Before the discovery of Pluto in
the 20th century, it had been
theorized that a ninth planet,
Planet X, existed beyond
Neptune due to the
gravitational clustering that
could only be caused by a
massive object. It was then
believed that this planet was
found in Pluto, but that never
fully quantified the gravitational
distortion until scientists at the
California Institute of
Technology presented evidence
that a ninth planet truly does
exist with an orbital period of
15,000 years.
The astronomers who
published their discovery have
calculated that there is “ only a
0.007 percent chance, or about
one in 15,000, that the
clustering could be a
coincidence.” Presently, Planet
Nine remains hypothetical, but
astronomers have calculated its
orbit to be quite massive. If it
does exist, the planet would
likely be approximately 2–15
times the mass of Earth and
orbit between 200 and 1,600
Astronomical Units (AU) from
the Sun. An AU is 150,000,000
kilometers, which means that
the planet could orbit as far
from the Sun as
240,000,000,000 kilometers.