K2-356 b
Astrophysical Synthesis & Habitability Characterization
K2-356 b is a confirmed sub-neptune exoplanet orbiting the star K2-356, located approximately 1159.6 light-years (355.54 parsecs) from the Solar System. First announced in 2021 by K2 using the Transit detection technique (producing an estimated primary transit depth of 0.0596% across the stellar disk), this world measures 2.29 Earth radii and has a measured mass of 5.86 Earth masses. Combining its mass and radius yields a mean bulk density of 2.69 g/cm³ (an intermediate density indicative of a deep water-ice mantle or dense volatile envelope), a surface gravity of 1.12 g⊕ (10.98 m/s²), and an escape velocity of 17.9 km/s.
In its orbital architecture around K2-356, K2-356 b completes one full revolution every 21.027 Earth days at a semi-major axis of 0.1599 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 82.7 km/s (compared to Earth's 29.8 km/s).
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 624 K (+351°C / +664°F) and receiving 22.31 S⊕ (~30,368 W/m²), K2-356 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star K2-356 is classified as a stellar host with an effective photospheric temperature of 5,568 K, a radius of 0.86 R☉, a mass of 0.9 M☉, an estimated bolometric luminosity of 0.638 L☉. Stellar evolution modeling indicates a metallicity of [Fe/H] = -0.11 dex (metal-poor relative to the Sun). From Earth, K2-356 shines at apparent V-band magnitude 13.268 (faint and requiring research-grade or CCD telescopic photometry) in the Northern 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 | K2-356 |
| Spectral Type | Unclassified |
| Effective Temp (Teff) | 5,568 K |
| Stellar Radius | 0.8600 R☉ |
| Stellar Mass | 0.9000 M☉ |
| Bolometric Luminosity | 0.638 L☉ |
| Metallicity [Fe/H] | -0.110 dex |
| Stellar Age | — |
| Apparent Magnitude | V: 13.268 · G: 13.148 |
| System Architecture | 1 Star, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.159900 AU |
| Orbital Period | 21.027 days |
| Mean Orbital Velocity | 82.7 km/s |
| Orbital Eccentricity (e) | Circular (0.00) |
| Orbital Inclination (i) | — |
| Mean Bulk Density | 2.69 g/cm³ (17.9 km/s vesc) |
| Insolation Flux | 22.3128 S⊕ (~30,368 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 1159.600 LY (355.540 pc) |