This morning, 9.5 years and 3 billion miles after launching from Earth, the New Horizons spacecraft will zip past Pluto, coming within 7800 miles of the dwarf planet (closer than any of its five moons). Having departed Earth in January, 2006, New Horizons swung past Jupiter in February, 2007, gaining momentum and refining its course in the process.
Today, as it flashes past Pluto and its largest moon Charon, the spacecraft will be traveling at 31,000 miles per hour but will retrieve photos and scientific data never before available to human beings; this evening, that data will be transmitted to Earth, completing the primary goals of this amazing space mission. Already, we have learned that Pluto is greater than 1470 miles in diameter, larger than previously thought, and that it harbors a polar cap of frozen methane.
After collecting data on Pluto and its largest moon, New Horizons will travel through the Kuiper Belt on its way to the edge of our solar system and beyond. Aboard are the ashes of Clyde Tombaugh, the astronomer who discovered Pluto in 1930 (at the age of 24); of course, his partial remains will be the first human material to leave the solar system that gave birth to our species (some 4.9998 billion years after its formation).
Correction: the flyby distance was incorrect when first posted and has been changed
Correction 2: I clearly had a bad math day. Time from solar system formation to human evolution has been corrected