Pluto mission has a complication: We don't know exactly where the planet is

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Some 4.7 billion kilometres from Earth, the New Horizons spacecraft is heading for a historic rendezvous with Pluto. To achieve this, it will need to hit a very small target: an imaginary rectangle in space measuring just 100 by 150 kilometres.

Mission navigators need to put New Horizons precisely in that area to ensure that the spacecraft can make all planned science observations during its 14 July fly-by of Pluto — the first ever of that distant dwarf planet.

For now, the spacecraft is on target. But getting to Pluto is one of the hardest tasks in interplanetary navigation, and crucial decisions will be made in the next week and a half. The last chance to change the spacecraft’s flight path comes on 4 July.

Because astronomers discovered the dwarf planet in 1930, they have seen only part of its 248-year path around the Sun, and they don’t know exactly where Pluto is. And New Horizons is so far from Earth that it takes 9 hours to send and receive a signal, making the spacecraft hard to direct in real time.

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