"Last night, the United States spacecraft New Horizons conducted the farthest exploration in the history of humankind, and did so spectacularly", said Alan Stern, principal investigator.
Scientists chose to study Ultima Thule with New Horizons after the spaceship, which launched in 2006, completed its main mission of flying by Pluto in 2015, returning the most detailed images ever taken of the dwarf planet. Scientists say it will take almost two years for New Horizons to beam back all its observations of Ultima Thule, a full billion miles (1.6 billion kilometers) beyond Pluto. It's small, about 20 miles across, and, as seen in the first rudimentary images, seems to be shaped like a bowling pin.
But despite the festive atmosphere - which included the release of a New Horizons song recorded by contributing scientist and rock guitarist Brian May of Queen, who was on hand for the event - the mission team had no way of knowing if their spacecraft was still in one piece and executing its reconnaissance of Ultima Thule.
For Ultima Thule - which wasn't even known when New Horizons departed Earth in 2006 - the endeavour was more hard.
The flyby comes 3½ years after New Horizons swung past Pluto and yielded the first close-ups of the dwarf planet.
NASA's New Horizons probe has flown past Ultima Thule - a ball of dust and ice that's 6.5 billion kilometres from Earth.
Ultima Thule is a Kuiper Belt object that sits one billion miles past Pluto.
Scientists rejoiced at the Johns Hopkins Applied Physics Laboratory (APL) today at 10:29 a.m. EST, saying the moment ushered in the new era of "exploration from the enigmatic Kuiper Belt, a region of primordial objects that holds keys to understanding the origins of the solar system".
The New Horizons spacecraft flew by Ultima Thule at a distance of 3,500 km.
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An image of Thule, sent overnight and barely more detailed than previous images, deepens the mystery of whether Thule is a single rock shaped like an asymmetrical peanut or actually two rocks orbiting each other, "blurred together due to their proximity", Stern said.
The New Horizons probe was slated to reach the "third zone" in the uncharted heart of the Kuiper Belt at 12.33am Eastern (1.33pm Malaysian time).
Scientists are not sure exactly what Ultima Thule (pronounced TOO-lee) looks like - whether it is cratered or smooth, or even if it is a single object or a cluster.
Engineers at Johns Hopkins Applied Physics Laboratory in Maryland cheered when the spacecraft's first signals came through the National Aeronautic and Space Agency's Deep Space Network at 10.28am on Tuesday (local time).
Just hours into 2019, the New Horizons spacecraft was confirmed to have made its flyby of the mysterious Kuiper Belt object Ultima Thule without issue.
"Its geology and composition should teach us a lot about how these building blocks of small planets like Pluto were formed".
"Ultima Thule is 17,000 times as far away as the "giant leap" of Apollo's lunar missions".
Ultima Thule is named for a mythical, far-northern island in medieval literature and cartography, according to NASA.
Stern said the science team expects to use the data to map the surface and look for satellites and rings around Ultima Thule, Stern said. "So stay tuned. There are no second chances for New Horizons". He noted it took 12 years to sell the project, five years to build it and nine years to reach the first target, Pluto.