However, the new images - taken from as close as 27,000 kilometres on approach - revealed Ultima Thule as a "contact binary", consisting of two connected spheres, resembling a snowman. Together they form Ultima Thule, a frozen world that is almost 4.5 billion miles from Earth, more distant than Pluto.
In a lengthy update by the New Horizons team, the group boasts that New Horizons sent back a signal to its handlers letting them know that it had filled its on-board recorders with a wealth of science data that it collected as it zoomed past Ultima Thule.
The same kind of accretion process produced the other moons and planets of the solar system around 4.5 billion years ago, says Jeff Moore, a co-investigator on NASA's New Horizons mission. That means it is a single object, with two lobes, but the lobes are gently in contact. Ultima Thule rotates about once every 15 hours, the scientists determined.More news: Pelosi says Democrats will give "nothing for the wall"
All of this information came from "far less than 1% of the data on New Horizons that has reached the ground", said Alan Stern, mission principal investigator at the Southwest Research Institute. End to end, the object measures 19 miles in length.
The selection of Ultima Thule as a next target after New Horizons' July 14, 2015 flyby of Pluto was largely determined by its being one of the more promising candidates that could be reached on its trajectory without a significant - and fuel-consuming - change of course.
Shortly after the encounter, New Horizons beamed back a handful of initial images showing a bowling pin-shaped object.
Planetary scientists have never before seen a close-up of a body like Ultima Thule.More news: Tops on House Dems to-do list: Try to end shutdown
"New Horizons holds a dear place in our hearts as an intrepid and persistent little explorer, as well as a great photographer", said Dr. Ralph Semmel, Director of Johns Hopkins Applied Physics Laboratory.
"They're clearly two objects that have come together", says New Horizons' Deputy Project Scientist Cathy Olkin.
"Just because some bad guys once liked that term", he said, "we're not going to let them hijack it". "We are seeing a physical representation of the beginning of planetary formation, frozen in time", he said.
The shape of Ultima Thule had been the subject of speculation for years leading up to the flyby. Now, May has combined both of his loves on "New Horizons", his first solo song in more than two decades. The pea shape is now no more relevant, and ultimately the scientists have been to the conclusion that the shape of the Ultima Thule is like that of a snowman.More news: Have you seen 'Bird Box'? Netflix says basically everyone else has
As a preserved relic from that original time, Ultima Thule also promises to shed light on the so-called Kuiper Belt, or Twilight Zone, in which hundreds of thousands of objects reside well beyond Neptune.