Kepler-538 b
Astrophysical Synthesis & Habitability Characterization
Kepler-538 b is a confirmed sub-neptune exoplanet orbiting the star Kepler-538, located approximately 508.7 light-years (155.96 parsecs) from the Solar System. First announced in 2016 by Kepler using the Transit detection technique (producing an estimated primary transit depth of 0.0543% across the stellar disk), this world measures 2.215 Earth radii and has a measured mass of 12.9 Earth masses. Combining its mass and radius yields a mean bulk density of 6.55 g/cm³ (an iron-enriched, high-compression rocky core), a surface gravity of 2.63 g⊕ (25.79 m/s²), and an escape velocity of 27 km/s.
In its orbital architecture around Kepler-538, Kepler-538 b completes one full revolution every 81.738 Earth days at a semi-major axis of 0.3554 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 47.3 km/s (compared to Earth's 29.8 km/s). Its moderate orbital eccentricity of e = 0.21 carries the world between 0.2808 AU at periapsis and 0.43 AU at apoapsis, driving measurable seasonal insolation cycles.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 417 K (+144°C / +291°F) and receiving 5.07 S⊕ (~6,900 W/m²), Kepler-538 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star Kepler-538 is classified as a stellar host with an effective photospheric temperature of 5,534 K, a radius of 0.8717 R☉, a mass of 0.892 M☉, an estimated bolometric luminosity of 0.639 L☉. Stellar evolution modeling indicates an estimated stellar age of 5.3 Gyr and a metallicity of [Fe/H] = -0.09 dex (near-solar heavy-element abundance). From Earth, Kepler-538 shines at apparent V-band magnitude 11.27 (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: Kepler · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | Kepler-538 |
| Spectral Type | Unclassified |
| Effective Temp (Teff) | 5,534 K |
| Stellar Radius | 0.8717 R☉ |
| Stellar Mass | 0.8920 M☉ |
| Bolometric Luminosity | 0.639 L☉ |
| Metallicity [Fe/H] | -0.090 dex |
| Stellar Age | 5.300 Gyr |
| Apparent Magnitude | V: 11.270 · G: 11.165 |
| System Architecture | 2 Stars, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.355400 AU |
| Orbital Period | 81.738 days |
| Mean Orbital Velocity | 47.3 km/s |
| Orbital Eccentricity (e) | 0.21000 |
| Orbital Inclination (i) | 89.7300° |
| Mean Bulk Density | 6.55 g/cm³ (27 km/s vesc) |
| Insolation Flux | 5.0700 S⊕ (~6,900 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 508.700 LY (155.956 pc) |