HD 12661 b
Astrophysical Synthesis & Habitability Characterization
HD 12661 b is a confirmed gas giant exoplanet orbiting the star HD 12661, located approximately 123.4 light-years (37.85 parsecs) from the Solar System. First announced in 2000 by Multiple Observatories using the Radial Velocity detection technique (measuring periodic Doppler reflex motion in the host star's spectrum), this world measures 13.3 Earth radii (1.19 Jupiter radii) and has a measured mass of 772.327 Earth masses (2.43 Jupiter masses). Combining its mass and radius yields a mean bulk density of 1.81 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 4.37 g⊕ (42.86 m/s²), and an escape velocity of 85.2 km/s.
In its orbital architecture around HD 12661, HD 12661 b completes one full revolution every 262.709 Earth days at a semi-major axis of 0.84 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 34.8 km/s (compared to Earth's 29.8 km/s). The planet follows a highly eccentric trajectory (e = 0.38, swinging from 0.5208 AU at periapsis out to 1.1592 AU at apoapsis), pointing to past dynamical scattering or secular gravitational perturbations.
☁️ Atmospheric Regime (Volatile / Gas Envelope): With a radius of 13.300 R⊕, HD 12661 b exceeds the empirical ~1.8–2.2 R⊕ Fulton radius valley threshold, indicating a substantial hydrogen-helium or supercritical volatile envelope without a conventional solid terrestrial surface.
The host star HD 12661 is classified as an orange K-type star of spectral type K0 with an effective photospheric temperature of 5,645 K, a radius of 1.2 R☉, a mass of 1.2 M☉, an estimated bolometric luminosity of 1.312 L☉. Stellar evolution modeling indicates an estimated stellar age of 6.39 Gyr and a metallicity of [Fe/H] = 0.36 dex (metal-rich relative to the Sun). From Earth, HD 12661 shines at apparent V-band magnitude 7.43 (accessible to binoculars and small amateur telescopes) in the Northern celestial hemisphere. The HD 12661 system is a multi-planet architecture hosting 2 confirmed worlds, with HD 12661 b sharing its stellar neighborhood alongside HD 12661 c.
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: Multiple Observatories · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | HD 12661 |
| Spectral Type | K0 |
| Effective Temp (Teff) | 5,645 K |
| Stellar Radius | 1.2000 R☉ |
| Stellar Mass | 1.2000 M☉ |
| Bolometric Luminosity | 1.312 L☉ |
| Metallicity [Fe/H] | 0.360 dex |
| Stellar Age | 6.390 Gyr |
| Apparent Magnitude | V: 7.430 · G: 7.247 |
| System Architecture | 1 Star, 2 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.840000 AU |
| Orbital Period | 262.709 days |
| Mean Orbital Velocity | 34.8 km/s |
| Orbital Eccentricity (e) | 0.38000 |
| Orbital Inclination (i) | 86.0000° |
| Mean Bulk Density | 1.81 g/cm³ (85.2 km/s vesc) |
| Insolation Flux | 1.9237 S⊕ (~2,618 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 123.400 LY (37.848 pc) |