This handout image released January 2, 2019 by NASA, the first color image of Ultima Thule, taken at a distance of 85,000 miles (137,000 kilometers) at 4:08 Universal Time on January 1, 2019, highlights its reddish surface. Initially, the New Horizon's team believed that the object was a spherical chunk of ice and rock measuring 18-41 km (10-30 mi) in diameter. By contrast, he suggested, scientists did not know for sure whether other two-lobe bodies - most notably the rubber ducky-like Comet 67P/Churyumov-Gerasimenko - were two objects that came together or one larger body that had eroded into its current shape.
The "snowman", named Ultima Thule, orbits an area known as the Kuiper Belt.
Also of interest is the apparent lack of craters, hinting at a surface built through accretion rather than the violent impacts seen in the inner solar system.
Slowing turning, they eventually touched at each other at what mission geology manager Jeff Moore called an "extremely slow speed" - maybe just one to a few miles per hour.
"If you have a collision with another auto at those speeds, you may not bother to fill out the insurance forms", he joked. "What we're looking at is basically the first planetesimals", Moore said. "These are the only remaining basic building blocks".
Planetary scientists have never before seen a close-up of a body like Ultima Thule. The object may also be a close contact binary asteroid, with a close satellite.
He added that if there was any shock from the Ultima Thule fly-by, it was how fortunate the scientists were for finding it in the Kuiper Belt. The "neck" between the two lobes is particularly bright, perhaps because small, reflective particles tumbled into its crevasse, said Cathy Olkin, a deputy project scientist and planetary scientist at SwRI.
Image caption: This image, taken by the Long-Range Reconnaissance Imager, is the most detailed of Ultima Thule returned so far by the New Horizons spacecraft.
The flow of images and scientific insights is expected to get stronger in the days, weeks and months ahead, as the spacecraft sends back several gigabytes of stored data at a rate of 1,000 bits per second. "It's a snowman if it's anything at all", Stern said amid laughter from the gathered media.
The colour of the object is now confirmed as red.
It dates back to the fourth century, when it was widely used to describe freezing northern lands, both real and fabled. "If that proposal is accepted, we would start a search for [another] object that we could fly by", Stern said. "Just because some bad guys once liked the term, we're not going to let them hijack it". "If there is a connection, it is very tenuous", he said of any Nazi ties to the name, emphasizing the "positive message" of the name. It was chosen from about 34,000 names submitted by an online nomination process.