Only dwarfs orbiting further than Neptune can be classified as a plutoid, and
they must also circle the sun and be large enough to have their own
gravitational field. Pluto's permanent classification as a plutoid now
means Neptune is the outermost planet in Earth's solar system; one complete
orbit around the sun takes almost 165 years.
are celestial bodies in orbit around the sun at a distance greater than
that of Neptune that have sufficient mass for their self-gravity to overcome
rigid body forces so that they assume a hydrostatic equilibrium
(near-spherical) shape, and that have not cleared the neighborhood around their
orbit," said the IAU.
Pluto and Eris remain the only plutoids at the moment, but astronomers expect
to find other small bodies that meet the qualifications to be a plutoid.
The controversy over Pluto's planet status has been strong for years, and the
IAU-created plutoid classification most likely will not end the debate.
In fact, it is unlikely the debate regarding Pluto's status and what it should
be classified as will never end, and defining it as a "plutoid" will
only add fuel to the fire.
Many astronomers remain angry that Pluto, considered a planet for around 70
years, could have its status demoted so easily by the IAU. Text book
publishers and teachers must now begin to teach students that Pluto lost its
planet status and is now a plutoid, along with describing the new
The IAU has been the sole organization responsible for classifying all
planetary bodies for more than a decade.
quote: Ceres is located much closer to the sun than Pluto and is also large enough to maintain a spherical shape. Why not call it a planet as well then?