https://www.scientificamerican.com/article/new-horizons-may-have-solved-planet-formation-cold-case/

Not that long ago, it seemed the glory days of NASA’s New Horizons mission were in the rearview mirror, left behind with its historic Pluto encounter in 2015. Then, early last year, the spacecraft streaked by Arrokoth, a bit of flotsam drifting through the Kuiper Belt—the diffuse ring of primitive icy bodies beyond Neptune, of which Pluto is the largest member. What New Horizons found at Arrokoth—initially reported last year and now reinforced with 10 times more data in three studies published last week in Science—is a critical clue to the greatest cold case in the solar system: the mystery of how planets are born.

“I never expected that our encounter with Arrokoth would be shoulder to shoulder with the Pluto flyby in terms of its importance,” says New Horizons principal investigator and study co-author Alan Stern, a planetary scientist at the Southwest Research Institute. “I didn’t expect to make an earth-shattering discovery about planet formation in the Kuiper Belt, and yet we have. At Arrokoth, we stumbled onto maybe the biggest prize of the entire New Horizons mission.”