The “demoted” dwarf planet Pluto and its largest moon Charon make an unusual pair, and for decades, scientists have been discussing how the binary system—in which each mutually orbits the other—came to be.

Pluto and its largest moon Charon could have come together via a 10-hour “kiss-and-capture” encounter after a grazing collision

Unlike Earth, where the Moon orbits the planet, Pluto and Charon orbit each other, forming a binary system that is more similar to the Earth-moon system than any other moon in the solar system.