Ultima Thule, as the small, icy object has been dubbed, was found to consist of two fused-together spheres, one of them three times bigger than the other, extending about 21 miles (33 kilometers) in length.
After the quick flyby, New Horizons will continue on through the Kuiper Belt with other planned observations of more objects - but the mission scientists said this is the highlight.
Ultima Thule is either one object with two connected lobes, sort of like a spinning bowling pin or peanut still in the shell, or two objects orbiting surprisingly close to one another. Ultima Thule rotates about once every 15 hours, the scientists determined. "What you're seeing is the first contact binary ever explored by a spacecraft", Stern said today at a press conference here at the Johns Hopkins University Applied Physics Laboratory.
"In the coming months, New Horizons will transmit dozens of data sets to Earth, and we'll write new chapters in the story of Ultima Thule - and the solar system", says Helene Winters, New Horizons project manager.
The new images, taken during the New Year's flyby, are the first to confirm that Ultima Thule's teeny waistline is more a juncture than an hourglass.
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NASA said, 'This historic image, the highest resolution image released so far, was made at a range of about 28,000 kilometers only 30 minutes before the New Horizons closest approach. At right, the colour has been overlaid onto the LORRI image to show the colour uniformity of the Ultima and Thule lobes. This is how Ultima Thule is now showing itself to NASA and the rest of the planet from 17,000 miles out: The bowling pin of two days ago has now morphed into a snowman - or BB-8, as the Twitterverse is saying. According to Stern, the team has far less than one percent of all the data now onboard New Horizons in hand.
The New Horizons probe, about the size of a piano, has been flying through space for more than a dozen years and provided the first-ever close-up of Pluto in 2015.
Mark Showalter, a planetary astronomer at the SETI Institute and investigator on the New Horizons mission who led the naming process, told Newsweek that he had never heard of the term before it was picked in a public contest to replace the distant world's technical name, 2014 MU69.
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.
He added: "It is going to revolutionise our knowledge of planetary science". Scientists say no impact craters could be seen in the latest photos.
However, this is just the start, and scientists have promised more details soon. "The data we have look fantastic and we're already learning about Ultima from up close".