Kepler-478 b
Astrophysical Synthesis & Habitability Characterization
Kepler-478 b is a confirmed sub-neptune exoplanet orbiting the star Kepler-478, located approximately 1369.9 light-years (420 parsecs) from the Solar System. First announced in 2016 by Kepler using the Transit detection technique (producing an estimated primary transit depth of 0.0964% across the stellar disk), this world measures 2.71 Earth radii and has a measured mass of 7.8 Earth masses. Combining its mass and radius yields a mean bulk density of 2.16 g/cm³ (an intermediate density indicative of a deep water-ice mantle or dense volatile envelope), a surface gravity of 1.06 g⊕ (10.4 m/s²), and an escape velocity of 19 km/s.
In its orbital architecture around Kepler-478, Kepler-478 b completes one full revolution every 13.222 Earth days at a semi-major axis of 0.1032 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 640 K (+367°C / +693°F) and receiving 39.56 S⊕ (~53,841 W/m²), Kepler-478 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star Kepler-478 is classified as a stellar host with an effective photospheric temperature of 5,210 K, a radius of 0.8 R☉, a mass of 0.85 M☉, an estimated bolometric luminosity of 0.423 L☉. Stellar evolution modeling indicates an estimated stellar age of 4.9 Gyr and a metallicity of [Fe/H] = -0.03 dex (near-solar heavy-element abundance). From Earth, Kepler-478 shines at apparent V-band magnitude 14.156 (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-478 |
| Spectral Type | Unclassified |
| Effective Temp (Teff) | 5,210 K |
| Stellar Radius | 0.8000 R☉ |
| Stellar Mass | 0.8500 M☉ |
| Bolometric Luminosity | 0.423 L☉ |
| Metallicity [Fe/H] | -0.030 dex |
| Stellar Age | 4.900 Gyr |
| Apparent Magnitude | V: 14.156 · G: 13.967 |
| System Architecture | 1 Star, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.103200 AU |
| Orbital Period | 13.222 days |
| Mean Orbital Velocity | 84.9 km/s |
| Orbital Eccentricity (e) | 0.00000 |
| Orbital Inclination (i) | 89.2300° |
| Mean Bulk Density | 2.16 g/cm³ (19 km/s vesc) |
| Insolation Flux | 39.5600 S⊕ (~53,841 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 1369.900 LY (420.000 pc) |