For the first time two spacecraft will soon make up-close studies of objects from the solar system’s Kuiper Belt, a mysterious region beyond Neptune’s orbit. There, billions of icy asteroids represent pristine examples of the raw building blocks of the solar system’s planets.

NASA’s New Horizons mission will visit the Kuiper Belt’s largest member, the dwarf planet Pluto, in 2015. The European Rosetta spacecraft, on the other hand, recently arrived in orbit around a comet that originated in the belt.