HD 220842 b
Astrophysical Synthesis & Habitability Characterization
HD 220842 b is a confirmed gas giant exoplanet orbiting the star HD 220842, located approximately 210.9 light-years (64.65 parsecs) from the Solar System. First announced in 2016 by Haute-Provence 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 1010.699 Earth masses (3.18 Jupiter masses). Combining its mass and radius yields a mean bulk density of 2.48 g/cm³ (an intermediate density indicative of a deep water-ice mantle or dense volatile envelope), a surface gravity of 5.89 g⊕ (57.76 m/s²), and an escape velocity of 98.3 km/s.
In its orbital architecture around HD 220842, HD 220842 b completes one full revolution every 218.47 Earth days at a semi-major axis of 0.74 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 36.8 km/s (compared to Earth's 29.8 km/s). The planet follows a highly eccentric trajectory (e = 0.404, swinging from 0.441 AU at periapsis out to 1.039 AU at apoapsis), pointing to past dynamical scattering or secular gravitational perturbations.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 398 K (+125°C / +257°F) and receiving 4.16 S⊕ (~5,655 W/m²), HD 220842 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star HD 220842 is classified as a warm F-type star of spectral type F8 with an effective photospheric temperature of 5,960 K, a radius of 1.4165 R☉, a mass of 1.13 M☉, an estimated bolometric luminosity of 2.271 L☉. Stellar evolution modeling indicates a metallicity of [Fe/H] = -0.17 dex (metal-poor relative to the Sun). From Earth, HD 220842 shines at apparent V-band magnitude 7.98 (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 220842 |
| Spectral Type | F8 |
| Effective Temp (Teff) | 5,960 K |
| Stellar Radius | 1.4165 R☉ |
| Stellar Mass | 1.1300 M☉ |
| Bolometric Luminosity | 2.271 L☉ |
| Metallicity [Fe/H] | -0.170 dex |
| Stellar Age | — |
| Apparent Magnitude | V: 7.980 · G: 7.834 |
| System Architecture | 2 Stars, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.740000 AU |
| Orbital Period | 218.47 days |
| Mean Orbital Velocity | 36.8 km/s |
| Orbital Eccentricity (e) | 0.40400 |
| Orbital Inclination (i) | — |
| Mean Bulk Density | 2.48 g/cm³ (98.3 km/s vesc) |
| Insolation Flux | 4.1550 S⊕ (~5,655 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 210.900 LY (64.650 pc) |