After nine years and a journey of nearly 3-billion miles (4.8 billion km), NASA's Pluto-bound New Horizons robotic probe has awoken from its hibernation in preparation for a unprecedented flyby of Pluto and other celestial bodies in the Kuiper Belt.

Above: Artist's concept of the New Horizons spacecraft as it approaches Pluto and its largest moon, Charon, in July 2015. | Image Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute

At 3:00 PM ET on Saturday, a pre-set alarm clock roused New Horizons from its hibernation mode. Owing to the extreme distance, NASA received confirmation at 9:30 PM ET, some 6.5 hours later.

In about six weeks, on January 15, 2015, the spacecraft will begin its scientific observations of the dwarf planet Pluto and one or two of its Kuiper belt objects depending on which are in a better position to be explored.

New Horizons will make its closest approach to Pluto on July 14, 2015. The probe will not be stationed in orbit around the dwarf planet. Mission planners say there are two reasons for this:

The first is an engineering reason. To get to Pluto (which is 5 billion kilometers or 3 billion miles from Earth) in just 9.5 years, as New Horizons will, the spacecraft must travel very, very quickly. As a result, New Horizons will speed by Pluto at a velocity of about 43,000 kilometers per hour (27,000 miles per hour). To get into orbit, operators would have to reduce that speed by over 90%, which would require more than 1,000 times the fuel that New Horizons can carry.

The second reason is scientific: If we did stop to go into orbit, we wouldn't be able to go on to explore the Kuiper Belt!

The $700 million mission has the following objectives:

  • Map the surface composition of Pluto and Charon
  • Characterize geology and morphology ("the look") of Pluto and Charon
  • Characterize the neutral atmosphere of Pluto and its escape rate
  • Search for an atmosphere around Charon
  • Map surface temperatures on Pluto and Charon
  • Search for rings and additional satellites around Pluto
  • Conduct similar investigations of one or more Kuiper Belt Objects

The New Horizons spacecraft is roughly 8 feet (2.5 meters) across and weighs about 1,050 pounds (480 kilograms) — about half a ton. It's about the size and shape of a baby grand piano. It carries seven scientific instruments:

  • Alice: An ultraviolet spectrometer used for measuring gas composition
  • Ralph: An infrared spectrometer (LEISA) for mapping surface composition and a color optical imager (MVIC) for mapping surface structure and composition
  • REX: A radio experiment for measuring atmospheric composition and temperature
  • LORRI: An optical telescope that provides the highest resolution imaging of the surface
  • PEPSSI: A plasma-sensing instrument for measuring particles escaping from Pluto's atmosphere
  • SWAP A plasma-sensing instrument for measuring the properties of the solar wind at Pluto, Pluto's atmospheric escape rate, and for searching for a magnetosphere around Pluto. The "solar wind" is a stream of charged particles streaming away from the Sun at high speed.
  • SDC: An instrument used to measure dust impacts at the New Horizons spacecraft during its entire trajectory

This movie of Pluto and Charon was taken by New Horizons back in July:

What an amazing time for space exploration! Just a few weeks ago we were bouncing probes off a comet, and now, in addition to New Horizons, we can expect Dawn to arrive at Ceres.

Images: NASA/JPL/New Horizons.