The star
The star
alf Ari
- Type
- K2III
- Surface
- ≈ 4,553 K
- Size
- 13.90 × the Sun
- Mass
- 1.50 × the Sun
- Brightness
- 85.9 × the Sun
- Habitable zone
- 7.4–18.2 AU
The planets
alf Ari
alf Ari b
- Year
- 380.80 days
- Distance from star
- 1.2 AU
- Mass
- at least 1.8 Jupiters
- Size
- 13 × Earth
- Temperature
- ≈ 747 K (+474 °C)
- Found
- 2010, radial velocity (Bohyunsan Optical Astronomical Observatory)
Masses found by the wobble method are minimums, because the orbit's tilt is unknown. Temperatures are equilibrium estimates for a bare planet, before any atmosphere.
How we know
The wobble
The planet tugs its star back and forth. Spectrographs measure the tiny shift in the star's light, which gives the planet's year and a minimum mass.
Sources
- Planet and star parameters: NASA Exoplanet Archive, Planetary Systems Composite Parameters, retrieved 31 Oct 2026. This research has made use of the NASA Exoplanet Archive, which is operated by the California Institute of Technology, under contract with NASA under the Exoplanet Exploration Program.
- Position: HYG Database v4.1 (CC BY-SA 4.0).
- Habitable zone: a simple estimate from the star's brightness (√L × 0.95 to 1.67 AU), shown as a guide.