Kepler-254 d
Astrophysical Synthesis & Habitability Characterization
Kepler-254 d is a confirmed sub-neptune exoplanet orbiting the star Kepler-254, located approximately 4531.9 light-years (1389.48 parsecs) from the Solar System. First announced in 2014 by Kepler using the Transit detection technique (producing an estimated primary transit depth of 0.0634% across the stellar disk), this world measures 2.5 Earth radii and has a measured mass of 6.8 Earth masses. Combining its mass and radius yields a mean bulk density of 2.4 g/cm³ (an intermediate density indicative of a deep water-ice mantle or dense volatile envelope), a surface gravity of 1.09 g⊕ (10.69 m/s²), and an escape velocity of 18.4 km/s.
In its orbital architecture around Kepler-254, Kepler-254 d completes one full revolution every 18.746 Earth days at a semi-major axis of 0.139 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 80.7 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 686 K (+413°C / +775°F) and receiving 38.84 S⊕ (~52,867 W/m²), Kepler-254 d orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star Kepler-254 is classified as a stellar host with an effective photospheric temperature of 5,957 K, a radius of 0.91 R☉, a mass of 0.849 M☉, an estimated bolometric luminosity of 0.936 L☉. Stellar evolution modeling indicates an estimated stellar age of 0.3 Gyr and a metallicity of [Fe/H] = -0.13 dex (metal-poor relative to the Sun). From Earth, Kepler-254 shines at apparent V-band magnitude 16.012 (faint and requiring research-grade or CCD telescopic photometry) in the Northern celestial hemisphere. The Kepler-254 system is a multi-planet architecture hosting 3 confirmed worlds, with Kepler-254 d sharing its stellar neighborhood alongside Kepler-254 b, Kepler-254 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-254 |
| Spectral Type | Unclassified |
| Effective Temp (Teff) | 5,957 K |
| Stellar Radius | 0.9100 R☉ |
| Stellar Mass | 0.8490 M☉ |
| Bolometric Luminosity | 0.936 L☉ |
| Metallicity [Fe/H] | -0.130 dex |
| Stellar Age | 0.300 Gyr |
| Apparent Magnitude | V: 16.012 · G: 15.838 |
| System Architecture | 1 Star, 3 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.139000 AU |
| Orbital Period | 18.746 days |
| Mean Orbital Velocity | 80.7 km/s |
| Orbital Eccentricity (e) | 0.00000 |
| Orbital Inclination (i) | 89.1100° |
| Mean Bulk Density | 2.4 g/cm³ (18.4 km/s vesc) |
| Insolation Flux | 38.8440 S⊕ (~52,867 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 4531.900 LY (1389.480 pc) |