Scientist Jeff Moore of Nasa's Ames Research Center said the two spheres formed when small, icy pieces coalesced in space billions of years ago.
NASA said it named the larger portion Ultima and the smaller section Thule.
New Horizons rocketed from Cape Canaveral, Florida, in 2006.
Ultima Thule, or more formally 2014 MU69, is a member of the Kuiper Belt, a ring-shaped region of icy objects orbiting the sun. Ultima Thule is about 20 by 10 miles (32 by 16 kilometers) in size, but its composition is still unknown.
"This is what we need to move the models of planetary formation forward", said Alan Stern.
The nature of New Horizons' mission provided NASA with a unique opportunity to explore more of the outer solar system after the 2015 main event.
The New Horizons team has also been able to determine a rough calculation for 2014 MU69's rotation period at 15 hours +/- 1 hour, meaning that more than half of the object was in daylight as New Horizons passed and was therefore observed.
"The data we have look fantastic and we're already learning about Ultima Thule from up close".
According to the BBC, he said: "Everything that we're going to learn about Ultima - from its composition to its geology, to how it was originally assembled, whether it has satellites and an atmosphere, and that kind of thing - is going to teach us about the original formation conditions in the Solar System that all the other objects we've gone out and orbited, flown by and landed on can't tell us because they're either large and evolve, or they are warm". It was the furthest world humankind has ever explored in space.
The colour variation shows just how dark the object is with the brightest areas reflecting just 13 per cent of the light falling on them. The left image is color-enhanced.
While much higher-resolution images will provide a better sense of the topography and geography of 2014 MU69, what is now known is that the bottom, larger lobe ("Ultima") contains changes in elevation greater than one kilometer and that the upper, smaller lobe ("Thule") may contain a plateau feature.
Additional information will be released at 14:00 EST (1900 UTC) Thursday, 3 January 2019 by the New Horizons team.