HD 22781 b
Astrophysical Synthesis & Habitability Characterization
HD 22781 b is a confirmed gas giant exoplanet orbiting the star HD 22781, located approximately 106.3 light-years (32.6 parsecs) from the Solar System. First announced in 2011 by Haute-Provence Observatory using the Radial Velocity detection technique (measuring periodic Doppler reflex motion in the host star's spectrum), this world measures 12.3 Earth radii (1.1 Jupiter radii) and has a measured mass of 4338.2 Earth masses (13.65 Jupiter masses). Combining its mass and radius yields a mean bulk density of 12.85 g/cm³ (an iron-enriched, high-compression rocky core), a surface gravity of 28.67 g⊕ (281.16 m/s²), and an escape velocity of 210.1 km/s.
In its orbital architecture around HD 22781, HD 22781 b completes one full revolution every 528.07 Earth days (1.45Julian years) at a semi-major axis of 1.167 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 24 km/s (compared to Earth's 29.8 km/s). The planet follows a highly eccentric trajectory (e = 0.8191, swinging from 0.2111 AU at periapsis out to 2.1229 AU at apoapsis), pointing to past dynamical scattering or secular gravitational perturbations.
☁️ Atmospheric Regime (Volatile / Gas Envelope): With a radius of 12.300 R⊕, HD 22781 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 22781 is classified as an orange K-type star of spectral type K1 with an effective photospheric temperature of 5,027 K, a radius of 0.7435 R☉, a mass of 0.75 M☉, an estimated bolometric luminosity of 0.317 L☉. Stellar evolution modeling indicates an estimated stellar age of 4.8 Gyr and a metallicity of [Fe/H] = -0.37 dex (metal-poor relative to the Sun). From Earth, HD 22781 shines at apparent V-band magnitude 8.78 (accessible to binoculars and small amateur telescopes) 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: Haute-Provence Observatory · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | HD 22781 |
| Spectral Type | K1 |
| Effective Temp (Teff) | 5,027 K |
| Stellar Radius | 0.7435 R☉ |
| Stellar Mass | 0.7500 M☉ |
| Bolometric Luminosity | 0.317 L☉ |
| Metallicity [Fe/H] | -0.370 dex |
| Stellar Age | 4.800 Gyr |
| Apparent Magnitude | V: 8.780 · G: 8.524 |
| System Architecture | 1 Star, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 1.167000 AU |
| Orbital Period | 528.07 days |
| Mean Orbital Velocity | 24 km/s |
| Orbital Eccentricity (e) | 0.81910 |
| Orbital Inclination (i) | — |
| Mean Bulk Density | 12.85 g/cm³ (210.1 km/s vesc) |
| Insolation Flux | 0.2456 S⊕ (~334 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 106.300 LY (32.603 pc) |