It’s a snowman, a bowling pin ... a world
NASA releases up-close, first images of distant Ultima Thule object
The most distant object ever explored by spacecraft is a reddish, snowman-shaped rock 4 billion miles from Earth.
The object, nicknamed Ultima Thule, was photographed by NASA’s New Horizons spacecraft during a late-night rendezvous on the first day of 2019.
It is the first inhabitant of the Kuiper belt — the ring of rocky relics surrounding the outer solar system — that scientists have seen up close.
Its odd shape, which scientists term a “contact binary,” indicates it formed as two spherical rocks slowly fused together in the early days of the solar system. This finding lends support to a theory of planet formation that suggests worlds are born from slow accumulation, rather than catastrophic collisions, researchers said.
“This is exactly what we need to move the modelling work on planetary formation forward,” said Cathy Olkin, the mission’s deputy project scientist. “Ultima is telling us about our evolutionary history.”
New Horizons’s encounter with Ultima Thule happened so far away that it took six hours for signals travelling at the speed of light to reach Earth.
Scientists didn’t receive confirmation that the spacecraft survived until Tuesday morning, and the first scientific results didn’t start streaming in until that night.
Researchers at the Johns Hopkins University Applied Physics Laboratory in Laurel, Md. — where New Horizons is operated — were up late, working to transform those bits of data into the first high-resolution image of a Kuiper belt object. The black-and-white photo was taken from about 48,280 kilometres away, as New Horizons sped toward its target at 51,499 km/h.
“Spectacular,” principal inves- tigator Alan Stern said at a Wednesday news conference where he displayed the images from the flyby. He described watching his colleagues jump out of their seats and embrace one another upon seeing the crystal-clear image.
“That’s elation,” he said. “And it’s just the tip of the iceberg.”
Scientists had suspected that Ultima Thule would not be perfectly round since the summer of 2017, when a global network of observers found the rock passing in front of a distant star.
But the Kuiper belt object is so distant and so dim that even the most powerful telescopes saw it only as a flicker of light.
Even as New Horizons sped toward its target, in the hours before closest approach, Ultima Thule resembled little more than a blurry bowling pin.
But now “it’s a world,” Stern said — with shape, character and implications for our understanding of planetary science.
Jeff Moore, New Horizons geology team lead, said Ultima Thule likely formed in the first few million years of the solar system from a swirl of smaller objects. Over time, dust and pebbles clumped together to form the object’s two lobes, which eventually combined to form a single body.
This would make Ultima Thule a lot like the worlds — including our own — that ulti- mately formed.
But unlike the planets, which have undergone dramatic geologic change, and comets, which are heated and transformed by the sun, the Kuiper belt object has existed in a “deep freeze” since it first formed, 4.6 billion years ago.
Colour images from New Horizons reveal that, like other Kuiper belt objects, it has a dark reddish hue. This is something of a mystery, because Ultima Thule is thought to be made mostly of ice. But researchers think radiation in this dark and distant part of the solar system could interact with contaminants in the ice, changing their color.