Technicians work on the the cargo carried by a rocket. for the New Horizons mission to the planet Pluto on Friday, November 4, 2005, at the Kennedy Space Center in Cape Canaveral, Florida. (Photo: John Raoux/AP Wide World)

December 20, 2005—The first spacecraft designed to visit Pluto headed to the launchpad this weekend. In less than a month, New Horizons will blast off from Cape Canaveral, Florida, on a historic journey to the edge of our solar system.

The piano-sized spacecraft will also check out Pluto's moon, Charon, as well as two other moons discovered only this year. New Horizons will sample Pluto's atmosphere, take its temperature, snap pictures, and then poke around the neighborhood.

The mission "takes us 4 billion miles away and 4 billion years back in time," said Alan Stern, the project's lead scientist. Pluto is so far from Earth that if you stood on its icy surface, the sun would look no bigger than a star in the clear black sky.

Pluto's Identity Crisis

Pluto was discovered 75 years ago and hailed as the solar system's ninth, and possibly final, planet. But recently, scientists have found several objects in Pluto's neighborhood that look suspiciously like Pluto. Two of them, Quaoar and Sedna, are more than half Pluto's size.

The discoveries have triggered a debate—what is a planet? What does Pluto, a chunk of ice and rock, have in common with Saturn, a gas giant more than 20 times larger? Both circle the sun, and both are round, but the similarities end there.

Because so little is known about Pluto, astronomers are excited about the New Horizons mission. "We're going to see things we've never dreamed of," said astronomer Marc Buie.

Astronomers will have to be patient. New Horizons isn't scheduled to reach Pluto until the year 2015.