The larger lobe, as described by NASA, more closely resembles a giant pancake, while the smaller one is shaped like a dented walnut.
A sequence of images captured as New Horizons moved away from the object in the Kuiper Belt at a velocity of 50,000 km/hour, taken about 10 minutes after closest approach, show a much flatter appearance.
Stringing 14 of the latest images into a short departure movie, New Horizons scientists confirmed that the two sections, or "lobes", of Ultima Thule are not spherical.
Even after New Horizons said goodbye to Ultima Thule, its final glimpse has revealed something completely unexpected.
The bottom view is NASA's current best shape model for Ultima Thule, but still carries some uncertainty as an entire region was essentially hidden from view, and not illuminated by the Sun, during the New Horizons flyby.
They are less certain how the object came to be, which will remain the biggest puzzle they will try to solve in the coming days while waiting for more of New Horizon's last images to arrive. "We've never seen something like this orbiting the Sun", he added.
"The shape model we have derived from all of the existing Ultima Thule imagery is remarkably consistent with what we have learned from the new crescent images", said Simon Porter, a New Horizons co-investigator from the Southwest Research Institute, who leads the shape-modeling effort.
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Ultima Thule - considered a contact binary - is the most distant world ever explored. The images were taken almost 10 minutes after New Horizons crossed its closest approach point.
"This really is an incredible image sequence, taken by a spacecraft exploring a small world 4 billion miles away from Earth, "Stern said".
Though it will take approximately 20 months for New Horizons to get all of its pictures, measurements and other scientific data back home to Earth, the newly released images are sure to "motivate new theories of planetesimal formation in the early solar system", Hal Weaver, New Horizons project scientist from the Johns Hopkins Applied Physics Laboratory, said.
Previously scientists called Ultima Thule "snowman" as the first close-up images revealed its two distinct and spherical segments.
It's hard to see in the video, but scientists have been able to work out more about the object's shape by looking at the way that it blocks out the stars behind it as it passes by. The shape is relatively unprecedented in scientific observations of the solar system. The focal edge of the grouping was gone up against January 1 at 05:42:42 UT (12:42 a.m. EST), when New Horizons was 5,494 miles (8,862 kilometers) past Ultima Thule, and 4.1 billion miles (6.6 billion kilometers) from Earth. By seeing when they blinked out they put together the important new information about the actual shape of Ultima Thule.
A sequence of 14 images taken by New Horizons has been processed and strung together to show the shape and movement of this unusual object.