HD 221287 b
Astrophysical Synthesis & Habitability Characterization
HD 221287 b is a confirmed gas giant exoplanet orbiting the star HD 221287, located approximately 182.4 light-years (55.92 parsecs) from the Solar System. First announced in 2007 by La Silla Observatory using the Radial Velocity detection technique (measuring periodic Doppler reflex motion in the host star's spectrum), this world measures 13.1 Earth radii (1.17 Jupiter radii) and has a measured mass of 982.05 Earth masses (3.09 Jupiter masses). Combining its mass and radius yields a mean bulk density of 2.41 g/cm³ (an intermediate density indicative of a deep water-ice mantle or dense volatile envelope), a surface gravity of 5.72 g⊕ (56.09 m/s²), and an escape velocity of 96.9 km/s.
In its orbital architecture around HD 221287, HD 221287 b completes one full revolution every 456.1 Earth days (1.25Julian years) at a semi-major axis of 1.25 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 29.8 km/s (compared to Earth's 29.8 km/s). Its moderate orbital eccentricity of e = 0.08 carries the world between 1.15 AU at periapsis and 1.35 AU at apoapsis, driving measurable seasonal insolation cycles.
☁️ Atmospheric Regime (Volatile / Gas Envelope): With a radius of 13.100 R⊕, HD 221287 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 221287 is classified as a warm F-type star of spectral type F7 V with an effective photospheric temperature of 6,304 K, a radius of 1.1386 R☉, a mass of 1.25 M☉, an estimated bolometric luminosity of 1.837 L☉. Stellar evolution modeling indicates an estimated stellar age of 1.3 Gyr and a metallicity of [Fe/H] = -0.03 dex (near-solar heavy-element abundance). From Earth, HD 221287 shines at apparent V-band magnitude 7.82 (accessible to binoculars and small amateur telescopes) in the Southern 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: La Silla Observatory · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | HD 221287 |
| Spectral Type | F7 V |
| Effective Temp (Teff) | 6,304 K |
| Stellar Radius | 1.1386 R☉ |
| Stellar Mass | 1.2500 M☉ |
| Bolometric Luminosity | 1.837 L☉ |
| Metallicity [Fe/H] | -0.030 dex |
| Stellar Age | 1.300 Gyr |
| Apparent Magnitude | V: 7.820 · G: 7.682 |
| System Architecture | 1 Star, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 1.250000 AU |
| Orbital Period | 456.1 days |
| Mean Orbital Velocity | 29.8 km/s |
| Orbital Eccentricity (e) | 0.08000 |
| Orbital Inclination (i) | — |
| Mean Bulk Density | 2.41 g/cm³ (96.9 km/s vesc) |
| Insolation Flux | 1.0624 S⊕ (~1,446 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 182.400 LY (55.923 pc) |