18 Delphini b

{{Short description|Extrasolar planet in the constellation Delphinus}}

{{Infobox planet

| name = 18 Delphini b / Arion

| symbol =

| image = Image:18 Del b rv.pdf

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| caption = Radial velocity changes over time of 18 Delphini caused by the orbit of 18 Delphini b.

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| discoverer = Sato et al.

| discovery_site = Okayama Planet
Search Program
{{flag|Japan}}

| discovered = 19 February 2008

| discovery_method = radial velocity

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| minorplanet = no

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| apsis = astron

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| semimajor = {{convert|2.6|AU|km|abbr=on}}

| mean_orbit_radius =

| eccentricity = 0.08 ± 0.01

| period = 993.3 ± 3.2 d
2.719 y

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| long_periastron =

| time_periastron = 2451672 ± 18

| arg_peri = 166.1 ± 6.5

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| star = 18 Delphini

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}}

18 Delphini b (abbreviated 18 Del b), formally named Arion {{IPAc-en|@|'|r|ai|@|n}},{{MW|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 {{Jupiter mass|10.3}}, 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.[http://www.iau.org/news/pressreleases/detail/iau1404/ NameExoWorlds: An IAU Worldwide Contest to Name Exoplanets and their Host Stars]. IAU.org. 9 July 2014 The process involved public nomination and voting for the new names.{{Cite web |url=http://nameexoworlds.iau.org/process |title=NameExoWorlds The Process |access-date=2015-09-05 |archive-date=2015-08-15 |archive-url=https://web.archive.org/web/20150815025117/http://www.nameexoworlds.iau.org/process |url-status=dead }} In December 2015, the IAU announced the name Arion for this planet.[http://www.iau.org/news/pressreleases/detail/iau1514/ Final Results of NameExoWorlds Public Vote Released], International Astronomical Union, 15 December 2015. 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{{Cite web |url=http://nameexoworlds.iau.org/names |title=NameExoWorlds The Approved Names |access-date=2015-12-17 |archive-date=2018-02-01 |archive-url=https://web.archive.org/web/20180201043609/http://nameexoworlds.iau.org/names |url-status=dead }} ('Delphinus' is Latin for 'dolphin').

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