The flyby gave scientists unprecedented insight into Arrokoth’s snowman-like shape, composition and even colour.
Even more incredibly, the mission unfolded some four billion miles away from our planet.
New Horizons Principal Investigator Alan Stern, of the Southwest Research Institute in Boulder, Colorado, shared his excitement about the mission’s results.
He said: “Arrokoth is the most distant, most primitive and most pristine object ever explored by spacecraft, so we knew it would have a unique story to tell.
“It’s teaching us how planetesimals formed, and we believe the result marks a significant advance in understanding overall planetesimal and planet formation.”
The mission’s findings were published across three studies presented at the annual meeting of the American Association for the Advancement of Science on February 13.
The space rocks eventually merged in a “gentle” manner, challenging previously held assumptions planetesimal formation is a violent process.
Lori Glaze, director of NASA’s Planetary Science Division, said: “This is truly an exciting find for what is already a very successful and history-making mission.”
Arrokoth was most likely born during a gravity-driven collapse of a cloud of solid particles in the premolar nebula – a colossal cloud of cosmic material that eventually created the solar system as we know it today.
New Horizons co-investigator William McKinnon said: “Just as fossils tell us how species evolved on Earth, planetesimals tell us how planets formed in space.
“Arrokoth looks the way it does not because it formed through violent collisions, but in more of an intricate dance, in which its component objects slowly orbited each other before coming together.”
Will Grundy from the Lowell Observatory in Flagstaff, Arizona, added: “Arrokoth has the physical features of a body that came together slowly, with ‘local’ materials in the solar nebula.
“An object like Arrokoth wouldn’t have formed, or look the way it does, in a more chaotic accretion environment.”
The New Horizons spacecraft is now approximately 4.4 billion miles (7.1 billion km) from our planet.
The NASA probe is racing deeper into the Kuiper Belt at speeds of about 31,300mph (50,400km/h).