Epsilon Eridani b

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Epsilon Eridani b
Epsilon Eridani b.jpg
An artist's impression of Epsilon Eridani b, depicting it as a gas giant with rings. The object near the bottom is a hypothetical moon.
Discovered byHatzes et al.
Discovery siteUnited States
Discovery date7 August 2000
Doppler spectroscopy
Orbital characteristics[1]
3.48±0.02 AU
7.37±0.07 y
Semi-amplitude11.48±0.66 m/s
StarEpsilon Eridani
Physical characteristics[1]
Mass1.19±0.12 MJ
Temperature~150 K (−123 °C; −190 °F)

Epsilon Eridani b, also known as AEgir,[2] is an exoplanet approximately 10.5 light-years away orbiting the star Epsilon Eridani, in the constellation of Eridanus (the River). The planet was discovered in 2000, and as of 2019 remains the only confirmed planet in its planetary system. It orbits at around 3.5 AU with a period of around 7.4 years, and has a mass around 1.2 times that of Jupiter.


The planet and its host star are one of the planetary systems selected by the International Astronomical Union as part of their public process for giving proper names to exoplanets and their host star (where no proper name already exists).[3][4] The process involved public nomination and voting for the new names.[5] In December 2015, the IAU announced the winning names were AEgir for the planet (pronounced /ˈər/ [Latinized] or /ˈjɪər/, an approximation of the old Norse Ægir) and Ran for the star.[6] James Ott, age 14, submitted the names for the IAU contest and won.[7]


The planet's existence was suspected by a Canadian team led by Bruce Campbell and Gordon Walker in the early 1990s, but their observations were not definitive enough to make a solid discovery. Its formal discovery was announced on August 7, 2000 by a team led by Artie Hatzes. The discoverers gave its mass as 1.2 ± 0.33 times that of Jupiter, with a mean distance of 3.4 AU from the star.[8] Observers, including Geoffrey Marcy, suggested that more information on the star's Doppler noise behaviour created by its large and varying magnetic field was needed before the planet could be confirmed.[9]

In 2006, the Hubble Space Telescope made astrometric measurements and confirmed the existence of the planet.[10] These observations indicated that the planet has a mass 1.5 times that of Jupiter and shares the same plane as the outer dust disk observed around the star.[11] The derived orbit from these measurements is eccentric: either 0.25[11] or 0.7.[12]

Meanwhile, the Spitzer Space Telescope detected an asteroid belt at roughly 3 AU from the star.[13] In 2009 Brogi's team claimed that the proposed planet's eccentricity and this belt were inconsistent: the planet would pass through the asteroid belt and rapidly clear it of material.[14] The planet and the inner belt may be reconciled if that belt's material had migrated in from the outer comet belt (also known to exist).[15]

Astronomers are still collecting and analysing radial velocity data, while also trying to refine existing upper limits from direct imaging, on Epsilon Eridani b. A paper published in January 2019 finds an orbital eccentricity an order of magnitude smaller than earlier estimates, at around 0.07 and consistent with a circular orbit, very similar to Jupiter's orbital eccentricity of 0.05.[1] This resolves the stability issues with the inner asteroid belt. The updated measurements, amongst other things, also include new estimates for the mass and inclination of the planet, at 0.78 times the mass of Jupiter given a poorly constrained inclination of around 89 degrees.[1] If the planet instead orbits at the same inclination as the debris disc (34 degrees), as supported by Benedict et al. 2006,[11] then its mass would be greater, at 1.19 times that of Jupiter.[1]

As of 2021, both the Extrasolar Planets Encyclopaedia and the NASA Exoplanet Archive list the planet as 'confirmed'.[16][17]

See also[edit]



  1. ^ a b c d e Mawet, Dimitri; Hirsch, Lea; et al. (2019). "Deep Exploration of ϵ Eridani with Keck Ms-band Vortex Coronagraphy and Radial Velocities: Mass and Orbital Parameters of the Giant Exoplanet" (PDF). The Astronomical Journal. 157 (1): 33. arXiv:1810.03794. Bibcode:2019AJ....157...33M. doi:10.3847/1538-3881/aaef8a. ISSN 1538-3881. OCLC 7964711337.
  2. ^ Carroll, Michael (2017), "Zeroing in on Earth 2.0", Earths of Distant Suns, Springer, p. 79, doi:10.1007/978-3-319-43964-8_5, ISBN 978-3-319-43963-1, Planet name: AEgir | Original designation: Epsilon Eridani b
  3. ^ "NameExoWorlds: An IAU Worldwide Contest to Name Exoplanets and their Host Stars". IAU.org. 9 July 2014. Retrieved 2017-09-25.
  4. ^ "The ExoWorlds". nameexoworlds.iau.org: IAU. Archived from the original on 2016-12-31. Retrieved 2017-09-25.
  5. ^ "NameExoWorlds". nameexoworlds.iau.org: IAU. Retrieved 2017-09-25.
  6. ^ "Final Results of NameExoWorlds Public Vote Released". International Astronomical Union. 15 December 2015. Retrieved 2017-09-25.
  7. ^ "Mountainside wins competition to name planet, star". Spokesman.com. Retrieved 2016-05-12.
  8. ^ Hatzes, Artie P.; et al. (2000). "Evidence for a Long-Period Planet Orbiting ε Eridani". The Astrophysical Journal. 544 (2): L145–L148. arXiv:astro-ph/0009423. Bibcode:2000ApJ...544L.145H. doi:10.1086/317319.
  9. ^ Marcy, Geoffrey W.; et al. (August 7–11, 2000). "Planetary Messages in the Doppler Residuals (Invited Review)". In A. Penny (ed.). Planetary Systems in the Universe, Proceedings of IAU Symposium #202. Manchester, United Kingdom. p. 20–28. Bibcode:2004IAUS..202...20M.
  10. ^ "Hubble Zeroes in on Nearest Known Exoplanet". Hubble News Desk. 2006-10-09. Retrieved 2006-10-10.
  11. ^ a b c Benedict; et al. (2006). "The Extrasolar Planet ε Eridani b: Orbit and Mass". The Astronomical Journal. 132 (5): 2206–2218. arXiv:astro-ph/0610247. Bibcode:2006AJ....132.2206B. doi:10.1086/508323. Retrieved 2008-11-16.
  12. ^ Butler; et al. (2006). "Catalog of Nearby Exoplanets". The Astrophysical Journal. 646 (1): 505–522. arXiv:astro-ph/0607493. Bibcode:2006ApJ...646..505B. doi:10.1086/504701.
  13. ^ Backman, D.; et al. (2009). "Epsilon Eridani's Planetary Debris Disk: Structure and Dynamics Based on Spitzer and Caltech Submillimeter Observatory Observations". The Astrophysical Journal. 690 (2): 1522–1538. arXiv:0810.4564. Bibcode:2009ApJ...690.1522B. doi:10.1088/0004-637X/690/2/1522.
  14. ^ Brogi, M.; et al. (2009). "Dynamical stability of the inner belt around Epsilon Eridani". Astronomy and Astrophysics. 499 (2): L13–L16. Bibcode:2009A&A...499L..13B. doi:10.1051/0004-6361/200811609.
  15. ^ Martin Reidemeister; et al. (2010). "The cold origin of the warm dust around epsilon Eridani". Astronomy & Astrophysics. 527: A57. arXiv:1011.4882. Bibcode:2011A&A...527A..57R. doi:10.1051/0004-6361/201015328.
  16. ^ "Planet eps Eridani b". exoplanet.eu. Extrasolar Planets Encyclopaedia. Retrieved 30 March 2021. Planet Status: Confirmed
  17. ^ "eps Eri Overview". NASA Exoplanet Archive. NASA Exoplanet Science Institute. Retrieved 30 March 2021. Status: Confirmed Planet

External links[edit]

Coordinates: Sky map 03h 32m 55.8442s, −09° 27′ 29.744″