I kind of love how Pluto is an 'alien' to our solar system, having come from somewhere else and gotten snagged by our sun's gravity.
It might be fun for a Legion story to reveal how Pluto is not a moon or planetoid, but actually the larval stage of some vast creature, and the team has to assemble to get it out of our solar system when it finally awakens and starts moving to devour settlements and space stations around Neptune, etc.
Of course, even after they do so, our solar systems gravity has had a long time to 'get used' to having Pluto in the mix, so they then have to assemble a new Pluto out of debris from the Oort cloud, so that, to a casual observer, our solar system looks the same as it did before 'Pluto' woke up and tried to eat us...