HD 16417 b
Astrophysical Synthesis & Habitability Characterization
HD 16417 b is a confirmed sub-neptune exoplanet orbiting the star HD 16417, located approximately 82.8 light-years (25.39 parsecs) from the Solar System. First announced in 2008 by Anglo-Australian Telescope using the Radial Velocity detection technique (measuring periodic Doppler reflex motion in the host star's spectrum), this world measures 5 Earth radii (0.45 Jupiter radii) and has a measured mass of 22.1 Earth masses. Combining its mass and radius yields a mean bulk density of 0.97 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 0.88 g⊕ (8.63 m/s²), and an escape velocity of 23.5 km/s.
In its orbital architecture around HD 16417, HD 16417 b completes one full revolution every 17.24 Earth days at a semi-major axis of 0.14 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 88.3 km/s (compared to Earth's 29.8 km/s). Its moderate orbital eccentricity of e = 0.2 carries the world between 0.112 AU at periapsis and 0.168 AU at apoapsis, driving measurable seasonal insolation cycles.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 964 K (+691°C / +1276°F) and receiving 141.55 S⊕ (~192,651 W/m²), HD 16417 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star HD 16417 is classified as a solar-type yellow star of spectral type G1 V with an effective photospheric temperature of 5,841 K, a radius of 1.64 R☉, a mass of 1.2 M☉, an estimated bolometric luminosity of 2.809 L☉. Stellar evolution modeling indicates an estimated stellar age of 7 Gyr and a metallicity of [Fe/H] = 0.06 dex (metal-rich relative to the Sun). From Earth, HD 16417 shines at apparent V-band magnitude 5.78 (visible to the unaided human eye under dark skies) 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: Anglo-Australian Telescope · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | HD 16417 |
| Spectral Type | G1 V |
| Effective Temp (Teff) | 5,841 K |
| Stellar Radius | 1.6400 R☉ |
| Stellar Mass | 1.2000 M☉ |
| Bolometric Luminosity | 2.809 L☉ |
| Metallicity [Fe/H] | 0.060 dex |
| Stellar Age | 7.000 Gyr |
| Apparent Magnitude | V: 5.780 · G: 5.613 |
| System Architecture | 2 Stars, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.140000 AU |
| Orbital Period | 17.24 days |
| Mean Orbital Velocity | 88.3 km/s |
| Orbital Eccentricity (e) | 0.20000 |
| Orbital Inclination (i) | — |
| Mean Bulk Density | 0.97 g/cm³ (23.5 km/s vesc) |
| Insolation Flux | 141.5514 S⊕ (~192,651 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 82.800 LY (25.394 pc) |