It seems the what-is-a-planet debate is heating up again. A relatively new proposal to me is that if you have a sufficiently large body, with strong enough gravity, to form a roughly spherical shape, that can be called a planet. That would allow Pluto (and Charon) into the planet club again. I heard that this (or a similar) proposal ignores an orbital aspect, saying the body must orbit the Sun. That seems odd for then that would make moons of planets considered planets. And that doesn't sit with me.
Kirby Runyon's definition is noted in an
article at Universe Today. His definition includes any non-fusion body. That could mean that our solar system then has over 100 planets!
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Image from Emily Lakdawalla of the Planetary Society, data from NASA / JPL, JHUAPL/SwRI, SSI, and UCLA / MPS / DLR / IDA, processed by Gordan Ugarkovic, Ted Stryk, Bjorn Jonsson, Roman Tkachenko, and Emily Lakdawalla.
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