Kuiper Belt Missions Could Reveal the Solar System’s Origins

Michael D. Lemonick at Scientific American

"Just a bit more than 20 years ago, in fact, nobody even knew that the Kuiper belt existed. Since then, planetary scientists have discovered a handful of frozen worlds that approach and even rival Pluto in size. They have seen evidence that points to a long-ago violent reshuffling of the orbits of Jupiter, Saturn, Uranus and Neptune—and maybe even to the existence of a lost fifth giant planet. They have analyzed the sizes and orbits of the 1,500 or so known Kuiper belt objects (KBOs) to get a handle on how the belt itself took shape—wondering whether crashing icefalls from the nascent Kuiper belt once bestowed oceans on a young, dry Earth."