Nasa completes tour of solar system with a fly-by of Pluto
Pluto was unofficially upgraded yesterday as Nasa announced it had completed its mission to visit every planet in the Solar System.
Although the icy world was demoted to a dwarf planet in 2006, the head of the American space agency, Charles Bolden, said that he still viewed Pluto as a full planet and claimed the 'fly-by' by the New Horizons spacecraft marked the end of a task started by Nasa when John F. Kennedy was president.
New Horizons made its closest approach to Pluto at 12.49pm yesterday afternoon, speeding over the surface at a height of 7,750 miles.
The first close-up images are expected to be released at around 8pm this evening.
At the Applied Physics Laboratory (APL) at Johns Hopkins University in Maryland, mission control staff and visitors clapped, cheered and waved American flags, chanting 'USA, USA' in an outpouring of patriotic emotion.
"It's a big day for Nasa," said Mr Bolden. "The US today has become the first nation to visit every planet. We're calling Pluto a planet - technically, it's a dwarf planet. I call it a planet, but I'm not the rule-maker.
"We wanted to demonstrate that we could navigate the last known planet in our Solar System. That is an incredible technological achievement."
Measurements sent back by New Horizons as it came close to Pluto showed that the dwarf planet was 20-30km larger than previously thought, with a radius of 1,184km. Significantly, it makes it larger than Eris, a body discovered in 2005. The fact that Pluto was smaller than Eris was one of the strongest arguments for reclassifying Pluto as a minor planet in 2006.
"Maybe we need to reconsider its status again," said Dr Daniel Brown, an astronomy expert at Nottingham Trent University. Even without full planet status, Pluto still has many secrets to give up.
Intriguingly, it appears the dwarf planet is red, a result of the chemical action of sunlight generating red compounds in the atmosphere that then fall on the surface.
New Horizon's principal investigator, Dr Alan Stern, promised a "16-month data waterfall" ahead that will help scientists re-write the textbooks about Pluto.
A stunning new image of Pluto was also posted by Nasa on Instagram, taken from a distance of 766,000km. It clearly shows the dwarf planet's surprising Mars-like reddish hue, and the enigmatic heart-shaped feature on its surface. Other photos taken from a million kilometres away revealed evidence of cliffs, craters and chasms larger than the Grand Canyon.
Speaking at APL, former astronaut John Grunsfeld, associate administrator of Nasa's Science Mission Directorate, said: "It's just amazing. This is truly a landmark in human history. People often think the success of missions like this is about engineers, the hardware, but the real key is teamwork, and that's what Nasa excels at.
New Horizons has taken more than nine years to reach Pluto, carrying with it the ashes of astronomer Clyde Tombaugh - who discovered the remote icy object in 1930.
Brendan Owens, from the Greenwich Royal Observatory in London, said: "The images of Pluto we got previously have been only a few pixels across, just showing areas of light and dark on this world.
"Now we're getting up close and personal, something that has never been done before. This whole region is hard for astronomers to explore because we rely on light, and at that distance so little sunlight falls on these objects you have very little data to work with."
The arrival of New Horizons at Pluto will be remembered as the beginning of the exploration of 'The Third Zone', also known as the mysterious Kuiper Belt, a huge band of planetary debris left over from the solar system's formation 4.56 billion years ago.
"Over the next 20 years it could return scientific data from a Kuiper Belt fly-by and we have a chance to go further to potentially sample interstellar space," said Dr Stern. (© Daily Telegraph, London)