K2-266 d
Astrophysical Synthesis & Habitability Characterization
K2-266 d is a confirmed sub-neptune exoplanet orbiting the star K2-266, located approximately 253 light-years (77.56 parsecs) from the Solar System. First announced in 2018 by K2 using the Transit detection technique (producing an estimated primary transit depth of 0.146% across the stellar disk), this world measures 2.93 Earth radii and has a measured mass of 8.9 Earth masses. Combining its mass and radius yields a mean bulk density of 1.95 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 1.04 g⊕ (10.2 m/s²), and an escape velocity of 19.5 km/s.
In its orbital architecture around K2-266, K2-266 d completes one full revolution every 14.697 Earth days at a semi-major axis of 0.1035 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 76.6 km/s (compared to Earth's 29.8 km/s). With a near-circular eccentricity of e = 0.047 (ranging from 0.0986 AU at periapsis to 0.1084 AU at apoapsis), the planet experiences minimal orbital distance variation.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 538 K (+265°C / +509°F) and receiving 13.95 S⊕ (~18,986 W/m²), K2-266 d orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star K2-266 is classified as a stellar host with an effective photospheric temperature of 4,285 K, a radius of 0.703 R☉, a mass of 0.686 M☉, an estimated bolometric luminosity of 0.149 L☉. Stellar evolution modeling indicates a metallicity of [Fe/H] = -0.12 dex (metal-poor relative to the Sun). From Earth, K2-266 shines at apparent V-band magnitude 11.625 (faint and requiring research-grade or CCD telescopic photometry) in the Northern celestial hemisphere. The K2-266 system is a multi-planet architecture hosting 4 confirmed worlds, with K2-266 d sharing its stellar neighborhood alongside K2-266 b, K2-266 c, K2-266 e.
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 | K2-266 |
| Spectral Type | Unclassified |
| Effective Temp (Teff) | 4,285 K |
| Stellar Radius | 0.7030 R☉ |
| Stellar Mass | 0.6860 M☉ |
| Bolometric Luminosity | 0.149 L☉ |
| Metallicity [Fe/H] | -0.120 dex |
| Stellar Age | — |
| Apparent Magnitude | V: 11.625 · G: 11.353 |
| System Architecture | 2 Stars, 4 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.103500 AU |
| Orbital Period | 14.697 days |
| Mean Orbital Velocity | 76.6 km/s |
| Orbital Eccentricity (e) | 0.04700 |
| Orbital Inclination (i) | 89.4600° |
| Mean Bulk Density | 1.95 g/cm³ (19.5 km/s vesc) |
| Insolation Flux | 13.9500 S⊕ (~18,986 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 253.000 LY (77.559 pc) |