Neptune , the farthest of the planets, acts like a shepherd for the outer solar system, gravitationally scattering distant asteroids known as Kuiper Belt Objects (KBOs). Understanding Neptune's history gives important clues to how the rest of the solar system evolved to its present state. Neptune itself is unique—tilted 30 degrees on its side, it is host to a few unusual moons, including the Pluto-sized moon called Triton. Triton orbits Neptune backward, an indicator that it did not form around Neptune but was instead captured by Neptune's gravity after it formed elsewhere in the solar system. New observations coupled with simulations of Neptune's evolutionary history indicate that an oft-overlooked Neptunian moon called Nereid may reveal the planet's past.…