The discovery of Pluto's fifth moon puts the distant world into a category all of its own
The discovery of a fifth moon orbiting Pluto has stirred up fresh complaints about its demotion from the ranks of fully fledged planets. Six years after the International Astronomical Union ruling, is it time for a rethink?
Maybe. A few decades ago, the difference between planets and lesser bodies such as asteroids and moons seemed clear. The more we learn about the solar system, the harder it gets to classify its various bodies into distinct categories.
We now know that Pluto and its relatively huge moon Charon form a binary pair orbiting a common point between them, with at least four smaller bodies in neat orbits around them (see "Discovery of fifth moon reignites Pluto planet debate").
As far as we know, there's nothing else quite like it in the solar system. Neither "planet" nor "dwarf planet" seem to do it justice. Perhaps Pluto/Charon deserves a category all of its own.To read more, click here.