After nine-and-a-half years in space, Nasa’s spacecraft New Horizons soared past Pluto at 31,000mph (50,000km/h).
At least, that’s what the team hopes happened.
Confirmation of the flyby won’t be received until about 02:00 BST on Wednesday.
Until then, the craft will be too busy taking pictures and measurements – and it also takes more than four hours for the signals to beam back to Earth.
The probe was set to grab more images and other data as it passed just 12,500km from the little world at 11:50 GMT (12:50 BST).
The spacecraft is currently out of contact with Earth as it continues its observations.
But scientists already have colour data from the approach and said they might release another new picture of Pluto later on Tuesday.
Images set to be released on Wednesday will be more than 10 times the resolution of those already published.
New Horizons’ flyby of 2,370km-wide Pluto is a key moment in the history of space exploration.
It marks the fact that all nine objects considered by many to be the Solar System’s planets – from Mercury through to Pluto – have now been visited at least once by a probe.
“We have completed the initial reconnaissance of the Solar System, an endeavour started under President Kennedy more than 50 years ago and continuing to today under President Obama,” said the mission’s chief scientist, Alan Stern.
“It’s really historic what the US has done, and the New Horizons team is really proud to have been able to run that anchor leg and make this accomplishment.”
“This is true exploration… that view is just the first of many rewards the team will getJohn Grunsfeld, Nasa science chief
Talking about the main image of Pluto that was returned just before the flyby began, Nasa’s science chief, John Grunsfeld, said: “This is true exploration… that view is just the first of many rewards the team will get. Pluto is an extraordinarily complex and interesting world.”
The information that has been acquired in recent weeks on approach to the dwarf world will be as nothing to the huge number of observations captured during the flyby. But scientists have already been attempting to interpret the data and images so far.
Dr Stern said: “On the surface we see a history of impacts, we see a history of surface activity in terms of some features we might be able to interpret as tectonic – indicating internal activity on the planet at some point in its past, and maybe even in its present.
“This is clearly a world where geology and atmosphere – climatology – play a role. Pluto has strong atmospheric cycles. It snows on the surface. These snows sublimate – (and) go back into the atmosphere – every 248-year orbit.”
The team also released two stretched colour images, of Pluto and its main moon, Charon. The treatment allows scientists to discern more easily some of the differences at the surface of the bodies in terms of composition and processing.
New Horizons is investigating not only Pluto and Charon, but also the four smaller moons in the system: Styx, Nix, Kerberos and Hydra.
To achieve that, it has had to perform a furious set of manoeuvres during the flyby, pointing every which way in the sky to lock on to the different targets.
The cheering and jubilation are phenomenal. There’s a powerful sense of achievement at sending a robotic craft three billion miles to Pluto. But there’s also something much more instinctive: the thrill of witnessing and sharing a great moment of discovery.
