NASA calls it a cosmic coincidence.
On Monday, NASA's New Horizons spacecraft crossed the orbit of Neptune on its way to Pluto. The celestial milestone occurred on the 25th anniversary of Voyager 2's historic flyby of Neptune.
It's the last major intersection for New Horizons, which is due at Pluto next summer after nearly a decade of travel.
Neptune wasn't exactly close to the spacecraft Monday. In fact, the planet was 2.5 billion miles (4 billion kilometers) away.
Scientist Alan Stern of the Southwest Research Institute in Boulder, Colorado, says this will be the first opportunity in a generation to explore a new planetary system up close. New Horizons will study not only mysterious Pluto, but also its moons, some of which might still be hidden.
Explore further: Voyager map details Neptune's strange moon Triton