HD 220773 b
Astrophysical Synthesis & Habitability Characterization
HD 220773 b is a confirmed gas giant exoplanet orbiting the star HD 220773, located approximately 164.7 light-years (50.51 parsecs) from the Solar System. First announced in 2011 by McDonald Observatory using the Radial Velocity detection technique (measuring periodic Doppler reflex motion in the host star's spectrum), this world measures 13.6 Earth radii (1.21 Jupiter radii) and has a measured mass of 460.8 Earth masses (1.45 Jupiter masses). Combining its mass and radius yields a mean bulk density of 1.01 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 2.49 g⊕ (24.42 m/s²), and an escape velocity of 65.1 km/s.
In its orbital architecture around HD 220773, HD 220773 b completes one full revolution every 3724.7 Earth days (10.2Julian years) at a semi-major axis of 4.94 AU (corresponding to the middle-system regime between Mars at 1.52 AU and Jupiter at 5.20 AU). Its mean orbital velocity is approximately 14.4 km/s (compared to Earth's 29.8 km/s). The planet follows a highly eccentric trajectory (e = 0.51, swinging from 2.4206 AU at periapsis out to 7.4594 AU at apoapsis), pointing to past dynamical scattering or secular gravitational perturbations.
❄️ Thermal Regime (Cryogenic Zone): With an equilibrium temperature of 167 K (-106°C / -159°F) and an incident flux of 0.13 S⊕ (~176 W/m²), surface water and volatile species on HD 220773 b would remain locked in cryogenic ice phases unless warmed by subsurface tidal or radiogenic heating.
The host star HD 220773 is classified as a warm F-type star of spectral type F9 with an effective photospheric temperature of 5,940 K, a radius of 1.6797 R☉, a mass of 1.16 M☉, an estimated bolometric luminosity of 3.151 L☉. Stellar evolution modeling indicates an estimated stellar age of 4.4 Gyr and a metallicity of [Fe/H] = 0.09 dex (metal-rich relative to the Sun). From Earth, HD 220773 shines at apparent V-band magnitude 7.108 (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: McDonald Observatory · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | HD 220773 |
| Spectral Type | F9 |
| Effective Temp (Teff) | 5,940 K |
| Stellar Radius | 1.6797 R☉ |
| Stellar Mass | 1.1600 M☉ |
| Bolometric Luminosity | 3.151 L☉ |
| Metallicity [Fe/H] | 0.090 dex |
| Stellar Age | 4.400 Gyr |
| Apparent Magnitude | V: 7.108 · G: 6.946 |
| System Architecture | 1 Star, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 4.940000 AU |
| Orbital Period | 3724.7 days |
| Mean Orbital Velocity | 14.4 km/s |
| Orbital Eccentricity (e) | 0.51000 |
| Orbital Inclination (i) | — |
| Mean Bulk Density | 1.01 g/cm³ (65.1 km/s vesc) |
| Insolation Flux | 0.1290 S⊕ (~176 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 164.700 LY (50.510 pc) |