K2-255 b
Astrophysical Synthesis & Habitability Characterization
K2-255 b is a confirmed sub-neptune exoplanet orbiting the star K2-255, located approximately 624.9 light-years (191.61 parsecs) from the Solar System. First announced in 2018 by K2 using the Transit detection technique (producing an estimated primary transit depth of 0.1485% across the stellar disk), this world measures 2.9 Earth radii and has a measured mass of 8.75 Earth masses. Combining its mass and radius yields a mean bulk density of 1.98 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 19.4 km/s.
In its orbital architecture around K2-255, K2-255 b completes one full revolution every 1.964 Earth days at a semi-major axis of 0.0274 AU (an ultra-close orbit less than one-seventh of Mercury's 0.387 AU distance from the Sun, where strong stellar tidal forces typically induce synchronous rotation). Its mean orbital velocity is approximately 151.8 km/s (compared to Earth's 29.8 km/s).
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 1034 K (+761°C / +1402°F) and receiving 215.91 S⊕ (~293,854 W/m²), K2-255 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star K2-255 is classified as a stellar host with an effective photospheric temperature of 4,676 K, a radius of 0.69 R☉, a mass of 0.71 M☉, an estimated bolometric luminosity of 0.204 L☉. Stellar evolution modeling indicates a metallicity of [Fe/H] = -0.14 dex (metal-poor relative to the Sun). From Earth, K2-255 shines at apparent V-band magnitude 13.662 (faint and requiring research-grade or CCD telescopic photometry) in the Southern celestial hemisphere.
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 | K2-255 |
| Spectral Type | Unclassified |
| Effective Temp (Teff) | 4,676 K |
| Stellar Radius | 0.6900 R☉ |
| Stellar Mass | 0.7100 M☉ |
| Bolometric Luminosity | 0.204 L☉ |
| Metallicity [Fe/H] | -0.140 dex |
| Stellar Age | — |
| Apparent Magnitude | V: 13.662 · G: 13.309 |
| System Architecture | 1 Star, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.027400 AU |
| Orbital Period | 1.964 days |
| Mean Orbital Velocity | 151.8 km/s |
| Orbital Eccentricity (e) | Circular (0.00) |
| Orbital Inclination (i) | — |
| Mean Bulk Density | 1.98 g/cm³ (19.4 km/s vesc) |
| Insolation Flux | 215.9107 S⊕ (~293,854 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 624.900 LY (191.608 pc) |