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Five years of flight for Pluto probe

Five years ago today, NASA launched the New Horizons probe on the fastest rocket ever to leave Earth, beginning a journey to the farthest world ever targeted by a space mission. Back then, Pluto was considered the only one of the nine planets not yet explored. Today, it's widely accepted that Pluto is part of a troop of dwarf planets. There may be several other worlds like Pluto out there on the solar system's dark, cold frontier. There may be hundreds of them. New Horizons may well shed new light on that mystery, and many others, when it passes by Pluto in 2015.

New Horizons' Twitter account is positively chirping with birthday updates today: The 9-foot-wide probe is currently about 1.85 billion miles from Earth, and more than halfway to Pluto. Along the way, the spacecraft's camera has caught sight of Jupiter, Uranus, Neptune and Pluto as well as the dwarf planets Makemake and Haumea. It's so close to its prescribed path that no course corrections will be required this year. The mission team is already planning the timeline for the 2015 approach, as well as an extended mission in the solar system's icy Kuiper Belt that could go all the way out to 2040.

It's no secret that Pluto is one of my favorite worlds, partly because of the controversy that's been bubbling around the dwarf planet for the past five years. I delve into that controversy in my book, "The Case for Pluto." You can easily guess where I stand on the planet-vs.-non-planet issue — but no matter where you stand, today's a great day to raise a toast to the scientists and engineers behind New Horizons. Preferably with Planet Pluto wine.

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