CAPE CANAVERAL, Florida (AP) — A piano-sized spacecraft blasted off Thursday on a 3-billion mile journey to study Pluto, the solar system’s last unexplored planet, and examine a mysterious zone of icy objects at the outer edges of the planetary system.

The New Horizons probe lifted off from the Cape Canaveral Air Force Station at 2 p.m., quickly reaching speeds of 36,000 mph as it pushed away from Earth.

It was the swiftest spacecraft ever launched and is expected to reach the moon in nine hours and Jupiter in just over a year.

The distance involved means scientists won’t be able to receive data on Pluto until at least July 2015.

The launch drew attention from opponents of nuclear power because the spacecraft is powered by 24 pounds of plutonium, whose natural radioactive decay will generate electricity for the probe’s instruments.

NASA and the Department of Energy had estimated the probability of a launch accident that could release plutonium. As a precaution, the agencies brought in 16 mobile field teams that can detect radiation and 33 air samplers and monitors.

After two delays — first because of strong winds Tuesday at the launch pad, and then because of a power outage Wednesday at the spacecraft’s control center in Maryland — New Horizons got off the ground.

A successful journey to Pluto would complete an exploration of the planets started by NASA in the early 1960s with unmanned missions to observe Mars, Mercury and Venus.