Every (traditional) planet in the solar system has been explored up-close -- except one, Pluto. That's about to change: tomorrow, the launch window for the New Horizons probe opens, and very soon (possibly by 1:24pm EST) the spacecraft will be off on its 15 year mission to Pluto and beyond.

The NASA Press Kit for the New Horizons probe (PDF) provides a terrific overview of the mission, the space craft, and what scientists hope to learn when it finally gets to Pluto in 2015 -- and the Kuiper Belt in 2020.

The craft will map the surfaces of Pluto and Charon with an average resolution of one kilometer (in contrast, the Hubble Space Telescope cannot do better than about 500- kilometer resolution when it views Pluto and Charon). It will map the surface composition across the various geological provinces of the two bodies. And it will determine the composition, structure and escape rate of Pluto’s atmosphere.

New Horizons will be the fastest space craft ever built by humankind, traveling at 16 kilometers per second (or around 30,000 miles per hour) -- and it will still take over 9 years to get to Pluto.