is half myth half science. Astronomers are concerned that something else is affecting the orbits of the existing 9 planets and the 10th planet (Sedna or this 2003) ain't big enough to affect the orbits. Thus from this gravitational effect, astronomers hypothised that there must be another big undiscovered planet out there.
Myth wise, many ancient civilisations recorded alien visitors from this planet X. Think the Egyptians or the babylonians called it Niribu.