K2-254 c
Astrophysical Synthesis & Habitability Characterization
K2-254 c is a confirmed sub-neptune exoplanet orbiting the star K2-254, located approximately 742.9 light-years (227.78 parsecs) from the Solar System. First announced in 2018 by K2 using the Transit detection technique (producing an estimated primary transit depth of 0.0898% 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 K2-254, K2-254 c completes one full revolution every 12.118 Earth days at a semi-major axis of 0.0923 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 82.9 km/s (compared to Earth's 29.8 km/s).
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 551 K (+278°C / +532°F) and receiving 17.67 S⊕ (~24,045 W/m²), K2-254 c orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star K2-254 is classified as a stellar host with an effective photospheric temperature of 4,629 K, a radius of 0.67 R☉, a mass of 0.71 M☉, an estimated bolometric luminosity of 0.185 L☉. Stellar evolution modeling indicates a metallicity of [Fe/H] = -0.14 dex (metal-poor relative to the Sun). From Earth, K2-254 shines at apparent V-band magnitude 14.238 (faint and requiring research-grade or CCD telescopic photometry) in the Southern celestial hemisphere. The K2-254 system is a multi-planet architecture hosting 2 confirmed worlds, with K2-254 c sharing its stellar neighborhood alongside K2-254 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: K2 · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | K2-254 |
| Spectral Type | Unclassified |
| Effective Temp (Teff) | 4,629 K |
| Stellar Radius | 0.6700 R☉ |
| Stellar Mass | 0.7100 M☉ |
| Bolometric Luminosity | 0.185 L☉ |
| Metallicity [Fe/H] | -0.140 dex |
| Stellar Age | — |
| Apparent Magnitude | V: 14.238 · G: 13.743 |
| System Architecture | 1 Star, 2 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.092300 AU |
| Orbital Period | 12.118 days |
| Mean Orbital Velocity | 82.9 km/s |
| Orbital Eccentricity (e) | Circular (0.00) |
| Orbital Inclination (i) | — |
| Mean Bulk Density | 2.85 g/cm³ (17.6 km/s vesc) |
| Insolation Flux | 17.6668 S⊕ (~24,045 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 742.900 LY (227.775 pc) |