NASA's New Horizons spacecraft came out of hibernation this weekend after nine years and three billion miles of travel for its encounter with the Pluto system.

The NASA spacecraft has gone further than any space mission has ever gone in order to arrive at its primary target. The probe was switched into active mode in order to prep for the exploration of Pluto and its moons sometime in 2015.

"This is a watershed event that signals the end of New Horizons crossing of a vast ocean of space to the very frontier of our solar system," said Alan Stern, New Horizons principal investigator from Southwest Research Institute, according to a company release.

New Horizon launched back on January 19, 2006. It is now approaching Pluto and is expected to start its encounter there in 2015. Over the next several weeks, NASA will spend its time checking the spacecraft's systems.

New Horizons has spent 1,873 days, or about two-thirds of its flight time, in hibernation. From mid-2007 to late 2014, its 18 separate hibernation periods ranged from 36 days to 202 days.

The team put the craft into hibernation in order to save "wear and tear on spacecraft components" and reduce the risk of system failures.

"Technically, this was routine, since the wake-up was a procedure that we'd done many times before," said Glen Fountain, New Horizons project manager at APL, according to the space agency. "Symbolically, however, this is a big deal. It means the start of our pre-encounter operations."

New Horizons will start observing the Pluto system on Jan. 15. 

New Horizons' closest approach to Pluto will take place on July 14, though plenty of highlights are expected before then.

"New Horizons is on a journey to a new class of planets we've never seen, in a place we've never been before," says New Horizons Project Scientist Hal Weaver, of APL, according to the release. "For decades we thought Pluto was this odd little body on the planetary outskirts; now we know it's really a gateway to an entire region of new worlds in the Kuiper Belt, and New Horizons is going to provide the first close-up look at them."

Considering that Pluto is in our solar system, scientists currently know very little about it. It was first spotted back in 1930, but it took until the 1990s for astronomers to realize that it wasn't alone in its distant orbit.

Pluto is part of a complex system of 1,000 bodies called the Kuiper belt. Still to this day, experts from all over the world are torn on whether Pluto can be called a planet.

"The geophysical definition of a planet is that the object has enough mass that its gravity holds it in a perfect sphere," said Harold Weaver, of Johns Hopkins and the principal project scientist on the mission, according to the release. "Pluto is almost a perfect sphere, and on this mission we will find out if has enough mass that it deserves to be in the planet category."

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