I know some have probably heard, but there are no longer nine “planets” in our solar system. Being the astronomy buff that I am, I have been keeping track of this on the side… I’m just now getting around to writing about it though. 
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It doesn’t really bother me much since I’ve always felt “why is this thing that is smaller than our moon a planet?” I also know that “science” can and will change constantly… whether it be brand new discoveries or new discoveries about old “facts”, science changes.
So, at the end of the “General Assembly for the International Astronomical Union” on the 24th, they reached a new definition of the word “planet”
It is, as follows:
(1) A “planet”1 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 except satellites orbiting the Sun shall be referred to collectively as “Small Solar-System Bodies”.
_______________________________1The eight planets are: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune.
2An IAU process will be established to assign borderline objects into either dwarf planet and other categories.
3These currently include most of the Solar System asteroids, most Trans-Neptunian Objects (TNOs), comets, and other small bodies.
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Yes, Pluto is a “planet” no more… it is now a “dwarf planet”.
…here’s a link to the official IAU website where they have this posted: LINK
Cheers!
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