The Kuiper Belt object visited by New Horizons in 2019 was Arrokoth, officially designated 486958 Arrokoth.
New Horizons flew past Arrokoth on 1 January 2019, after completing its historic Pluto encounter in 2015. The encounter made Arrokoth the most distant object ever visited by a spacecraft. Because it orbits far beyond Neptune, the flyby gave scientists a rare close look at a primitive body preserved in the cold outer Solar System.
Images revealed that Arrokoth is a contact binary: two lobes joined by a narrow neck. Its distinctive shape was initially compared with a snowman. The two lobes, now formally called Wenu and Weeyo, probably formed separately and merged in an extremely gentle collision. Its reddish, lightly cratered surface may preserve material dating back to the Solar System’s formation about 4.6 billion years ago.
Arrokoth was discovered in 2014 with the Hubble Space Telescope during a search for a reachable New Horizons target. Before receiving its permanent name in 2019, it was widely known by the nickname Ultima Thule. Eris, Haumea and Makemake are also Kuiper Belt or trans-Neptunian objects, but New Horizons did not visit them.