Third launch day lucky for Pluto probe

NASA successfully launched its New Horizons spacecraft to icy Pluto, the solar system's last unexplored planet.

The unmanned probe, which is the size of a piano, will study Pluto and its moon Charon. It will also examine the mysterious zone of the solar system known as the Kuiper Belt, a region of icy, rocky objects that may provide clues on the origin of planets.

• INDEPTH: Destination Pluto

"We have ignition and liftoff of NASA's New Horizons spacecraft on a decade-long voyage to visit the planet Pluto and then beyond," NASA commentator Bruce Buckingham announced Thursday.

The launch from an Atlas 5 rocket at Cape Canaveral, Fla., was delayed about 45 minutes to wait for clouds to clear.

High winds at the launch site and a storm-related power failure at a Maryland lab managing the mission had prevented the liftoff earlier this week.

The successful launch was a relief for anti-nuclear activists who said an accident would scatter radioactive plutonium that fuels the probe.

Mission scientists won't start to receive data on Pluto until at least July 2015.

"We're realizing just how much there is to the deep, outer solar system," said Alan Stern, the mission's principal investigator. "I think it's exciting that textbooks have to be rewritten, over and over."

Despite the rocket's power, it will take at least 9.5 years for the 478-kilogram probe to complete its journey of five billion kilometres.

The fastest spacecraft launched from Earth will get to Jupiter in 13 months, where it will take advantage of the planet's gravity to boost its speed, cutting the length of the trip by five years.

The spacecraft is carrying some ashes of Clyde Tombaugh, an American who discovered Pluto in 1930.