Planetary System
On August 17, 2011, European astronomers announced the discovery of three planets orbiting 82 G. Eridani. The mass range of these planets classifies them as super-Earths; objects with only a few times the Earth's mass. These planets were discovered by precise measurements of the radial velocity of the star, with the planets revealing their presence by their gravitational displacement of the star during each orbit. None of the planets display a significant orbital eccentricity. However, their orbital periods are all 90 days or less, indicating that they are orbiting close to the host star. The equilibrium temperature for the most distant planet, based on an assumed Bond albedo of 0.3, would be about 388 K (115 °C); significantly above the boiling point of water.
The number of planets in the system is slightly uncertain. At the time of planet c's detection, it exerted the lowest gravitational perturbation. There was also a similarity noted between its orbital period and the rotational period of the star. For these reasons the discovery team were somewhat more cautious regarding the verity of its candidate planet status than for the other two. Continued observation of the star will be required to determine the exact nature of the planetary system.
An infrared excess was discovered around the star by the Infrared Space Observatory at 60 μm, but was not later confirmed by the Spitzer Space Telescope, in 2006. However, in 2012, a dust disk was found around the star, by the Herschel Space Observatory. While not well-constrained, if assumed to have a similar composition to 61 Virginis' dust disk, it has a semi-major axis of 19 AU.
| Companion |
Mass | Semimajor axis |
Orbital period |
Eccentricity | Radius |
|---|---|---|---|---|---|
| b | ≥2.7 ± 0.3 M⊕ | 0.1207 ± 0.002 | 18.315 ± 0.008 | 0 (fixed) | — |
| c | ≥2.4 ± 0.4 M⊕ | 0.2036 ± 0.0034 | 40.114 ± 0.053 | 0 (fixed) | — |
| d | ≥4.8 ± 0.6 M⊕ | 0.3499 ± 0.0059 | 90.309 | 0 (fixed) | — |
| Dust disk | ~19 AU | ||||
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