The New Horizons mission has been launched to Pluto. It is the first time a spacecraft has been sent to an unexplored world since the Voyager 2 craft visited Neptune in the late 1980s.
New Horizons' trip to Pluto and the Kuiper Belt Objects will cover uncharted territory in the exploration of the Solar System.
The billions of kilometres New Horizons must cross to reach Pluto means it will not arrive until July 2015.
And even to achieve that, Nasa must put the probe in a "slingshot" around Jupiter, using the giant planet's gravity to throw New Horizons towards the outer reaches of the Solar System at speeds of 25km/s (56,000mph).
Nasa considers reaching Pluto part of its "historic endeavour" of space exploration and New Horizons a chance to "understand worlds at the edge of our Solar System".
Pluto and its moon, Charon, form what could be described as a "double world" or binary - an arrangement that is thought to be common, but which has not been studied in detail before.
It will also be the first time that one of the dwarf planets and the hundreds of Kuiper Belt Objects beyond Neptune's orbit have been visited.
Click here to see New Horizons' route to Pluto
New Horizons was launched aboard a powerful Atlas V rocket from Cape Canaveral, Florida, on 19 January, 2006.
It will spend the first 13 months heading towards Jupiter, with key checks taking place.
The spacecraft's closest encounter with Jupiter will take place between 25 February and 2 March 2007, offering new chances to map the surface and atmosphere of its moons.
For the next eight years, New Horizons will cruise towards Pluto, being "woken" annually for technical checks and rehearsals for its encounter with the distant world.
Long before it approaches Pluto, New Horizons will start collecting data. The first maps of Pluto and Charon will be made three months before the period of closest approach.
During the day-long fly-by, ultraviolet emissions from Pluto's atmosphere will be measured and the best quality maps of Pluto and Charon, including surface detail, will be made.
At the closest point, New Horizons will be 10,000km (6,200 miles) from Pluto and about 27,000km (16,800 miles) from Charon.
The probe will then look back at the "dark side" of the binary to spot haze, look for rings and examine the objects' surfaces.
Even then, the $650m (£368m) mission may not be over; with Nasa approval it will travel on to an as yet undecided Kuiper Belt Objects for further studies.
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