Nasa's New Horizons Probe Passes Neptune Orbit En-Route to Pluto

A new Nasa probe called New Horizons passed Neptune's orbit Monday, nearly 25 years after Voyager 2 spacecraft executed the first-ever flyby of faraway Neptune and its icy moon Triton.

It was a perfect time for the New Horizons team to pay tribute to Voyager 2.

"We stand on the shoulders of giants - giants like Voyager project scientist Ed Stone and his Voyager science team that pioneered how to do the exploration of the deep outer solar system," Alan Stern, principal investigator of New Horizons, told the media.

New Horizons is scheduled to pass through the Pluto system July 14, 2015.

The New Horizons probe took a photo of Neptune and its moon Triton - nearly 4 billion km away at the time.

"They are so far away they ate only points of light. We do not see the kinds of detail to make the discoveries that Voyager could. That is the power of going close," Stern said.

Astronomers are expecting surprising results when New Horizons reaches Pluto because very little is known about the dwarf planet.

It is so dim and far away that the best photos by Nasa's powerful Hubble Space Telescope show Pluto as a blur of pixels, space.com reported.

"Everything that we know about the Pluto system today could probably fit on one piece of paper," Stern added.

New Horizons will map the dwarf planet and its five known moons, determine the composition of Pluto's surface and atmosphere, search for undiscovered moons and a ring system.