Kepler-78 b
Astrophysical Synthesis & Habitability Characterization
Kepler-78 b is a confirmed terrestrial exoplanet orbiting the star Kepler-78, located approximately 405.7 light-years (124.38 parsecs) from the Solar System. First announced in 2013 by Kepler using the Transit detection technique (producing an estimated primary transit depth of 0.0217% across the stellar disk), this world measures 1.201 Earth radii and has a measured mass of 1.68 Earth masses. Combining its mass and radius yields a mean bulk density of 5.35 g/cm³ (a terrestrial silicate-iron composition comparable to Earth (5.51 g/cm³)), a surface gravity of 1.16 g⊕ (11.38 m/s²), and an escape velocity of 13.2 km/s.
In its orbital architecture around Kepler-78, Kepler-78 b completes one full revolution every 0.355 Earth days at a semi-major axis of 0.00901 AU (an ultra-close orbit less than one-seventh of Mercury's 0.387 AU distance from the Sun, where strong stellar tidal forces typically induce synchronous rotation). Its mean orbital velocity is approximately 276.1 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 2223 K (+1950°C / +3542°F) and receiving 4,070.00 S⊕ (~5,539,270 W/m²), Kepler-78 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star Kepler-78 is classified as a solar-type yellow star of spectral type G with an effective photospheric temperature of 5,058 K, a radius of 0.7475 R☉, a mass of 0.779 M☉, an estimated bolometric luminosity of 0.328 L☉. Stellar evolution modeling indicates an estimated stellar age of 0.625 Gyr and a metallicity of [Fe/H] = -0.18 dex (metal-poor relative to the Sun). From Earth, Kepler-78 shines at apparent V-band magnitude 11.717 (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-78 |
| Spectral Type | G |
| Effective Temp (Teff) | 5,058 K |
| Stellar Radius | 0.7475 R☉ |
| Stellar Mass | 0.7790 M☉ |
| Bolometric Luminosity | 0.328 L☉ |
| Metallicity [Fe/H] | -0.180 dex |
| Stellar Age | 0.625 Gyr |
| Apparent Magnitude | V: 11.717 · G: 11.529 |
| System Architecture | 2 Stars, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.009010 AU |
| Orbital Period | 0.355 days |
| Mean Orbital Velocity | 276.1 km/s |
| Orbital Eccentricity (e) | 0.00000 |
| Orbital Inclination (i) | 75.2000° |
| Mean Bulk Density | 5.35 g/cm³ (13.2 km/s vesc) |
| Insolation Flux | 4070.0000 S⊕ (~5,539,270 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 405.700 LY (124.376 pc) |