486958 Arrokoth

486958 Arrokoth (provisional designation ; formerly nicknamed Ultima Thule) is a trans-Neptunian object located in the Kuiper belt. Arrokoth became the farthest and most primitive object in the Solar System visited by a spacecraft when the NASA space probe New Horizons conducted a flyby on 1 January 2019. Arrokoth is a contact binary long, composed of two planetesimals across, that are joined along their major axes. With an orbital period of about 298 years and a low orbital inclination and eccentricity, Arrokoth is classified as a cold classical Kuiper belt object. Arrokoth was discovered on 26 June 2014 by astronomer Marc Buie and the New Horizons Search Team using the Hubble Space Telescope as part of a search for a Kuiper-belt object for New Horizons to target in its first extended mission; it was chosen over two other candidates, and , to become the primary target of the mission. When Arrokoth was first observed by the Hubble Space Telescope in 2014, it was designated in the context of the telescope's search for Kuiper belt objects, and was nicknamed "11" for short. Its existence as a potential target of the New Horizons probe was announced by NASA in October 2014 and it was unofficially designated as "Potential Target 1", or . Its official provisional designation, , was assigned by the Minor Planet Center in March 2015, after sufficient orbital information had been gathered. The provisional designation indicates that Arrokoth was the 1745th minor planet to be assigned a provisional designation during the second half of June 2014. After further observations refining its orbit, it was given the permanent minor planet number 486958 on 12 March 2017. Before the flyby on 1 January 2019, NASA invited suggestions from the public on a nickname to be used for the object. One of the choices, Ultima Thule, was selected on 13 March 2018. Thule (Θούλη, ) is the northernmost location mentioned in ancient Greek and Roman literature and cartography, while in classical and medieval literature ultima Thule (Latin for 'farthermost Thule') acquired a metaphorical meaning of any distant place located beyond the "borders of the known world".