K2-158 b
Astrophysical Synthesis & Habitability Characterization
K2-158 b is a confirmed sub-neptune exoplanet orbiting the star K2-158, located approximately 643.5 light-years (197.3 parsecs) from the Solar System. First announced in 2018 by K2 using the Transit detection technique (producing an estimated primary transit depth of 0.0649% across the stellar disk), this world measures 2.64 Earth radii and has a measured mass of 7.46 Earth masses. Combining its mass and radius yields a mean bulk density of 2.24 g/cm³ (an intermediate density indicative of a deep water-ice mantle or dense volatile envelope), a surface gravity of 1.07 g⊕ (10.49 m/s²), and an escape velocity of 18.8 km/s.
In its orbital architecture around K2-158, K2-158 b completes one full revolution every 10.06 Earth days at a semi-major axis of 0.0887 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 95.9 km/s (compared to Earth's 29.8 km/s).
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 794 K (+521°C / +970°F) and receiving 87.33 S⊕ (~118,860 W/m²), K2-158 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star K2-158 is classified as a stellar host with an effective photospheric temperature of 5,503 K, a radius of 0.95 R☉, a mass of 0.92 M☉, an estimated bolometric luminosity of 0.743 L☉. Stellar evolution modeling indicates a metallicity of [Fe/H] = 0.07 dex (metal-rich relative to the Sun). From Earth, K2-158 shines at apparent V-band magnitude 11.774 (faint and requiring research-grade or CCD telescopic photometry) in the Southern celestial hemisphere. The K2-158 system is a multi-planet architecture hosting 2 confirmed worlds, with K2-158 b sharing its stellar neighborhood alongside K2-158 c.
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 | K2-158 |
| Spectral Type | Unclassified |
| Effective Temp (Teff) | 5,503 K |
| Stellar Radius | 0.9500 R☉ |
| Stellar Mass | 0.9200 M☉ |
| Bolometric Luminosity | 0.743 L☉ |
| Metallicity [Fe/H] | 0.070 dex |
| Stellar Age | — |
| Apparent Magnitude | V: 11.774 · G: 11.613 |
| System Architecture | 1 Star, 2 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.088700 AU |
| Orbital Period | 10.06 days |
| Mean Orbital Velocity | 95.9 km/s |
| Orbital Eccentricity (e) | Circular (0.00) |
| Orbital Inclination (i) | 88.4045° |
| Mean Bulk Density | 2.24 g/cm³ (18.8 km/s vesc) |
| Insolation Flux | 87.3327 S⊕ (~118,860 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 643.500 LY (197.299 pc) |