K2-166 b
Astrophysical Synthesis & Habitability Characterization
K2-166 b is a confirmed sub-neptune exoplanet orbiting the star K2-166, located approximately 1555.4 light-years (476.88 parsecs) from the Solar System. First announced in 2018 by K2 using the Transit detection technique (producing an estimated primary transit depth of 0.0156% across the stellar disk), this world measures 2.19 Earth radii and has a measured mass of 5.43 Earth masses. Combining its mass and radius yields a mean bulk density of 2.85 g/cm³ (an intermediate density indicative of a deep water-ice mantle or dense volatile envelope), a surface gravity of 1.13 g⊕ (11.08 m/s²), and an escape velocity of 17.6 km/s.
In its orbital architecture around K2-166, K2-166 b completes one full revolution every 8.527 Earth days at a semi-major axis of 0.0858 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 109.5 km/s (compared to Earth's 29.8 km/s).
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 1140 K (+867°C / +1593°F) and receiving 390.40 S⊕ (~531,328 W/m²), K2-166 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star K2-166 is classified as a stellar host with an effective photospheric temperature of 5,960 K, a radius of 1.61 R☉, a mass of 1.16 M☉, an estimated bolometric luminosity of 2.934 L☉. Stellar evolution modeling indicates a metallicity of [Fe/H] = 0.09 dex (metal-rich relative to the Sun). From Earth, K2-166 shines at apparent V-band magnitude 12.081 (faint and requiring research-grade or CCD telescopic photometry) in the Northern celestial hemisphere. The K2-166 system is a multi-planet architecture hosting 2 confirmed worlds, with K2-166 b sharing its stellar neighborhood alongside EPIC 201615463 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: K2 · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | K2-166 |
| Spectral Type | Unclassified |
| Effective Temp (Teff) | 5,960 K |
| Stellar Radius | 1.6100 R☉ |
| Stellar Mass | 1.1600 M☉ |
| Bolometric Luminosity | 2.934 L☉ |
| Metallicity [Fe/H] | 0.090 dex |
| Stellar Age | — |
| Apparent Magnitude | V: 12.081 · G: 11.946 |
| System Architecture | 1 Star, 2 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.085800 AU |
| Orbital Period | 8.527 days |
| Mean Orbital Velocity | 109.5 km/s |
| Orbital Eccentricity (e) | Circular (0.00) |
| Orbital Inclination (i) | 87.4288° |
| Mean Bulk Density | 2.85 g/cm³ (17.6 km/s vesc) |
| Insolation Flux | 390.3952 S⊕ (~531,328 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 1555.400 LY (476.882 pc) |