What’s wrong with Pluto?

With NASA’s New Horizons probe 1 approaching Pluto on a fly-by with closest approach on track for July 14th, I thought it a good time to discuss Pluto’s role in the dwarf planet controversy. Those of us of a certain age were brought up on a simple view of the Solar System: the Sun, the nine planets (Mercury through Pluto), a collection of moons around most of the planets, the asteroid belt (I thought of this as interplanetary gravel between Mars and Jupiter) and a bunch of comets intermittently being drawn in from the not terribly specific depths of space.…

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