The scientists running NASA's New Horizons mission showed off the first detailed images Wednesday of an object 4 billion miles away in space.
The new images - taken from as close as 27 000km on approach - revealed Ultima Thule as a "contact binary", consisting of two connected spheres.
"What this spacecraft and this team accomplished is unprecedented", said Alan Stern, the mission's principal investigator, before unveiling the first images.
The picture came after flight controllers said they had had success in the high-risk, middle-of-the-night encounter at the mysterious body known as Ultima Thule on the frozen fringes of our solar system, an astounding 1 billion miles beyond Pluto.
This composite image made available by NASA shows the Kuiper Belt object nicknamed "Ultima Thule", indicated by the crosshairs at center, with stars surrounding it made by the New Horizons spacecraft, on August 16, 2018.
Scientists can also now infer some geological properties of Ultima Thule. Cathy Olkin, deputy project scientist, said the object has a rotation period of approximately 15 hours. "[This] has set a new bar for state-of-the-art spacecraft navigation".
Light travel time back to the Earth was expected to be some six hours as we await the images that will hopefully be coming in from this distant remnant of the creation of the solar system!
NASA's New Horizons, the spacecraft that dispatched back pictures of Pluto 3½ years ago, flounced the bygone peculiar matter early on New Year's Day.
The New Horizons team was also able to pin down Ultima Thule's size more accurately. Those images should reveal whether Ultima Thule has any rings or moons, or craters on its dark, reddish surface.
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Its mission now totaling $800 million, the baby grand piano-sized New Horizons will keep hurtling toward the edge of the solar system, observing Kuiper Belt Objects, or KBOs, from afar, and taking cosmic particle measurements.
It's a moment that could define the future, but the name "Ultima Thule" is one from the past.
The flyby took place about a billion miles beyond Pluto, which was until now the most faraway world ever visited up close by a spacecraft.
"I've said it a number of times, I think New Horizons is an example - one of the best examples in our time - of raw exploration, and the term Ultima Thule, which is very old, many centuries old, possibly over a thousand years old, is a wonderful meme for exploration", Stern said.
Planetary scientists have never before seen a close-up of a body like Ultima Thule.
Another possibility is Ultima could be two objects orbiting each other, researchers said. Unlike comets and other objects that have been altered by the sun over time, Ultima Thule is in its pure, original state: It's been in the deep-freeze Kuiper Belt on the fringes of our solar system from the beginning.
The images have been taken from as close as 17,000 miles, though it will take days for the high-resolution photos to be uploaded to Earth, given the bandwidth limitations of moving data across the span of the entire solar system.
He added: "It is going to revolutionise our knowledge of planetary science".
Clues about the surface composition of Ultima Thule should start rolling in by Thursday.