| 18 Delphini b / Arion | |
| Discoverer: | Sato et al. |
| Discovery Site: | Okayama Planet Search Program  Japan |
| Discovered: | 19 February 2008 |
| Discovery Method: | radial velocity |
| Minorplanet: | no |
| Apsis: | astron |
| Semimajor: | 2.6AU |
| Eccentricity: | 0.08 ± 0.01 |
| Period: | 993.3 ± 3.2 d 2.719 y |
| Time Periastron: | 2451672 ± 18 |
| Arg Peri: | 166.1 ± 6.5 |
| Star: | 18 Delphini |
18 Delphini b (abbreviated 18 Del b), formally named Arion, is an extrasolar planet approximately 249 light-years away in the constellation of Delphinus.
The 993-day period planet orbits the yellow giant star 18 Delphini. A very massive and dense planet with a minimum mass of, it was discovered on February 19, 2008, by Bun'ei Sato.
In July 2014, the International Astronomical Union launched NameExoWorlds, a process for giving proper names to certain exoplanets and their host stars.[1] The process involved public nomination and voting for the new names.[2] In December 2015, the IAU announced the name Arion for this planet.[3] The winning name was submitted by the Tokushima Prefectural Jonan High School Science Club of Japan. Arion was a genius of poetry and music in ancient Greece. According to legend, his life was saved at sea by dolphins after attracting their attention by the playing of his kithara[4] ('Delphinus' is Latin for 'dolphin').