HD 221420 b
Astrophysical Synthesis & Habitability Characterization
HD 221420 b is a confirmed gas giant exoplanet orbiting the star HD 221420, located approximately 101.6 light-years (31.14 parsecs) from the Solar System. First announced in 2019 by Anglo-Australian Telescope using the Radial Velocity detection technique (measuring periodic Doppler reflex motion in the host star's spectrum), this world measures 12 Earth radii (1.07 Jupiter radii) and has a measured mass of 7278.271 Earth masses (22.9 Jupiter masses). Combining its mass and radius yields a mean bulk density of 23.22 g/cm³ (an iron-enriched, high-compression rocky core), a surface gravity of 50.54 g⊕ (495.63 m/s²), and an escape velocity of 275.5 km/s.
In its orbital architecture around HD 221420, HD 221420 b completes one full revolution every 10090 Earth days (27.62Julian years) at a semi-major axis of 10.15 AU (a wide outer-system orbit beyond Jupiter's 5.20 AU distance in our Solar System). Its mean orbital velocity is approximately 10.9 km/s (compared to Earth's 29.8 km/s). Its moderate orbital eccentricity of e = 0.14 carries the world between 8.729 AU at periapsis and 11.571 AU at apoapsis, driving measurable seasonal insolation cycles.
❄️ Thermal Regime (Cryogenic Zone): With an equilibrium temperature of 123 K (-150°C / -238°F) and an incident flux of 0.04 S⊕ (~53 W/m²), surface water and volatile species on HD 221420 b would remain locked in cryogenic ice phases unless warmed by subsurface tidal or radiogenic heating.
The host star HD 221420 is classified as a solar-type yellow star of spectral type G2 IV-V with an effective photospheric temperature of 5,847 K, a radius of 1.947 R☉, a mass of 1.351 M☉, an estimated bolometric luminosity of 3.975 L☉. Stellar evolution modeling indicates an estimated stellar age of 3.65 Gyr and a metallicity of [Fe/H] = 0.33 dex (metal-rich relative to the Sun). From Earth, HD 221420 shines at apparent V-band magnitude 5.82 (visible to the unaided human eye under dark skies) 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: Anglo-Australian Telescope · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | HD 221420 |
| Spectral Type | G2 IV-V |
| Effective Temp (Teff) | 5,847 K |
| Stellar Radius | 1.9470 R☉ |
| Stellar Mass | 1.3510 M☉ |
| Bolometric Luminosity | 3.975 L☉ |
| Metallicity [Fe/H] | 0.330 dex |
| Stellar Age | 3.650 Gyr |
| Apparent Magnitude | V: 5.820 · G: 5.659 |
| System Architecture | 1 Star, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 10.150000 AU |
| Orbital Period | 10090 days |
| Mean Orbital Velocity | 10.9 km/s |
| Orbital Eccentricity (e) | 0.14000 |
| Orbital Inclination (i) | 164.0000° |
| Mean Bulk Density | 23.22 g/cm³ (275.5 km/s vesc) |
| Insolation Flux | 0.0389 S⊕ (~53 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 101.600 LY (31.142 pc) |