The search for Planet X started
in 1841 when astronomers noticed that
Uranus did not move as predicted in it's orbit. Based on these residuals
the search for Planet X began. Neptune was found in 1846 and when
Neptune's moon Triton was discovered later that year astronomers were
able to determine the size of Neptune. They found that it was 2% larger
than expected which indicated another planet may exist. Many searches
were done and in 1930 Clyde Tombaugh discovered Pluto. Pluto did not
seem massive enough to have caused the differences between the
calculated orbit and the observations. Tombaugh searched 13 more
years, photographing almost the entire sky visible from the northern
hemisphere. He searched to 50 degrees below the ecliptic down to a
very faint magnitude 18.
In 1978 when Pluto's moon Charon
was discovered it was confirmed
that Pluto/Charon could not have caused the observed deviations in
the orbits of Uranus and Neptune.
In the late 1970's and 1980's
the search gained strength. Robert
Harrington and Tom Van Flandern of the United States Naval
Observatory (among others) proposed several theories and conducted
searches. Nothing was found. None of these theories were even remotely
like the fantastic Zeta Planet X. These theories prompted various news
articles about Planet X that are still used as proof of their phantom planet.
Zetatalk on the 1980's news stories
In 1989 the first and only space
probe to visit Neptune, Voyager 2
gave more accurate readings of the mass and determined that Neptune
was .5% smaller than previously thought. That is quite a large difference,
remember the hunt for Planet X started because Neptune was thought
to be 2% larger then predictions.
In 1992, Dr. Myles Standish used
the updated mass in his calculations
and determined the perturbations actually didn't exist. The recorded
observations matched the predicted orbits when the correct values of
mass were put into the equations.
NYTimes article on Myles Standish and Planet X
Planet X: No Dynamical Evidence in the Optical Observations
So the answer to the question
is NO, the outer planets are not being
perturbed. It was originally thought that Planet X existed because Neptune
was 2% larger than expected. The discovery that it was .5 smaller than prior
estimates along with updated mass figures for the other outer planets
(also by Voyager 2) discounted signs of a large planet. Astronomers now
believe that any small differences are the result of many large asteroids in
the outer solar system. It is also notable that Zetatalk seems to believe the
math that showed these perturbations, but the same math which shows their
planet does not exist is ignored.