Why Are Planets Round?
When they tried to figure out how to define a planet, one of the criteria that astronomers settled on was whether its body was spherical, instead of irregular. Indeed, the fact that Pluto is spherical is one of the reasons the category of "dwarf planet" was created when it was downgraded from a fully fledged planet because its shape meant it was still too planet-like to be called anything else.
But what is it that makes planets round? Why are they that shape and not something else?