Is This A Proper Definition Of A Planet and A Complete List Of Known Planets In Our Solar System?

Question

A planet is any object that orbits the Sun without also orbiting another object and is large enough for its mass to have pulled it into a spherical or round shape.The planets are:Mercury Venus Earth Mars Ceres Jupiter Saturn Uranus Neptune Pluto Charon Eris.Twelve in all.

Answer 1

Yes

Answer 2

This was the proposed definition and list of planets going into the IAU meeting in Prague two years ago.  The eventual vote added a thrid criterion about having gravitational dominance (the phrase used was "cleared the neighbourhood of its orbit") with the result that only 8 bodies met the definition of planet (Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune.)  Ceres, Pluto and Eris are considered "dwarf planets" (they meet your 2 criteria but not the third.)  Pluto and Eris (and Makemake) are considered to be in a special category of dwarf planets called "plutoid."  Charon is still classified as a natural satellite or moon.

Now some people, including some astronomers would agree that your definition does indeed make sense.  I think they would probably still exclude Charon as a moon but they might add a few other names of bodies that in all likelihood are spherical due to the influence of gravity.  

Answer 3

Ceres, Eris and Pluto are called dwarf planets. But Charon is not considered as a planet. It is simply a moon of Pluto, which is roughly twice of the size of Charon. Your definition of a planet is simply correct though. Im not an astronomer...LOL

Answer 4

No, the definition has the problem, that it does not include the dominance of the object over the neighboring objects. This factor is not too unimportant, as there can be many accidentally spherical objects, which might not be in a stable orbit, but get slung around the solar system by swing-by events.

Charon and Pluto would also not count in your list according to your own rules: Both don't orbit the sun, but rotate around a point between them, making them a binary planet.  

Answer 5

YEAH

Answer 6

You didn't mention Sedna. OVER TIME, she MAY settle into a more regular orbit.  To use a metaphor, we have only been watching through a hole in the fence for five minutes, it is little early to declare we have the timetable for the whole railway network!  I can see why you want to tidy things up, it would be nice, but probably in error, and we have the IAC to do this for us.