HD 217958 b
Astrophysical Synthesis & Habitability Characterization
HD 217958 b is a confirmed gas giant exoplanet orbiting the star HD 217958, located approximately 201.6 light-years (61.8 parsecs) from the Solar System. First announced in 2022 by Multiple Observatories using the Radial Velocity detection technique (measuring periodic Doppler reflex motion in the host star's spectrum), this world measures 14.2 Earth radii (1.27 Jupiter radii) and has a measured mass of 166.542 Earth masses (0.52 Jupiter masses). Combining its mass and radius yields a mean bulk density of 0.32 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 0.83 g⊕ (8.14 m/s²), and an escape velocity of 38.3 km/s.
In its orbital architecture around HD 217958, HD 217958 b completes one full revolution every 2560.198 Earth days (7.01Julian years) at a semi-major axis of 3.758 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 16 km/s (compared to Earth's 29.8 km/s). Its moderate orbital eccentricity of e = 0.156 carries the world between 3.1718 AU at periapsis and 4.3442 AU at apoapsis, driving measurable seasonal insolation cycles.
❄️ Thermal Regime (Cryogenic Zone): With an equilibrium temperature of 170 K (-103°C / -153°F) and an incident flux of 0.14 S⊕ (~189 W/m²), surface water and volatile species on HD 217958 b would remain locked in cryogenic ice phases unless warmed by subsurface tidal or radiogenic heating.
The host star HD 217958 is classified as a stellar host with an effective photospheric temperature of 5,931 K, a radius of 1.3262 R☉, a mass of 1.08 M☉, an estimated bolometric luminosity of 1.953 L☉. Stellar evolution modeling indicates a metallicity of [Fe/H] = 0.287 dex (metal-rich relative to the Sun). From Earth, HD 217958 shines at apparent V-band magnitude 8.05 (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: Multiple Observatories · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | HD 217958 |
| Spectral Type | Unclassified |
| Effective Temp (Teff) | 5,931 K |
| Stellar Radius | 1.3262 R☉ |
| Stellar Mass | 1.0800 M☉ |
| Bolometric Luminosity | 1.953 L☉ |
| Metallicity [Fe/H] | 0.287 dex |
| Stellar Age | — |
| Apparent Magnitude | V: 8.050 · G: 7.895 |
| System Architecture | 1 Star, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 3.758000 AU |
| Orbital Period | 2560.198 days |
| Mean Orbital Velocity | 16 km/s |
| Orbital Eccentricity (e) | 0.15600 |
| Orbital Inclination (i) | 91.3570° |
| Mean Bulk Density | 0.32 g/cm³ (38.3 km/s vesc) |
| Insolation Flux | 0.1388 S⊕ (~189 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 201.600 LY (61.796 pc) |