Kepler-176 d
Astrophysical Synthesis & Habitability Characterization
Kepler-176 d is a confirmed sub-neptune exoplanet orbiting the star Kepler-176, located approximately 1719.9 light-years (527.32 parsecs) from the Solar System. First announced in 2014 by Kepler using the Transit detection technique (producing an estimated primary transit depth of 0.0667% across the stellar disk), this world measures 2.51 Earth radii and has a measured mass of 1.72 Earth masses. Combining its mass and radius yields a mean bulk density of 0.6 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 0.27 g⊕ (2.65 m/s²), and an escape velocity of 9.3 km/s.
In its orbital architecture around Kepler-176, Kepler-176 d completes one full revolution every 25.752 Earth days at a semi-major axis of 0.163 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 68.9 km/s (compared to Earth's 29.8 km/s). The orbit is modeled as circular (e = 0.00), maintaining a constant stellar distance throughout its year.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 501 K (+228°C / +442°F) and receiving 15.54 S⊕ (~21,144 W/m²), Kepler-176 d orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star Kepler-176 is classified as a stellar host with an effective photospheric temperature of 5,232 K, a radius of 0.891 R☉, a mass of 0.86 M☉, an estimated bolometric luminosity of 0.534 L☉. Stellar evolution modeling indicates an estimated stellar age of 2.45 Gyr and a metallicity of [Fe/H] = 0.13 dex (metal-rich relative to the Sun). From Earth, Kepler-176 shines at apparent V-band magnitude 14.767 (faint and requiring research-grade or CCD telescopic photometry) in the Northern celestial hemisphere. The Kepler-176 system is a multi-planet architecture hosting 4 confirmed worlds, with Kepler-176 d sharing its stellar neighborhood alongside Kepler-176 b, Kepler-176 c, Kepler-176 e.
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: Kepler · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | Kepler-176 |
| Spectral Type | Unclassified |
| Effective Temp (Teff) | 5,232 K |
| Stellar Radius | 0.8910 R☉ |
| Stellar Mass | 0.8600 M☉ |
| Bolometric Luminosity | 0.534 L☉ |
| Metallicity [Fe/H] | 0.130 dex |
| Stellar Age | 2.450 Gyr |
| Apparent Magnitude | V: 14.767 · G: 14.545 |
| System Architecture | 1 Star, 4 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.163000 AU |
| Orbital Period | 25.752 days |
| Mean Orbital Velocity | 68.9 km/s |
| Orbital Eccentricity (e) | 0.00000 |
| Orbital Inclination (i) | 89.5300° |
| Mean Bulk Density | 0.6 g/cm³ (9.3 km/s vesc) |
| Insolation Flux | 15.5360 S⊕ (~21,144 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 1719.900 LY (527.321 pc) |