An Etymological Dictionary of Astronomy and Astrophysics
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A → potentially hazardous asteroid of the → Apollo group. It is approximately 900 m across and displays the characteristics of → C-type asteroids. It was discovered by astronomers with the Lincoln Near-Earth Asteroid Research on May 10, 1999. Ryugu rotates every ~ 7.6 hours and revolves around the Sun in an elongated orbit with an → eccentricity of 0.1902 and a → semi-major axis of 1.1896 → astronomical units (au) in 1.30 years (474 days). Its → aphelion and → perihelion are at 1.4159 au and 0.9633 au, respectively. Ryugu was visited by the Japanese sample-return spacecraft → Hayabusa2 which arrived at the asteroid on June 27, 2018. It studied the asteroid with its several instruments and landers. It is expected to bring surface material to Earth in 2020.

Provisionally named 1999JU₃, Ryugu was officially adopted by the Minor Planet Center on September 28, 2015. The name relates to the Japanese folk tale of the fisherman Urashima Taro. He rescues a turtle from a group of children. The turtle takes him to an underwater palace known as "Ryugu" or "Dragon's Palace." He falls in love with a princess who begs him to stay, but after three days Urashima wishes to return home. As a parting gift, the princess gives the fisherman a box that she tells him never to open. Upon returning home, Urashima is stunned to find that 300 years have passed and everyone he knew has died. In confusion, he opens the box and is encased in a cloud of white fog. When the fog clears, he finds he is an old man, as the box contained his age.