For centuries, the planetary giants— Jupiter with its distinctive red spot and Saturn with its massive rings— have been the most glamorous of the planets, while the outer orbs— Uranus, Neptune, and Pluto— have been viewed, when they've been viewable at all, as dim, remote, drab, and mysterious stepsisters. Then 11 years ago Voyager 2, its mission to Jupiter and Saturn completed, was allowed to fly by and snap a few images of Neptune. What it eventually sent back to Earth changed everything. Neptune was literally seen in a new light, with images of a gorgeous blue orb with swirling white clouds that seemed, well, Earth-like. Three years later, the discovery of the Kuiper belt, a field of remote icy objects that includes Pluto, redefined Neptune as a major force in the arrangement of the entire solar system. Astronomers now believe Neptune's gravity not only skewed the orbits of the small, distant bodies in the Kuiper belt but also affected the position of the giant gas planets.
"No one planet can tell us everything about the universe," says Heidi Hammel, a senior scientist with the Space Science Institute in Boulder, Colorado, "but Neptune seems to hold more than its share of information about the formation of our own solar system— as well as the solar systems beyond."
