The world has been abuzz with news of Rosetta’s arrival at its comet target recently, with the mission making headlines across the globe.

But next year on 14 July 2015 an even more remarkable mission will reach its climax - Nasa’s New Horizons probe will flyby Pluto in the culmination of a nine-year journey, returning the first ever close-up images of the dwarf planet.

And Nasa has announced that the spacecraft has now crossed the orbit of Neptune, the last planetary crossing on its way to Pluto, in record time.

The New Horizons probe (artist's illustration shown) has passed the orbit of Neptune on its way to Pluto. Officials at Nasa in Washington DC heralded the milestone as a key moment for the mission. This was the largest major planetary crossing before the spacecraft arrives at Pluto on 14 July 2015

The piano-sized spacecraft, which launched in January 2006, reached Neptune’s orbit in just eight years and eight months.

TIMELINE OF THE NEW HORIZONS MISSION 8 June 2001 New Horizons is selected as a mission by Nasa 19 January 2006 The spacecraft successfully launches at a speed of 36,373 mph (58,536 km/h) - the fastest spacecraft ever to leave Earth orbit, 100 times faster than a jetliner. 7 April 2006 The spacecraft passes the orbit of Mars 28 February 2007 New Horizons flies by Jupiter at a distance of 1.43 million miles (2.31 million km). 8 June 2008 The probe passes Saturn’s orbit. 25 February 2010 New Horizons reaches the halfway point in its more than 3 billion-mile (4.8 billion km) journey to Pluto. 18 March 2011 The spacecraft passes the orbit of Uranus. 25 August 2014 Yesterday’s milestone saw the spacecraft pass the orbit of Neptune. 14 July 2015 New Horizons’ flyby of Pluto begins. Extensive images and readings will be taken before and after, including mapping of the surface of Pluto and its moon Charon to a resolution of 25 miles (40 km). 2016-2020 New Horizons will flyby one or several Kuiper Belt Objects (KBOs), if any suitable candidates can be found. 2026 The mission formally ends. 2038 If still operational, the probe will explore the outer reaches of the sun’s influence on the solar system - the heliosphere. Advertisement

That beats the previous time to travel this distance of nearly 2.75 billion miles (4.4 billion km) taken by Voyager 2 by nearly four years.

And in a rather fitting tribute to its predecessor, the milestone comes on the 25th anniversary of Voyager 2’s encounter with Neptune on 25 August 1989.

‘It's a cosmic coincidence that connects one of Nasa’s iconic past outer solar system explorers, with our next outer solar system explorer,’ said Dr Jim Green, director of Nasa’s Planetary Science Division at Nasa Headquarters in Washington.

‘Exactly 25 years ago at Neptune, Voyager 2 delivered our “first” look at an unexplored planet.

‘Now it will be New Horizons' turn to reveal the unexplored Pluto and its moons in stunning detail next summer on its way into the vast outer reaches of the solar system.’

While New Horizons is crossing the orbital path of Neptune, the mission was not designed to encounter the planet - instead, Pluto is the primary target of the mission.

In fact, Neptune is actually 2.48 billion miles (4 billion km) from New Horizons at this moment, and with the spacecraft heading out of the solar system it will never encounter the gas giant.

Nonetheless the milestone is important - it marks a key stage of the mission and the last ‘hurdle’, with all the major planets now crossed ahead of the rendezvous with Pluto next year.

New Horizons' journey is so long that when it first launched on 19 January 2006 Pluto was still classified as the ninth planet of the solar system.

It was controversially reclassified as a dwarf planet in August 2006 when another body, Eris, was found to be larger.

This led to the International Astronomical Union (IAU) redefining what it means to be a planet, and in the third category Pluto fell short - namely, it had not cleared the neighbourhood around its orbit.

But whatever its designation, the mission is of huge importance.

Barring a few blurry images from Hubble and other long-distance images, no human has ever truly seen what Pluto looks like.

Although Neptune (pictured by Voyager 2 in 1989) was nowhere near at the time, the crossing of its orbit is still an important moment in the New Horizons mission. It also came on the 25th anniversary of Voyager 2's first look at the gas giant back in 1989

This diagram shows New Horizons' position now. For reference, 1 AU (astronomical unit) is defined as the distance from Earth to the sun. The diagram also shows how it takes more than eight house to communicate with the spacecraft as it is so far away

Just like Voyager 2’s visit to Uranus and Neptune, which returned the first ever images of those worlds, New Horizons’ discoveries promise to be just as groundbreaking.

THE PLUTO SYSTEM Pluto is an extremely distant world, orbiting the sun more than 29 times farther than Earth. It is about two thirds the size of our moon. With a surface temperature estimated to be -229°C (-380°F), the environment at Pluto is far too cold to allow liquid water on its surface. Pluto's moons are also in the same frigid environment. The moon Charon is almost half the size of Pluto. The moon is so big that Pluto and Charon are sometimes referred to as a double dwarf planet system. The distance between them is 12,200 miles (19,640 km). Charon's orbit around Pluto takes 6.4 Earth days. Charon neither rises nor sets, but hovers over the same spot on Pluto's surface. The same side of Charon always faces Pluto - this is called tidal locking. Compared with most of the planets and moons, the Pluto-Charon system is tipped on its side. Advertisement

What Pluto looks like is still unknown, with some estimating it might have a vast icy surface, possibly even with a cloudy atmosphere, while others say it will be more barren like Neptune’s moon Triton.

‘Nasa’s Voyager 1 and 2 explored the entire middle zone of the solar system where the giant planets orbit,’ said Dr Alan Stern, New Horizons principal investigator at the Southwest Research Institute in Boulder, Colorado.

‘Now we stand on Voyager's broad shoulders to explore the even more distant and mysterious Pluto system.’

Like Voyager 1 and 2 before it, New Horizons is also on a path towards the Kuiper Belt after it has flown by Pluto.

The Kuiper Belt is a disc-shaped region of icy objects past the orbit of Neptune, but it still remains somewhat of a mystery.

In fact Nasa had been concerned that rogue Kuiper Belt objects could pose a threat to New Horizons if it encountered one on the way.

In addition, while Pluto is the main goal, officials had been hoping to find a suitable target in the Kuiper Belt the spacecraft could visit.

However, none has yet been find - and it will be a race against time to find one before the spacecraft leaves the vicinity of Pluto next year.

This image taken by the Hubble Space Telescope in 2012 shows Pluto and its five moons. Styx, also known as P5, is the most recently discovered. The main targets for the New Horizons mission will be Pluto and its largest moon Charon, with the spacecraft planning to map the surface of the to a resolution of 25 miles (40 km)