Kepler-1666 c
Astrophysical Synthesis & Habitability Characterization
Kepler-1666 c is a confirmed sub-neptune exoplanet orbiting the star Kepler-1666, located approximately 4498.9 light-years (1379.37 parsecs) from the Solar System. First announced in 2020 by Kepler using the Transit detection technique (producing an estimated primary transit depth of 0.067% across the stellar disk), this world measures 3.236 Earth radii (0.29 Jupiter radii) and has a measured mass of 10.5 Earth masses. Combining its mass and radius yields a mean bulk density of 1.71 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 1 g⊕ (9.81 m/s²), and an escape velocity of 20.1 km/s.
In its orbital architecture around Kepler-1666, Kepler-1666 c completes one full revolution every 40.716 Earth days at a semi-major axis of 0.2383 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 63.7 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 578 K (+305°C / +581°F) and receiving 26.34 S⊕ (~35,849 W/m²), Kepler-1666 c orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star Kepler-1666 is classified as a stellar host with an effective photospheric temperature of 6,293 K, a radius of 1.1459 R☉, a mass of 1.23 M☉, an estimated bolometric luminosity of 1.848 L☉. Stellar evolution modeling indicates an estimated stellar age of 0.41 Gyr and a metallicity of [Fe/H] = -0.2 dex (metal-poor relative to the Sun). From Earth, Kepler-1666 shines at apparent V-band magnitude 15.104 (faint and requiring research-grade or CCD telescopic photometry) in the Northern celestial hemisphere. The Kepler-1666 system is a multi-planet architecture hosting 2 confirmed worlds, with Kepler-1666 c sharing its stellar neighborhood alongside Kepler-1666 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-1666 |
| Spectral Type | Unclassified |
| Effective Temp (Teff) | 6,293 K |
| Stellar Radius | 1.1459 R☉ |
| Stellar Mass | 1.2300 M☉ |
| Bolometric Luminosity | 1.848 L☉ |
| Metallicity [Fe/H] | -0.200 dex |
| Stellar Age | 0.410 Gyr |
| Apparent Magnitude | V: 15.104 · G: 15.015 |
| System Architecture | 1 Star, 2 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.238300 AU |
| Orbital Period | 40.716 days |
| Mean Orbital Velocity | 63.7 km/s |
| Orbital Eccentricity (e) | 0.00000 |
| Orbital Inclination (i) | 89.9900° |
| Mean Bulk Density | 1.71 g/cm³ (20.1 km/s vesc) |
| Insolation Flux | 26.3400 S⊕ (~35,849 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 4498.900 LY (1379.370 pc) |