HD 177565 b
Astrophysical Synthesis & Habitability Characterization
HD 177565 b is a confirmed sub-neptune exoplanet orbiting the star HD 177565, located approximately 55.2 light-years (16.92 parsecs) from the Solar System. First announced in 2017 by La Silla Observatory using the Radial Velocity detection technique (measuring periodic Doppler reflex motion in the host star's spectrum), this world measures 4 Earth radii (0.36 Jupiter radii) and has a measured mass of 15.1 Earth masses. Combining its mass and radius yields a mean bulk density of 1.3 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 0.94 g⊕ (9.22 m/s²), and an escape velocity of 21.7 km/s.
In its orbital architecture around HD 177565, HD 177565 b completes one full revolution every 44.505 Earth days at a semi-major axis of 0.246 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 60.1 km/s (compared to Earth's 29.8 km/s). Its moderate orbital eccentricity of e = 0.0593 carries the world between 0.2314 AU at periapsis and 0.2606 AU at apoapsis, driving measurable seasonal insolation cycles.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 539 K (+266°C / +511°F) and receiving 14.59 S⊕ (~19,863 W/m²), HD 177565 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star HD 177565 is classified as a solar-type yellow star of spectral type G8V with an effective photospheric temperature of 5,627 K, a radius of 0.9715 R☉, a mass of 1 M☉, an estimated bolometric luminosity of 0.849 L☉. Stellar evolution modeling indicates an estimated stellar age of 6.88 Gyr and a metallicity of [Fe/H] = 0.081 dex (metal-rich relative to the Sun). From Earth, HD 177565 shines at apparent V-band magnitude 6.15 (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: La Silla Observatory · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | HD 177565 |
| Spectral Type | G8V |
| Effective Temp (Teff) | 5,627 K |
| Stellar Radius | 0.9715 R☉ |
| Stellar Mass | 1.0000 M☉ |
| Bolometric Luminosity | 0.849 L☉ |
| Metallicity [Fe/H] | 0.081 dex |
| Stellar Age | 6.880 Gyr |
| Apparent Magnitude | V: 6.150 · G: 5.974 |
| System Architecture | 1 Star, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.246000 AU |
| Orbital Period | 44.505 days |
| Mean Orbital Velocity | 60.1 km/s |
| Orbital Eccentricity (e) | 0.05930 |
| Orbital Inclination (i) | — |
| Mean Bulk Density | 1.3 g/cm³ (21.7 km/s vesc) |
| Insolation Flux | 14.5941 S⊕ (~19,863 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 55.200 LY (16.918 pc) |