So 10 happy planets… or is that 8 happy planets and 2 (well, 5 really) happy Kuipter Belt planets?

There just isn’t a formal astronomical definition for a planet.    There is, however  a dictionary definition:

1. A nonluminous celestial body larger than an asteroid or comet, illuminated by light from a star, such as the sun, around which it revolves. In the solar system there are nine known planets: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, and Pluto.
2. One of the seven celestial bodies, Mercury, Venus, the moon, the sun, Mars, Jupiter, and Saturn, visible to the naked eye and thought by ancient astronomers to revolve in the heavens about a fixed Earth and among fixed stars.
3. One of the seven revolving astrological celestial bodies that in conjunction with the stars are believed to influence human affairs and personalities.

So there is little consensus on what this thing should be called, but general agreeance it seems that its at least as big as Pluto, and up to twice Pluto’s size.    They’ve been lookin for something bigger than Pluto for like 75 years now.

In any case, there seems to be a plethora of massive snowballs out there.   Lets send probes.  Armies of probes.

Lets wait and see if any Mars (or even Earth/Venus) sized worlds are detected.    Now that we know we should be looking off the main plane of the solar system.

http://www.space.com/scienceastronomy/050729_new_planet.html