Kepler-166 c
Astrophysical Synthesis & Habitability Characterization
Kepler-166 c is a confirmed sub-neptune exoplanet orbiting the star Kepler-166, located approximately 1968.4 light-years (603.53 parsecs) from the Solar System. First announced in 2014 by Kepler using the Transit detection technique (producing an estimated primary transit depth of 0.0865% across the stellar disk), this world measures 2.38 Earth radii and has a measured mass of 6.26 Earth masses. Combining its mass and radius yields a mean bulk density of 2.56 g/cm³ (an intermediate density indicative of a deep water-ice mantle or dense volatile envelope), a surface gravity of 1.11 g⊕ (10.89 m/s²), and an escape velocity of 18.1 km/s.
In its orbital architecture around Kepler-166, Kepler-166 c completes one full revolution every 34.26 Earth days at a semi-major axis of 0.195 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 61.9 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 468 K (+195°C / +383°F) and receiving 10.51 S⊕ (~14,300 W/m²), Kepler-166 c orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star Kepler-166 is classified as a stellar host with an effective photospheric temperature of 5,413 K, a radius of 0.742 R☉, a mass of 0.811 M☉, an estimated bolometric luminosity of 0.424 L☉. Stellar evolution modeling indicates an estimated stellar age of 5.01 Gyr and a metallicity of [Fe/H] = -0.08 dex (near-solar heavy-element abundance). From Earth, Kepler-166 shines at apparent V-band magnitude 14.857 (faint and requiring research-grade or CCD telescopic photometry) in the Northern celestial hemisphere. The Kepler-166 system is a multi-planet architecture hosting 3 confirmed worlds, with Kepler-166 c sharing its stellar neighborhood alongside Kepler-166 d, Kepler-166 b.
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-166 |
| Spectral Type | Unclassified |
| Effective Temp (Teff) | 5,413 K |
| Stellar Radius | 0.7420 R☉ |
| Stellar Mass | 0.8110 M☉ |
| Bolometric Luminosity | 0.424 L☉ |
| Metallicity [Fe/H] | -0.080 dex |
| Stellar Age | 5.010 Gyr |
| Apparent Magnitude | V: 14.857 · G: 14.685 |
| System Architecture | 1 Star, 3 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.195000 AU |
| Orbital Period | 34.26 days |
| Mean Orbital Velocity | 61.9 km/s |
| Orbital Eccentricity (e) | 0.00000 |
| Orbital Inclination (i) | 89.9900° |
| Mean Bulk Density | 2.56 g/cm³ (18.1 km/s vesc) |
| Insolation Flux | 10.5070 S⊕ (~14,300 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 1968.400 LY (603.530 pc) |