Pluto, UB313, and VB12 (Sedna)

A little bit about Pluto: Part of the Kuiper Belt (region of frozen objects beyond Neptune) Considered ice dwarf Orbit is eccentric compared to other planets:

A little bit about UB313: Discovered in 2003 Roughly about 2x the size of Pluto 97 AU’s from sun Surfaced with methane ice like Pluto

A little bit about Sedna (VB12): Extremely elliptical orbit ¾ size of Pluto NOT a Kuiper Belt Object

Definition of a planet? There is no REAL definition of what a planet is…  Purely historical. Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, and Pluto are planets. Nothing else in the solar system is a planet.  Historical plus. Mercury through Pluto are planets, as is any newly discovered object larger than Pluto.  Gravitational rounding. Any object which is round due to its own gravitational pull and which directly orbits the sun is called a planet.  Population classification. Just like the solar system very naturally divides itself between round objects and non-round objects, it also very naturally divides itself between solitary individuals and members of large populations.

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