18 Delphini b (abbreviated 18 Del b), formally named Arion /əˈraɪən/,[2] is an extrasolar planet approximately 249 light-years away in the constellation of Delphinus.

A very massive and dense planet with a minimum mass of 10.3 MJ, it was discovered on February 19, 2008, by Bun'ei Sato.

[1] In July 2014, the International Astronomical Union launched NameExoWorlds, a process for giving proper names to certain exoplanets and their host stars.

[5] The winning name was submitted by the Tokushima Prefectural Jonan High School Science Club of Japan.

According to legend, his life was saved at sea by dolphins after attracting their attention by the playing of his kithara[6] ('Delphinus' is Latin for 'dolphin').