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 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.[2]
| Discovery | |
|---|---|
| Discovered by | Sato et al. |
| Discovery date | 7 February 2007 |
Detection method | Doppler spectroscopy |
| Orbital characteristics | |
Semi-major axis | 1.93 (± 0.03) AU |
| Eccentricity | 0.151 (± 0.023) |
Orbital period (sidereal) | 645.5 (± 5.3) d |
Time of periastron | 2,452,879 ± 12 |
Argument of periastron | 94.4 ± 7.4 |
| Semi-amplitude | 98.5 ± 1.8 |
| Star | Epsilon Tauri |
| Physical characteristics | |
Mean radius | ~1.18 RJ |
| Mass | 7.6 (± 0.2) MJ |
| Temperature | 541 K (268 °C; 514 °F) |
The planet orbits one of the four giant stars in the Hyades cluster that is 2.7 times the mass of the 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 NameExoWorlds, a process for giving proper names to certain exoplanets.[3] The process involved public nomination and voting for the new names.[4] In December 2015, the IAU announced the winning name was Amateru for this planet.[5] 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.[6]
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 REarth) based on its mass, since it is more massive than the jovian planet.
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[7] and has a surface temperature of 5778 K.[8]
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.[2] 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.
The planet Amateru is mentioned by name in the science fiction book Starsong Chronicles: Exodus by American author JJ Clayborn.[9]