Kepler-258 b
Astrophysical Synthesis & Habitability Characterization
Kepler-258 b is a confirmed sub-neptune exoplanet orbiting the star Kepler-258, located approximately 1878.6 light-years (575.99 parsecs) from the Solar System. First announced in 2014 by Kepler using the Transit detection technique (producing an estimated primary transit depth of 0.1655% across the stellar disk), this world measures 4.06 Earth radii (0.36 Jupiter radii) and has a measured mass of 15.5 Earth masses. Combining its mass and radius yields a mean bulk density of 1.28 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 0.94 g⊕ (9.22 m/s²), and an escape velocity of 21.9 km/s.
In its orbital architecture around Kepler-258, Kepler-258 b completes one full revolution every 13.197 Earth days at a semi-major axis of 0.103 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 84.9 km/s (compared to Earth's 29.8 km/s). The orbit is modeled as circular (e = 0.00), maintaining a constant stellar distance throughout its year.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 642 K (+369°C / +696°F) and receiving 27.79 S⊕ (~37,824 W/m²), Kepler-258 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star Kepler-258 is classified as a stellar host with an effective photospheric temperature of 4,942 K, a radius of 0.915 R☉, a mass of 0.82 M☉, an estimated bolometric luminosity of 0.448 L☉. Stellar evolution modeling indicates an estimated stellar age of 13.7 Gyr and a metallicity of [Fe/H] = 0.303 dex (metal-rich relative to the Sun). From Earth, Kepler-258 shines at apparent V-band magnitude 15.49 (faint and requiring research-grade or CCD telescopic photometry) in the Northern celestial hemisphere. The Kepler-258 system is a multi-planet architecture hosting 2 confirmed worlds, with Kepler-258 b sharing its stellar neighborhood alongside Kepler-258 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: Kepler · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | Kepler-258 |
| Spectral Type | Unclassified |
| Effective Temp (Teff) | 4,942 K |
| Stellar Radius | 0.9150 R☉ |
| Stellar Mass | 0.8200 M☉ |
| Bolometric Luminosity | 0.448 L☉ |
| Metallicity [Fe/H] | 0.303 dex |
| Stellar Age | 13.700 Gyr |
| Apparent Magnitude | V: 15.490 · G: 15.201 |
| System Architecture | 1 Star, 2 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.103000 AU |
| Orbital Period | 13.197 days |
| Mean Orbital Velocity | 84.9 km/s |
| Orbital Eccentricity (e) | 0.00000 |
| Orbital Inclination (i) | 88.7100° |
| Mean Bulk Density | 1.28 g/cm³ (21.9 km/s vesc) |
| Insolation Flux | 27.7910 S⊕ (~37,824 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 1878.600 LY (575.988 pc) |