HD 217107 b
Astrophysical Synthesis & Habitability Characterization
HD 217107 b is a confirmed gas giant exoplanet orbiting the star HD 217107, located approximately 65.4 light-years (20.06 parsecs) from the Solar System. First announced in 1998 by Lick 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 459.58 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 2.48 g⊕ (24.32 m/s²), and an escape velocity of 65 km/s.
In its orbital architecture around HD 217107, HD 217107 b completes one full revolution every 7.127 Earth days at a semi-major axis of 0.07359 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 112.3 km/s (compared to Earth's 29.8 km/s). Its moderate orbital eccentricity of e = 0.1284 carries the world between 0.0641 AU at periapsis and 0.083 AU at apoapsis, driving measurable seasonal insolation cycles.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 1106 K (+833°C / +1531°F) and receiving 231.15 S⊕ (~314,601 W/m²), HD 217107 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star HD 217107 is classified as a solar-type yellow star of spectral type G with an effective photospheric temperature of 5,622 K, a radius of 1.2245 R☉, a mass of 1.045 M☉, an estimated bolometric luminosity of 1.344 L☉. Stellar evolution modeling indicates an estimated stellar age of 11.9 Gyr and a metallicity of [Fe/H] = 0.37 dex (metal-rich relative to the Sun). From Earth, HD 217107 shines at apparent V-band magnitude 6.155 (visible to the unaided human eye under dark skies) in the Southern celestial hemisphere. The HD 217107 system is a multi-planet architecture hosting 2 confirmed worlds, with HD 217107 b sharing its stellar neighborhood alongside HD 217107 c.
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: Lick Observatory · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | HD 217107 |
| Spectral Type | G |
| Effective Temp (Teff) | 5,622 K |
| Stellar Radius | 1.2245 R☉ |
| Stellar Mass | 1.0450 M☉ |
| Bolometric Luminosity | 1.344 L☉ |
| Metallicity [Fe/H] | 0.370 dex |
| Stellar Age | 11.900 Gyr |
| Apparent Magnitude | V: 6.155 · G: 5.964 |
| System Architecture | 1 Star, 2 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.073590 AU |
| Orbital Period | 7.127 days |
| Mean Orbital Velocity | 112.3 km/s |
| Orbital Eccentricity (e) | 0.12840 |
| Orbital Inclination (i) | 93.0000° |
| Mean Bulk Density | 1.01 g/cm³ (65 km/s vesc) |
| Insolation Flux | 231.1546 S⊕ (~314,601 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 65.400 LY (20.062 pc) |