alf Ari b
Astrophysical Synthesis & Habitability Characterization
alf Ari b is a confirmed gas giant exoplanet orbiting the star alf Ari, located approximately 65.9 light-years (20.21 parsecs) from the Solar System. First announced in 2010 by Bohyunsan Optical Astronomical Observatory using the Radial Velocity detection technique (measuring periodic Doppler reflex motion in the host star's spectrum), this world measures 13.4 Earth radii (1.2 Jupiter radii) and has a measured mass of 572.07 Earth masses (1.8 Jupiter masses). Combining its mass and radius yields a mean bulk density of 1.31 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 3.19 g⊕ (31.28 m/s²), and an escape velocity of 73.1 km/s.
In its orbital architecture around alf Ari, alf Ari b completes one full revolution every 380.8 Earth days (1.04Julian years) at a semi-major axis of 1.2 AU (comparable to the inner terrestrial zone between Venus, Earth at 1.00 AU, and Mars at 1.52 AU). Its mean orbital velocity is approximately 34.3 km/s (compared to Earth's 29.8 km/s). The planet follows a highly eccentric trajectory (e = 0.25, swinging from 0.9 AU at periapsis out to 1.5 AU at apoapsis), pointing to past dynamical scattering or secular gravitational perturbations.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 747 K (+474°C / +885°F) and receiving 59.65 S⊕ (~81,189 W/m²), alf Ari b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star alf Ari is classified as an orange K-type star of spectral type K2III with an effective photospheric temperature of 4,553 K, a radius of 13.9 R☉, a mass of 1.5 M☉, an estimated bolometric luminosity of 74.492 L☉. Stellar evolution modeling indicates a metallicity of [Fe/H] = -0.09 dex (near-solar heavy-element abundance). From Earth, alf Ari shines at apparent V-band magnitude 2.005 (visible to the unaided human eye under dark skies) in the Northern celestial hemisphere.
Methodology: Computed using the Schulze-Makuch et al. (2011) weighted metric comparing physical interior (radius, estimated density) and surface thermal regime (escape velocity, equilibrium temperature).
Discovery Facility: Bohyunsan Optical Astronomical Observatory · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | alf Ari |
| Spectral Type | K2III |
| Effective Temp (Teff) | 4,553 K |
| Stellar Radius | 13.9000 R☉ |
| Stellar Mass | 1.5000 M☉ |
| Bolometric Luminosity | 74.492 L☉ |
| Metallicity [Fe/H] | -0.090 dex |
| Stellar Age | — |
| Apparent Magnitude | V: 2.005 |
| System Architecture | 1 Star, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 1.200000 AU |
| Orbital Period | 380.8 days |
| Mean Orbital Velocity | 34.3 km/s |
| Orbital Eccentricity (e) | 0.25000 |
| Orbital Inclination (i) | — |
| Mean Bulk Density | 1.31 g/cm³ (73.1 km/s vesc) |
| Insolation Flux | 59.6537 S⊕ (~81,189 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 65.900 LY (20.210 pc) |