QUESTION:
How big is Planet X?

ANSWER from Bob Loewenstein on October 20, 1995:
Most astronomers no longer believe that there is a 'Planet X'. Originally,
some people thought that another large planet had to exist to explain some
small irregularities in Uranus' orbit. However, in new models done by
scientists at the Jet Propulsion Laboratory (JPL), where more accurate data
for the masses of Jupiter, Saturn, Uranus, and Neptune were considered, all
the small irregularities can be explained by the known solar system objects.

So, Planet X seemed like a nice idea at the time, like the search for
Neptune. But with new information, we find that there is no need to invoke
the idea of Planet X anymore.