HD 4917 b
Astrophysical Synthesis & Habitability Characterization
HD 4917 b is a confirmed gas giant exoplanet orbiting the star HD 4917, located approximately 666.3 light-years (204.28 parsecs) from the Solar System. First announced in 2018 by W. M. Keck Observatory using the Radial Velocity detection technique (measuring periodic Doppler reflex motion in the host star's spectrum), this world measures 13.5 Earth radii (1.2 Jupiter radii) and has a measured mass of 513.295 Earth masses (1.61 Jupiter masses). Combining its mass and radius yields a mean bulk density of 1.15 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 2.82 g⊕ (27.65 m/s²), and an escape velocity of 69 km/s.
In its orbital architecture around HD 4917, HD 4917 b completes one full revolution every 400.5 Earth days (1.1Julian years) at a semi-major axis of 1.167 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 31.7 km/s (compared to Earth's 29.8 km/s). Its moderate orbital eccentricity of e = 0.066 carries the world between 1.09 AU at periapsis and 1.244 AU at apoapsis, driving measurable seasonal insolation cycles.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 480 K (+207°C / +405°F) and receiving 20.98 S⊕ (~28,551 W/m²), HD 4917 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star HD 4917 is classified as an orange K-type star of spectral type K0 III/IV with an effective photospheric temperature of 4,802 K, a radius of 5.01 R☉, a mass of 1.32 M☉, an estimated bolometric luminosity of 11.974 L☉. Stellar evolution modeling indicates a metallicity of [Fe/H] = 0.18 dex (metal-rich relative to the Sun). From Earth, HD 4917 shines at apparent V-band magnitude 8.03 (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: W. M. Keck Observatory · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | HD 4917 |
| Spectral Type | K0 III/IV |
| Effective Temp (Teff) | 4,802 K |
| Stellar Radius | 5.0100 R☉ |
| Stellar Mass | 1.3200 M☉ |
| Bolometric Luminosity | 11.974 L☉ |
| Metallicity [Fe/H] | 0.180 dex |
| Stellar Age | — |
| Apparent Magnitude | V: 8.030 · G: 7.749 |
| System Architecture | 1 Star, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 1.167000 AU |
| Orbital Period | 400.5 days |
| Mean Orbital Velocity | 31.7 km/s |
| Orbital Eccentricity (e) | 0.06600 |
| Orbital Inclination (i) | — |
| Mean Bulk Density | 1.15 g/cm³ (69 km/s vesc) |
| Insolation Flux | 20.9781 S⊕ (~28,551 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 666.300 LY (204.277 pc) |