A NASA spacecraft's epic Pluto encounter is officially underway.

NASA's New Horizons probe today (Jan. 15) began its six-month approach to Pluto, which will culminate with the first-ever close flyby of the dwarf planet on July 14.

"We really are on Pluto's doorstep," New Horizons principal investigator Alan Stern said last month during a news conference at the annual fall meeting of the American Geophysical Union (AGU) in San Francisco. [Photos from NASA's New Horizons Pluto Probe]

The $700 million New Horizons mission blasted off in January 2006 with the aim of lifting the veil on Pluto. The dwarf planet has remained a mystery since its 1930 discovery because it's so small and so far away. (On average, Pluto orbits about 40 times farther from the sun than Earth does.)

The piano-size spacecraft rocketed away from Earth at more than 36,000 mph (58,000 km/h), faster than any other probe. It has now covered about 3 billion miles (4.8 billion kilometers) during its nine-year journey through deep space.

"In a very real sense, this is the Everest of planetary exploration," Stern said of New Horizons. "This mission represents the closing of the first era of planetary reconnaissance. We've made it to the farthest place, with the fastest spacecraft ever launched."

New Horizons will use seven different science instruments to study Pluto and its five known moons. The mission's chief objectives include mapping the surface composition and temperature of Pluto and its largest moon, Charon; characterizing the atmosphere of Pluto and the geology of Pluto and Charon; and hunting for rings and additional satellites in the Pluto system.

In the 1990s, researchers began to realize that Pluto is not a lonely misfit; rather, it's just one of many dwarf planets and other icy denizens of the far-flung Kuiper Belt, which lies beyond Neptune's orbit. So New Horizons' observations should help researchers better understand an entire class of solar system bodies, mission team members said.

"We are going to the archetypal Kuiper Belt planet," New Horizons co-investigator William McKinnon, of Washington University in St. Louis, said at the AGU news briefing. "This mission will revolutionize our understanding of how the planets in the Kuiper Belt work."

Small, icy worlds like Pluto are probably the most common type of planet in the entire universe, McKinnon added.

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NASA Pluto Probe Begins Science Observations Ahead of Epic Flyby