Pluto: We’re Finally Getting A Good Look at Pluto, New Horizons, the fastest spacecraft ever flown, made history as it shot past Pluto at more than 30,000mph taking pictures and collecting scientific data.
During the fly-by, the first close encounter with Pluto ever achieved, the American probe passed within 12,500 kilometres (7,767 miles) of the mysterious world.
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.
The spacecraft was due to make its closest approach to Pluto at 12.49pm UK time.
All the indications are that the fly-by has been a success, but the New Horizons team will not know for sure until the probe contacts Earth again at 01.53 UK time tomorrow.
Earlier the American space agency Nasa posted a stunning new image of Pluto on Instagram, taken by New Horizons from a distance of 476,000 miles.
It clearly shows the dwarf planet’s surprising Mars-like reddish hue, and the enigmatic heart-shaped feature on its surface that has already become Pluto’s calling card on the internet.
Other photos taken from a million miles away revealed evidence of cliffs, craters and chasms larger than the Earth’s 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 team work, and that’s what Nasa excels at.
“We’re celebrating the moment New Horizons had its closest approach to Pluto, but we’re not talking to the spacecraft; it’s doing its job. Tonight we’re going to get the signal, the ping, (telling us) that it made it through the system and it’s ready to start sending us a treasure trove of data.”
New Horizons has taken more than nine years to reach Pluto, carrying with it the ashes of the astronomer who discovered the remote icy object in 1930.
When the mission was launched in January 2006, the aim was to reach the outermost of the Sun’s family of nine planets. Seven months into the probe’s epic journey, international astronomers downgraded Pluto’s status to “dwarf planet”.
But despite its small size – just over two-thirds the diameter of the Earth’s moon – Pluto looks and behaves like a fully fledged planet, having an atmosphere and no less than five moons of its own.
Currently, Pluto is just under three billion miles from Earth, one of a number of distant “worldlets” in a region known as the Kuiper Belt.
It is so far away that its light takes more than four hours to reach the Earth, making communication with New Horizons an exercise in patience.
New Horizons has already answered one basic question about Pluto, its precise size. Scientists used photos from the spacecraft’s telescopic camera, the Long Range Reconnaissance Imager (Lorri), to determine that the dwarf planet is somewhat larger than previously thought, having a diameter of 1,473 miles.
The result confirms that Pluto is larger than any other known solar system object beyond the orbit of Neptune.
Mission scientist Dr Bill McKinnon, from the University of Washington, said: “The size of Pluto has been debated since its discovery in 1930. We are excited to finally lay this question to rest.”
The dwarf planet’s unusual colour has also enthralled scientists. Far from being a drab grey, as expected, it turns out to be salmon red.
Experts believe the colour arises from the chemical action of sunlight generating red compounds in the atmosphere that then fall on the surface.
Speaking earlier on Nasa TV, the space agency’s administrator Charles Bolden – who insisted on giving Pluto its old title of planet – said: “I’m fascinated personally by the colour of the planet. I expected to see a cold, grey planet on the edge of the solar system, but we see a planet with this reddish tint not unlike Mars.”
Describing the technical achievement of arriving at such a tiny target so far away, he said: “It’s like hitting a golf ball from Capitol Hill and making a hole in one on the west coast of the United States, intentionally.”
Close up images taken by New Horizons are expected to show surface features just 50 metres (164ft) across.
The 700 million dollar (£451 million) probe, the size of a baby grand piano, has journeyed a total of three billion miles to reach Pluto, which is currently about that distance from Earth.
After launching on January 19 2006, it reached an Earth-relative velocity of 36,373mph, making it the fastest space vehicle in history.
British astronomer Brendan Owens, from the Greenwich Royal Observatory in London, said: “This is really unexplored territory. 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 that you have very little data to work with.”
“Learning about the composition of Pluto may give us more of a handle on the make-up of the solar system.”
The mission marks the conclusion of Nasa’s quest to explore every planet in the solar system, starting with Venus in 1962.
Today’s encounter with Pluto coincides with the 50th anniversary of the first ever fly-by of Mars by the Mariner 4 probe.
The mission’s principal scientist Alan Stern told the Associated Press news agency: “We’re going to knock your socks off.
“What Nasa’s doing with New Horizons is unprecedented in our time … the last picture show for a very, very long time.”
Pluto has a thin atmosphere of nitrogen, methane and carbon dioxide, which expands as the dwarf planet’s elongated 248-year orbit takes it closer to the Sun, causing icy material on its surface to vaporise.
Since its discovery, only a third of Pluto’s year – the time it takes to complete one orbit of the Sun – has passed.
Scientists believe the dwarf planet may bear signs of past volcanic activity and could even have liquid water beneath its frozen surface.
New Horizons team member Professor Bill McKinnon, from Washington University in St Louis, said: “I’m really hoping to see a very active and dynamic world.”
The spacecraft is also looking at Pluto’s giant moon Charon, which is just over half its size, as well as its other moons Styx, Nix, Hydra and Kerberos.
Besides its telescopic camera, the probe also carries a suite of sophisticated instruments for analysing Pluto’s composition and studying its atmosphere.
Pluto was identified in 1930 by US astronomer Clyde Tombaugh using a 13in photographic telescope at the Lowell Observatory in Flagstaff, Arizona.
Some of his ashes are being carried to the world he discovered on New Horizons.
Because of the probe’s great distance from Earth and the slow speed of data transmission, it will take many months to process information from the mission.