Kepler-178 c
Astrophysical Synthesis & Habitability Characterization
Kepler-178 c 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 0.0613% across the stellar disk), this world measures 2.88 Earth radii and has a measured mass of 8.65 Earth masses. Combining its mass and radius yields a mean bulk density of 2 g/cm³ (an intermediate density indicative of a deep water-ice mantle or dense volatile envelope), a surface gravity of 1.04 g⊕ (10.2 m/s²), and an escape velocity of 19.4 km/s.
In its orbital architecture around Kepler-178, Kepler-178 c completes one full revolution every 20.553 Earth days at a semi-major axis of 0.142 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 75.2 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 656 K (+383°C / +721°F) and receiving 30.55 S⊕ (~41,573 W/m²), Kepler-178 c 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 c sharing its stellar neighborhood alongside Kepler-178 b, Kepler-178 d.
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) | 0.142000 AU |
| Orbital Period | 20.553 days |
| Mean Orbital Velocity | 75.2 km/s |
| Orbital Eccentricity (e) | 0.00000 |
| Orbital Inclination (i) | 89.4700° |
| Mean Bulk Density | 2 g/cm³ (19.4 km/s vesc) |
| Insolation Flux | 30.5460 S⊕ (~41,573 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 2335.400 LY (716.025 pc) |