K2-55 b
Astrophysical Synthesis & Habitability Characterization
K2-55 b is a confirmed sub-neptune exoplanet orbiting the star K2-55, located approximately 520.3 light-years (159.52 parsecs) from the Solar System. First announced in 2016 by K2 using the Transit detection technique (producing an estimated primary transit depth of 0.3227% across the stellar disk), this world measures 4.43 Earth radii (0.4 Jupiter radii) and has a measured mass of 44 Earth masses (0.14 Jupiter masses). Combining its mass and radius yields a mean bulk density of 2.79 g/cm³ (an intermediate density indicative of a deep water-ice mantle or dense volatile envelope), a surface gravity of 2.24 g⊕ (21.97 m/s²), and an escape velocity of 35.3 km/s.
In its orbital architecture around K2-55, K2-55 b completes one full revolution every 2.849 Earth days at a semi-major axis of 0.03486 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 133.1 km/s (compared to Earth's 29.8 km/s). Its moderate orbital eccentricity of e = 0.07 carries the world between 0.0324 AU at periapsis and 0.0373 AU at apoapsis, driving measurable seasonal insolation cycles.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 900 K (+627°C / +1161°F) and receiving 141.30 S⊕ (~192,309 W/m²), K2-55 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star K2-55 is classified as a stellar host with an effective photospheric temperature of 4,300 K, a radius of 0.715 R☉, a mass of 0.688 M☉, an estimated bolometric luminosity of 0.157 L☉. Stellar evolution modeling indicates a metallicity of [Fe/H] = 0.376 dex (metal-rich relative to the Sun). From Earth, K2-55 shines at apparent V-band magnitude 13.519 (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 | K2-55 |
| Spectral Type | Unclassified |
| Effective Temp (Teff) | 4,300 K |
| Stellar Radius | 0.7150 R☉ |
| Stellar Mass | 0.6880 M☉ |
| Bolometric Luminosity | 0.157 L☉ |
| Metallicity [Fe/H] | 0.376 dex |
| Stellar Age | — |
| Apparent Magnitude | V: 13.519 · G: 13.062 |
| System Architecture | 1 Star, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.034860 AU |
| Orbital Period | 2.849 days |
| Mean Orbital Velocity | 133.1 km/s |
| Orbital Eccentricity (e) | 0.07000 |
| Orbital Inclination (i) | 88.2000° |
| Mean Bulk Density | 2.79 g/cm³ (35.3 km/s vesc) |
| Insolation Flux | 141.3000 S⊕ (~192,309 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 520.300 LY (159.522 pc) |