Epsilon Tauri b

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Epsilon Tauri b
Exoplanet List of exoplanets
Epsilon Tauri b.jpg
Artist's impression of Epsilon Tauri b (foreground) orbiting its host star (bottom).
Parent star
Star Epsilon Tauri
Constellation Taurus
Right ascension (α) 04h 28m 37.00s
Declination (δ) +19° 10′ 50″
Apparent magnitude (mV) 3.53
Distance 155 ly
(47.53[1] pc)
Spectral type K0III[2]
Mass (m) 2.7 (± 0.1)[2] M
Radius (r) 12.692 (± 0.545)[3] R
Temperature (T) 4901 (± 20)[2] K
Metallicity [Fe/H] 0.17 (± 0.04)[2]
Age 0.625 (± 0.05)[2] Gyr
Physical characteristics
Mass (m) 7.6 (± 0.2) MJ
Radius (r) ~1.18 RJ
Temperature (T) 541 K (268 °C; 514 °F)
Orbital elements
Semi-major axis (a) 1.93 (± 0.03) AU
Eccentricity (e) 0.151 (± 0.023)
Orbital period (P) 645.5 (± 5.3) d
Argument of
(ω) 94.4 ± 7.4°
Time of periastron (T0) 2,452,879 ± 12 JD
Semi-amplitude (K) 98.5 ± 1.8 m/s
Discovery information
Discovery date 7 February 2007
Discoverer(s) Sato et al.
Discovery method Doppler spectroscopy
Discovery status Confirmed
Database references
Extrasolar Planets
Exoplanet Archive data
Open Exoplanet Catalogue data

Epsilon Tauri b (abbreviated ε Tauri b or ε Tau b), also named Amateru, is a super-Jupiter exoplanet orbiting the K-type giant star Epsilon Tauri approximately 155 light-years (47.53 parsecs, or nearly 1.466×1015 km) away from the Earth in the constellation of Taurus.[1] It orbits the star further out than Earth orbits the Sun. It has moderate eccentricity.[4]

The planet orbits one of the four giant stars in the Hyades cluster that is 2.7 times the mass of our Sun, making it the most massive planet-harboring star. This provides evidence that it was an A-type star when it was on the main-sequence.

In July 2014 the International Astronomical Union (IAU) launched a process for giving proper names to certain exoplanets.[5] The process involved public nomination and voting for the new names.[6] In December 2015, the IAU announced the winning name was Amateru for this planet.[7] The name was based on that submitted by the Kamagari Astronomical Observatory of Kure, Hiroshima Prefecture, Japan: namely 'Amaterasu', the Shinto goddess of the Sun, born from the left eye of the god Izanagi. The IAU substituted 'Amateru' - which is a common Japanese appellation for shrines when they enshrine Amaterasu - because 'Amaterasu' is already used for asteroid 10385 Amaterasu.[8]


Mass, radius and temperature[edit]

Epsilon Tauri b is a "super-Jupiter", an exoplanet that has a radius and mass larger than that of the gas giants Jupiter and Saturn. It has a temperature of 541 K (268 °C; 514 °F). It has an estimated mass of around 7.6 MJ and a potential radius of around 18% larger than Jupiter (1.18 RJ, or 12 R) based on its mass, since it is more massive than the jovian planet.

Host star[edit]

The planet orbits a (K-type) giant star named Epsilon Tauri. It has exhausted the hydrogen supply in its core and is currently fusing helium. The star has a mass of 2.7 M and a radius of around 12.6 R. It has a surface temperature of 4901 K and is 625 million years old. In comparison, the Sun is about 4.6 billion years old[9] and has a surface temperature of 5778 K.[10]

The star's apparent magnitude, or how bright it appears from Earth's perspective, is 3.53. Therefore, Epsilon Tauri can be seen with the naked eye.


Epsilon Tauri b orbits its star with nearly 97 times the Sun's luminosity (97 L) every 645 days at a distance of 1.93 AU (compared to Mars' orbital distance from the Sun, which is 1.52 AU). It has a mildly eccentric orbit, with an eccentricity of 0.15.


Epsilon Tauri b was discovered by using the High Dispersion Echelon Spectrograph at Okayama Astrophysical Observatory (OAO) as part of a process to study G-type and K-type giant stars to search for exoplanets. Measurements of radial velocity from Epsilon Tauri were taken between December 2003 and July 2006.[4] Wobbles in the star were detected, and after analyzing the data, it was eventually concluded that there was a planetary companion with a mass 7 times that of Jupiter orbiting Epsilon Tauri every 645 days, or nearly 2 years with an eccentricity of 0.15.

See also[edit]

In popular culture[edit]

The planet Amateru is mentioned by name in the science fiction book Starsong Chronicles: Exodus by American author JJ Clayborn.[11]


  1. ^ a b "Epsilon Tauri b". NASA Exoplanet Archive. Retrieved 28 July 2016. 
  2. ^ a b c d e "Notes for planet eps Tau b". The Extrasolar Planets Encyclopaedia. Retrieved 2015-09-13. 
  3. ^ Gerard T. van Belle and Kaspar von Braun (2009). "Directly Determined Linear Radii and Effective Temperatures of Exoplanet Host Stars" (abstract). The Astrophysical Journal. 694 (2): 1085–1098. Bibcode:2009ApJ...694.1085V. arXiv:0901.1206Freely accessible. doi:10.1088/0004-637X/694/2/1085. (web Preprint)
  4. ^ a b Sato, Bun'ei; et al. (2007). "A Planetary Companion to the Hyades Giant ε Tauri". The Astrophysical Journal. 661 (1): 527–531. Bibcode:2007ApJ...661..527S. doi:10.1086/513503. 
  5. ^ NameExoWorlds: An IAU Worldwide Contest to Name Exoplanets and their Host Stars. IAU.org. 9 July 2014
  6. ^ NameExoWorlds The Process
  7. ^ Final Results of NameExoWorlds Public Vote Released, International Astronomical Union, 15 December 2015.
  8. ^ NameExoWorlds The Approved Names
  9. ^ Fraser Cain (16 September 2008). "How Old is the Sun?". Universe Today. Retrieved 19 February 2011. 
  10. ^ Fraser Cain (September 15, 2008). "Temperature of the Sun". Universe Today. Retrieved 19 February 2011. 
  11. ^ Clayborn, JJ (March 2017), Starsong Chronicles: Exodus, ISBN 978-1520611747 

External links[edit]

Coordinates: Sky map 04h 28m 37.0s, +19° 10′ 50″