Nasa’s New Horizons spacecraft has made the first visit to Pluto, speeding past at 14km per second.
Earlier, the space agency released the most detailed picture yet as it hurtled towards the dwarf planet on Tuesday.
The probe was set to grab more pictures and other data as it passed 12,500km from Pluto at 11:50 GMT.
Controllers got a last health status report before the robotic craft turned its antenna away from the Earth to concentrate on its target.
There will be a long, anxious wait for everyone involved with the mission before the spacecraft calls home again, because the signal will be coming from almost five billion kilometres away.
New Horizons’ flyby of 2,370km-wide Pluto is a key moment in the history of space exploration.
“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 is 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.”
It marks the fact that every body in that system – from Mercury through to Pluto – will have been visited at least once by a space probe.
“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,” said John Grunsfeld, Nasa’s science chief.
Dr Stern said: “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 – go back into the atmosphere – every 248-year orbit.”
The probe will investigate not only Pluto but also its five moons: Charon, Styx, Nix, Kerberos and Hydra.
The mission team will not celebrate until New Horizons contacts Earth again, which is scheduled to happen at 00:53 GMT today.
This communication will contain only engineering information on the status of the probe, but controllers should be able to tell very quickly whether the flyby sequence worked properly or not.
On Monday, the New Horizons team announced a new, more precise measurement of Pluto’s diameter at 2,370km. The probe sees the girth of Charon to be very similar to earlier estimates, at 1,208km.
