The US space agency’s New Horizons probe has made contact with Earth to confirm its successful flyby of the icy world known as Ultima Thule.
The encounter occurred some 6.5bn km (4bn miles) away, making it the most distant ever exploration of an object in our Solar System.
New Horizons acquired gigabytes of photos and other observations during the pass.
It will now send these home over the coming months.
The radio message from the robotic craft was picked up by one of Nasa’s big antennas, in Madrid, Spain.
It had taken fully six hours and eight minutes to traverse the great expanse of space between Ultima and Earth.
Controllers at the Johns Hopkins University Applied Physics Laboratory in Maryland greeted the reception of the signal with cheers and applause.
“We have a healthy spacecraft,” announced Mission Operations Manager Alice Bowman. “We’ve just accomplished the most distant flyby.”
This first radio message contained only engineering information on the status of the spacecraft, but it included confirmation that New Horizons executed its autonomous flyby observations as instructed and that the probe’s onboard memory was full.
A later downlink on Tuesday will see some choice images returned to give scientists and the public a taster of what New Horizons saw through its cameras.
If there is one note of caution it is that the timing and orientation of the spacecraft had to be spot on if the probe was not to shoot pictures of empty space! As a result, there’ll continue to be some anxiety until the data can be examined.
“The highest resolution images taken at closest approach required perfect pointing, almost,” said Project Scientist Hal Weaver. “We think, based on everything we’ve seen so far, that was achieved.”
Ultima is in what’s termed the Kuiper belt – the band of frozen material that orbits the Sun more than 2 billion km further out than the eighth of the classical planets, Neptune; and 1.5 billion km beyond even the dwarf planet Pluto which New Horizons visited in 2015.
It’s estimated there are hundreds of thousands of Kuiper members like Ultima, and their frigid state almost certainly holds clues to the formation conditions of the Solar System 4.6 billion years ago.
The vast separation between New Horizons and Earth, coupled with the probe’s small, 15-watt transmitter, mean data rates are glacial, however.
They top out at 1 kilobit per second. To retrieve all of the imagery stored on the probe is therefore expected to take until September 2020.