The fastest man-made object ever built, the Pluto-bound New Horizons probe, is now closer to the former planet than Earth, just a little under four years after its launch.

It's currently traveling at about 31,000 miles an hour and is located about 1.527 billion miles from Earth.

"Today, 29 Dec 2009, New Horizons crossed a milestone boundary– henceforth we're now closer to Pluto than to Earth. Go New Horizons!" the mission's controllers tweeted Tuesday.

The spacecraft will be the first to fly by Pluto, the planet or dwarf planet or plutoid, and on to the other objects lurking in the Kuiper Belt at the edge of the solar system.

While the craft is hibernating most of the time while it awaits its July 2015 rendezvous with Pluto, it was roused for a Jupiter flyby that yielded some gorgeously detailed images of that planet and its satellites.

Unlike an orbiter, much of the New Horizons activity will come in an action-packed nine day period around July 14, 2015 when the craft approaches and then passes by Pluto. During that time, the probe will capture 4.5 gigabytes of data, which it will keep sending on the four-and-a-half-hour trip back home for months.

With its main mission accomplished, the craft will continue moving away from the sun, following in the extrasolar footsteps of the earlier Pioneer and Voyager missions, drifting ever farther away from us.

Instead of the plaques attached to the earlier ships, which presumably identify the spacecraft as artifacts of Earthly civilization, New Horizons carries a DVD inscribed with 450,000 names of supporters and some of the ashes of Clyde Tombaugh, who discovered Pluto in 1930.

Images: NASA

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