In 1930, the Lowell Observatory in Arizona announced the discovery of a small, odd world, roaming beyond the known planets in a region barely visible through the most powerful telescopes.
Seventy-five years later that historic find – Pluto – remains almost as much of a mystery as it was then. No spacecraft has ever visited it, and not even the Hubble Telescope can spot details on its rocky, icy surface.
Yet with the New Horizons mission, NASA looks to unlock one of the solar system's last, great planetary secrets.
"The United States has made history by being the only nation to reach every planet from Mercury to Neptune with a space probe," said New Horizons principal investigator Alan Stern, of the Southwest Research Institute, Boulder, Colo. "With New Horizons, the U.S. can complete the reconnaissance of the solar system and round out our knowledge of the planets."
New Horizons will cross the span of the solar system – in record time – and conduct flyby studies of Pluto and its moon, Charon, in 2015. The seven science instruments on the piano-sized probe will shed light on the bodies' surface properties, geology, interior makeup and atmospheres.
It will mark humankind's first voyage into the "third zone" of the solar system known as the Kuiper Belt, populated by smaller, icy objects different than the rocky inner planets or the outer gas giants.