But, it spins end-over-end like a propeller.
The latest images upended the initial assumptions, showing it isn't actually made up of spheroidal segments, as first thought - instead, its two lobes are flat like pancakes.
"While the very nature of a fast flyby in some ways limits how well we can determine the true shape of Ultima Thule, the new results clearly show that Ultima and Thule are much flatter than originally believed, and much flatter than expected", said Hal Weaver, New Horizons project scientist from the Johns Hopkins Applied Physics Laboratory.
The images of the KBO - officially named 2014 MU69 - were captured by the New Horizons as it raced away at over 50,000 kilometers per hour on January 1.
NASA scientists shared the 3D animation of the space rock's shape below, which was created using images that New Horizons captured as it left MU69 behind.
'It would be closer to reality to say Ultimate Thule's shape is flatter, like a pancake.
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", Alan Stern, principal investigator on the New Horizons mission, said in a press release.
However, more analysis of approach images and these new departure images have changed that view, in part by revealing an outline of the portion of the KBO that was not illuminated by the Sun, but could be "traced out" as it blocked the view to background stars.
MU69 exists in an arrangement known as a contact binary - and, it's now the first a spacecraft has ever explored.
The primitive world was "born" this way, and did not evolve or deform through external processes to take on the unusual shape, the team explains.
New Horizons may have moved on from Ultima Thule, but it still has plenty of images stored in its robotic brain. The shape is relatively unprecedented in scientific observations of the solar system.
The images that shocked New Horizons' scientists will be available on the New Horizons LORRI website this week. 'It's a snowman, if anything at all'.
It is safe to say the new apparent shape of Ultima Thule will only increase the interest of scientists studying this object-humans have never observed an object like this in the distant Kuiper Belt so closely before. The small, icy object is shown spinning end-over-end like a propeller.