Well, Pluto is considered a planet, a dwarf planet, which is basically an asteroid or comet, but that doesn't really count, now does it?
I imagine the people who made this decision are getting some death threats.

This is our solar system no more.

R.I.P Pluto the ninth planet.
And they spent all that money to send that probe to the nineth planet. Now Nasa's just exploring a worthless rock. Good job.
An Official Definition of planets, dwarfs, and other objects
RESOLUTION 5A
The IAU therefore resolves that planets and other bodies in our Solar System be defined into three distinct categories in the following way:
(1) A planet1 is a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and (c) has cleared the neighbourhood around its orbit.
(2) A dwarf planet is a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape2, (c) has not cleared the neighbourhood around its orbit, and (d) is not a satellite.
(3) All other objects3 orbiting the Sun shall be referred to collectively as "Small Solar System Bodies".