Epsilon Eridani b

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Epsilon Eridani b / AEgir
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.
Discovery [1]
Discovered by Hatzes et al.
Discovery site United States
Discovery date7 August 2000
Doppler spectroscopy
Orbital characteristics [2]
3.53±0.04  AU
Eccentricity 0.06+0.06
−0.04
7.32±0.07  yr
Inclination 41°+6°
−5°
190°±8°
2458126.5+1657
−502  JD
263°+64°
−184°
Semi-amplitude 10.6  m/s
Star Epsilon Eridani
Physical characteristics
Mass 0.98+0.10
−0.09  MJ [2]

    Epsilon Eridani b, formally named AEgir[ sic ], [3] 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 2024 remains the only confirmed planet in its planetary system. It is a remarkably close analog to Jupiter, with similar mass and orbit. [2]

    Contents

    Name

    The planet and its host star are one of the planetary systems selected by the International Astronomical Union as part of NameExoWorlds, their public process for giving proper names to exoplanets and their host star (where no proper name already exists). [4] [5] The process involved public nomination and voting for the new names. [6] In December 2015, the IAU announced the winning names were AEgir [ sic ] for the planet (pronounced /ˈiːdʒər/ [Anglicized] or /ˈeɪjɪər/ , an approximation of the old Norse Ægir) and Ran for the star. [7] James Ott, age 14, submitted the names for the IAU contest and won. [8]

    The moon Aegir of Saturn is also named after the mythological Ægir, and differs in spelling only by capitalization. [9]

    Characteristics

    Orbit

    Orbit of Epsilon Eridani b as seen from the Solar System Orbit of Epsilon Eridani b at 2025-03-03.png
    Orbit of Epsilon Eridani b as seen from the Solar System

    The semi-major axis of Epsilon Eridani b's orbit is 3.53 AU, and the planet completes an orbit around its star every 7.32 years. The orbit is nearly circular, having a low eccentricity of 0.06+0.06
    −0.04    , comparable to Jupiter's eccentricity of approximately 0.05. [2]

    Viewed from the Solar System, Epsilon Eridani b's orbit is inclined from face-on orientation by 41° . The planet's orbital plane is found to be close to coplanar with the main belt, with mutual inclination of 4–16°. [2]

    Mass

    Epsilon Eridani b's true mass is 0.98 Jupiter masses, although the inclination of its orbit caused the minimum mass measured by the radial velocity method to be 0.63 Jupiter masses. [2]

    History of observations

    Discovery

    The existence of a planet around Epsilon Eridani was suspected by a Canadian team led by Bruce Campbell and Gordon Walker since 1988, but their observations were not definitive enough to make a solid discovery. [10] [11]

    Its formal discovery was announced on 7 August, 2000, by a team led by Artie Hatzes. The discoverers gave its minimum mass as 0.86 Jupiter masses, with a semi-major axis of 3.3 AU and eccentricity of 0.6. [1] 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. [12]

    The planet continued to be detected in subsequent observations over the following years. In 2006, utilizing new radial velocity data, a team of researchers found the planet to reside in a more circular orbit, with an eccentricity of 0.25, as well as finding a minimum mass of 1.06 Jupiter masses and a semi-major axis of 3.38 AU. [13] Later that year, astrometric measurements made by the Hubble Space Telescope showed that the planet's orbit shares the same plane as the outer dust disk observed around the star, and is highly eccentric, at an eccentricity of 0.702, while its mass was found to be 1.55 Jupiter masses. [14]

    Planet challenged

    In 2009, the Spitzer Space Telescope detected an inner warm belt located at roughly 3 AU from the star. [15] A team of astronomers found that the high eccentricity of the planet and this belt were inconsistent, as the planet would pass through the belt and rapidly clear it of material, although they may be reconciled if the true eccentricity of the planet was lower, [16] or if the belt's material had migrated in from the outer comet belt (also known to exist). [17]

    The existence of the planet itself came into doubt when two papers published in 2012 and 2013 failed to recover the planet previously found in the radial velocity data, suggesting that the signal may, in fact, be stellar activity of the parent star instead, or at least the planet has very different properties from what previous papers reported. [18] [19] The nondetection of Epsilon Eridani b was not unanimous, however, as a paper from 2016 found the stellar activity to be uncorrelated to the planetary signal previously claimed, strengthening the case for a planet. [20]

    A paper published in January 2019 successfully detected Epsilon Eridani b, and found an orbital eccentricity of around 0.07, much smaller than previous estimate and consistent with a nearly circular orbit. [21] This resolved the stability issue with the inner asteroid belt. The updated measurements also included new estimate for the mass of the planet, at 0.78 Jupiter masses, but the poorly constrained inclination of 89°±42° meant this was only a rough estimate of the absolute mass. [21] If the planet instead orbited at the same inclination as the debris disc (34°), as supported by Benedict et al. 2006, [14] then its mass would have been greater, at approximately 1.19 Jupiter masses. [21]

    The existence of the planet was further corroborated by astrometric observations. [22]

    Inconsistent orbital solutions

    Since 2019, several papers have characterized the planet's orbit and mass using radial velocity data, often in conjunction with astrometric data, and upper limits from non-detection via direct imaging. These papers found different and inconsistent orbital solutions, owing to different datasets and methodologies, [2] with the planet's true mass values ranging from 0.6 to 0.8 Jupiter masses, eccentricities ranging from nearly circular orbit [23] [24] to significantly eccentric, [25] and inclinations between 45° [26] and 78°. [27]

    Direct imaging

    The James Webb Space Telescope observed Epsilon Eridani between December 2024 and February 2025, when the angular separation between the star and the planet was expected to be at its maximum, in order to acquire direct image of the planet, as well as its spectrum. [28] Multiple direct imaging efforts of this planet has been unsuccessfully conducted in the past, serving to place upper limits on its brightness. [2]

    See also

    References

    1. 1 2 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. S2CID   117865372.
    2. 1 2 3 4 5 6 7 8 Thompson, William; Nielsen, Eric; Ruffio, Jean-Baptiste; Blunt, Sarah; Marois, Christian (2025-02-27). "Revised Mass and Orbit of $\varepsilon$ Eridani b: A 1 Jupiter-Mass Planet on a Near-Circular Orbit". arXiv.org. Retrieved 2025-03-03.
    3. ↑ 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
    4. ↑ "NameExoWorlds: An IAU Worldwide Contest to Name Exoplanets and their Host Stars". IAU.org. 9 July 2014. Retrieved 2017-09-25.
    5. ↑ "The ExoWorlds". nameexoworlds.iau.org: IAU. Archived from the original on 2016-12-31. Retrieved 2017-09-25.
    6. ↑ "NameExoWorlds". nameexoworlds.iau.org: IAU. Retrieved 2017-09-25.
    7. ↑ "Final Results of NameExoWorlds Public Vote Released". International Astronomical Union. 15 December 2015. Retrieved 2017-09-25.
    8. ↑ "Mountainside wins competition to name planet, star". Spokesman.com. Retrieved 2016-05-12.
    9. ↑ "Planetary Names". planetarynames.wr.usgs.gov. Retrieved 6 January 2023.
    10. ↑ Campbell, Bruce; Walker, G. A. H.; Yang, S. (1988). "A search for substellar companions to solar-type stars". The Astrophysical Journal. 331. American Astronomical Society: 902. Bibcode:1988ApJ...331..902C. doi: 10.1086/166608 . ISSN   0004-637X.
    11. ↑ Walker, Gordon A.H.; Walker, Andrew R.; Irwin, Alan W.; Larson, Ana M.; Yang, Stephenson L.S.; Richardson, Derek C. (1995). "A Search for Jupiter-Mass Companions to Nearby Stars". Icarus. 116 (2). Elsevier BV: 359–375. Bibcode:1995Icar..116..359W. doi:10.1006/icar.1995.1130. ISSN   0019-1035.
    12. ↑ 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.
    13. ↑ 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. S2CID   119067572.
    14. 1 2 Benedict, G. Fritz; 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. S2CID   18603036 . Retrieved 2008-11-16.
    15. ↑ 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. S2CID   18183427.
    16. ↑ 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 .
    17. ↑ Reidemeister, Martin; et al. (2011). "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. S2CID   56019152.
    18. ↑ Anglada-Escudé, Guillem; Butler, R. Paul (2012-06-01). "The HARPS-TERRA Project. I. Description of the Algorithms, Performance, and New Measurements on a Few Remarkable Stars Observed by HARPS". The Astrophysical Journal Supplement Series. 200 (2): 15. arXiv: 1202.2570 . Bibcode:2012ApJS..200...15A. doi: 10.1088/0067-0049/200/2/15 . ISSN   0067-0049.
    19. ↑ Zechmeister, M.; Kürster, M.; Endl, M.; Curto, G. Lo; Hartman, H.; Nilsson, H.; Henning, T.; Hatzes, A. P.; Cochran, W. D. (2013-04-01). "IV. The search for Jupiter analogues around solar-like stars" (PDF). Astronomy & Astrophysics. 552. EDP Sciences. arXiv: 1211.7263 . Bibcode:2013A&A...552A..78Z. doi: 10.1051/0004-6361/201116551 . ISSN   0004-6361.
    20. ↑ Howard, Andrew W.; Fulton, Benjamin J. (2016-11-01). "Limits on Planetary Companions from Doppler Surveys of Nearby Stars". Publications of the Astronomical Society of the Pacific. 128 (969): 114401. arXiv: 1606.03134 . Bibcode:2016PASP..128k4401H. doi: 10.1088/1538-3873/128/969/114401 . ISSN   0004-6280.
    21. 1 2 3 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. S2CID   119350738.
    22. ↑ Makarov, Valeri V.; Zacharias, Norbert; Finch, Charles T. (2021). "Looking for Astrometric Signals below 20 m s−1: A Jupiter-mass Planet Signature in ε Eri". Research Notes of the AAS. 5 (6): 155. arXiv: 2107.01090 . Bibcode:2021RNAAS...5..155M. doi: 10.3847/2515-5172/ac0f59 . We conclude that the newest astrometric results confirm the existence of a long-period exoplanet orbiting ε Eri....The results are consistent with the previously reported planet epsEri-b of approximately Jupiter mass and a period of several years.
    23. ↑ Rosenthal, Lee J.; Fulton, Benjamin J.; et al. (2021-07-01). "The California Legacy Survey. I. A Catalog of 178 Planets from Precision Radial Velocity Monitoring of 719 Nearby Stars over Three Decades". The Astrophysical Journal Supplement Series. 255 (1). American Astronomical Society: 8. arXiv: 2105.11583 . Bibcode:2021ApJS..255....8R. doi: 10.3847/1538-4365/abe23c . ISSN   0067-0049. S2CID   235186973.
    24. ↑ Roettenbacher, Rachael M.; Cabot, Samuel H. C.; Fischer, Debra A.; Monnier, John D.; Henry, Gregory W.; Harmon, Robert O.; Korhonen, Heidi; Brewer, John M.; Llama, Joe; Petersburg, Ryan R.; Zhao, Lily L.; Kraus, Stefan; Le Bouquin, Jean-Baptiste; Anugu, Narsireddy; Davies, Claire L.; Gardner, Tyler; Lanthermann, Cyprien; Schaefer, Gail; Setterholm, Benjamin; Clark, Catherine A.; Jorstad, Svetlana G.; Kuehn, Kyler; Levine, Stephen (2022-01-01). "EXPRES. III. Revealing the Stellar Activity Radial Velocity Signature of ϵ Eridani with Photometry and Interferometry". The Astronomical Journal. 163 (1): 19. arXiv: 2110.10643 . Bibcode:2022AJ....163...19R. doi: 10.3847/1538-3881/ac3235 . ISSN   0004-6256.
    25. ↑ Feng, Fabo; Butler, R. Paul; et al. (July 2023). "Revised orbits of the two nearest Jupiters". Monthly Notices of the Royal Astronomical Society . 525 (1): 607–619. arXiv: 2307.13622 . Bibcode:2023MNRAS.525..607F. doi: 10.1093/mnras/stad2297 .
    26. ↑ Benedict, G. Fritz (March 2022). "Revisiting HST/FGS Astrometry of epsilon Eridani". Research Notes of the AAS . 6 (3): 45. Bibcode:2022RNAAS...6...45B. doi: 10.3847/2515-5172/ac5b6b .
    27. ↑ Llop-Sayson, Jorge; Wang, Jason J.; Ruffio, Jean-Baptiste; Mawet, Dimitri; et al. (6 October 2021). "Constraining the Orbit and Mass of epsilon Eridani b with Radial Velocities, Hipparcos IAD-Gaia DR2 Astrometry, and Multiepoch Vortex Coronagraphy Upper Limits". The Astronomical Journal. 162 (5): 181. arXiv: 2108.02305 . Bibcode:2021AJ....162..181L. doi: 10.3847/1538-3881/ac134a . eISSN   1538-3881. ISSN   0004-6256. S2CID   236924533.
    28. ↑ "First image and spectrum of a true Jupiter-Saturn Analog". STScI . Retrieved 29 February 2024. We propose to take the first image and spectrum of a true Solar System gas giant analog, the emblematic eps Eridani b, with the NIRSpec integral field unit (IFU).
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