Kepler-388 b
Astrophysical Synthesis & Habitability Characterization
Kepler-388 b is a confirmed terrestrial exoplanet orbiting the star Kepler-388, located approximately 1386.2 light-years (425 parsecs) from the Solar System. First announced in 2014 by Kepler using the Transit detection technique (producing an estimated primary transit depth of 0.0161% across the stellar disk), this world measures 0.81 Earth radii and has a measured mass of 0.457 Earth masses. Combining its mass and radius yields a mean bulk density of 4.74 g/cm³ (a terrestrial silicate-iron composition comparable to Earth (5.51 g/cm³)), a surface gravity of 0.7 g⊕ (6.86 m/s²), and an escape velocity of 8.4 km/s.
In its orbital architecture around Kepler-388, Kepler-388 b completes one full revolution every 3.173 Earth days at a semi-major axis of 0.036 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 123.4 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 830 K (+557°C / +1035°F) and receiving 112.21 S⊕ (~152,718 W/m²), Kepler-388 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star Kepler-388 is classified as a stellar host with an effective photospheric temperature of 4,498 K, a radius of 0.586 R☉, a mass of 0.635 M☉, an estimated bolometric luminosity of 0.126 L☉. Stellar evolution modeling indicates an estimated stellar age of 13.9 Gyr and a metallicity of [Fe/H] = 0 dex (near-solar heavy-element abundance). From Earth, Kepler-388 shines at apparent V-band magnitude 15.218 (faint and requiring research-grade or CCD telescopic photometry) in the Northern celestial hemisphere. The Kepler-388 system is a multi-planet architecture hosting 2 confirmed worlds, with Kepler-388 b sharing its stellar neighborhood alongside Kepler-388 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-388 |
| Spectral Type | Unclassified |
| Effective Temp (Teff) | 4,498 K |
| Stellar Radius | 0.5860 R☉ |
| Stellar Mass | 0.6350 M☉ |
| Bolometric Luminosity | 0.126 L☉ |
| Metallicity [Fe/H] | 0.000 dex |
| Stellar Age | 13.900 Gyr |
| Apparent Magnitude | V: 15.218 · G: 15.002 |
| System Architecture | 1 Star, 2 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.036000 AU |
| Orbital Period | 3.173 days |
| Mean Orbital Velocity | 123.4 km/s |
| Orbital Eccentricity (e) | 0.00000 |
| Orbital Inclination (i) | 89.6200° |
| Mean Bulk Density | 4.74 g/cm³ (8.4 km/s vesc) |
| Insolation Flux | 112.2100 S⊕ (~152,718 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 1386.200 LY (425.000 pc) |