Kepler-178 d
Astrophysical Synthesis & Habitability Characterization
Kepler-178 d is a confirmed sub-neptune exoplanet orbiting the star Kepler-178, located approximately 2335.4 light-years (716.03 parsecs) from the Solar System. First announced in 2014 by Kepler using the Transit detection technique (producing an estimated primary transit depth of 0.1154% across the stellar disk), this world measures 3.95 Earth radii (0.35 Jupiter radii) and has a measured mass of 14.8 Earth masses. Combining its mass and radius yields a mean bulk density of 1.32 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 0.95 g⊕ (9.32 m/s²), and an escape velocity of 21.7 km/s.
In its orbital architecture around Kepler-178, Kepler-178 d completes one full revolution every 96.679 Earth days at a semi-major axis of 0.397 AU (situated at an orbital separation between Mercury's 0.39 AU and Venus's 0.72 AU). Its mean orbital velocity is approximately 44.7 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 392 K (+119°C / +246°F) and receiving 3.87 S⊕ (~5,273 W/m²), Kepler-178 d orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star Kepler-178 is classified as a stellar host with an effective photospheric temperature of 5,676 K, a radius of 1.066 R☉, a mass of 0.852 M☉, an estimated bolometric luminosity of 1.058 L☉. Stellar evolution modeling indicates an estimated stellar age of 9.12 Gyr and a metallicity of [Fe/H] = -0.04 dex (near-solar heavy-element abundance). From Earth, Kepler-178 shines at apparent V-band magnitude 14.876 (faint and requiring research-grade or CCD telescopic photometry) in the Northern celestial hemisphere. The Kepler-178 system is a multi-planet architecture hosting 3 confirmed worlds, with Kepler-178 d sharing its stellar neighborhood alongside Kepler-178 b, Kepler-178 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: Kepler · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | Kepler-178 |
| Spectral Type | Unclassified |
| Effective Temp (Teff) | 5,676 K |
| Stellar Radius | 1.0660 R☉ |
| Stellar Mass | 0.8520 M☉ |
| Bolometric Luminosity | 1.058 L☉ |
| Metallicity [Fe/H] | -0.040 dex |
| Stellar Age | 9.120 Gyr |
| Apparent Magnitude | V: 14.876 · G: 14.578 |
| System Architecture | 1 Star, 3 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.397000 AU |
| Orbital Period | 96.679 days |
| Mean Orbital Velocity | 44.7 km/s |
| Orbital Eccentricity (e) | 0.00000 |
| Orbital Inclination (i) | 89.8500° |
| Mean Bulk Density | 1.32 g/cm³ (21.7 km/s vesc) |
| Insolation Flux | 3.8740 S⊕ (~5,273 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 2335.400 LY (716.025 pc) |