Epsilon Tauri b

Epsilon Tauri b (abbreviated ε Tauri b or ε Tau b), formally named Amateru /æməˈtɛruː/, is a super-Jupiter exoplanet orbiting the K-type giant star Epsilon Tauri approximately 146 light-years (45 parsecs) away from the Earth in the constellation of Taurus.^[3] It orbits the star further out than Earth orbits the Sun. It has moderate eccentricity.^[1]

Epsilon Tauri b / Amateru

Artistic simulation of Epsilon Tauri b orbiting its host star.
Discovery[1]
Discovered by	Sato et al.
Discovery date	7 February 2007
Detection method	Doppler spectroscopy
Orbital characteristics[2]
Semi-major axis	1.878±0.001 AU
Eccentricity	0.076+0.009 −0.008
Orbital period (sidereal)	585.82+0.26 −0.33 d
Time of periastron	2453492.3+11.3 −10.0 JD
Argument of periastron	107.90°+6.82° −6.07°
Semi-amplitude	93.24+0.74 −0.73 m/s
Star	Epsilon Tauri
Physical characteristics[2]
Mass	≥7.190±0.056 MJ

The planet orbits one of the four giant stars in the Hyades star cluster, and was the first planet ever discovered in an open cluster.^[1]

Name

In July 2014, the International Astronomical Union (IAU) launched NameExoWorlds, a process for giving proper names to certain exoplanets.^[4] The process involved public nomination and voting for the new names.^[5] In December 2015, the IAU announced the winning name was Amateru for this planet.^[6] 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.^[7]

Characteristics

Mass, radius and temperature

Epsilon Tauri b is a "super-Jupiter", an exoplanet that has a mass larger than that of the gas giants Jupiter and Saturn. It has a temperature of 541 K (268 °C; 514 °F).^{[citation needed]} It has a minimum mass of around 7.2 M_J^[2] and a potential radius of around 18% larger than Jupiter (1.18 R_J, or 12 R_🜨) based on its mass, since it is more massive than the jovian planet.^{[citation needed]}

Host star

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^[8] and has a surface temperature of 5778 K.^[9]

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.

Orbit

Epsilon Tauri b orbits its star with about 78 times the Sun's luminosity (78 L_☉) every 586 days at a distance of 1.88 AU (compared to Mars' orbital distance from the Sun, which is 1.52 AU). It has a mildly eccentric orbit, with an eccentricity of 0.08.^[2]

Discovery

Epsilon Tauri b was discovered by using the High Dispersion Echelle 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.^[1] 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 595 days, or nearly 2 years with an eccentricity of 0.15.^[1] These values were later refined to a period of 586 days and an eccentricity of 0.08.^[2]

In popular culture

The planet Amateru is mentioned by name in the science fiction book Starsong Chronicles: Exodus by American author JJ Clayborn.^[10]

See also

• 4 Ursae Majoris b
• Epsilon Eridani b
• Epsilon Reticuli Ab