Kepler-1388 d
Astrophysical Synthesis & Habitability Characterization
Kepler-1388 d is a confirmed sub-neptune exoplanet orbiting the star Kepler-1388, located approximately 1480.1 light-years (453.8 parsecs) from the Solar System. First announced in 2016 by Kepler using the Transit detection technique (producing an estimated primary transit depth of 0.1848% across the stellar disk), this world measures 2.86 Earth radii and has a measured mass of 8.55 Earth masses. Combining its mass and radius yields a mean bulk density of 2.02 g/cm³ (an intermediate density indicative of a deep water-ice mantle or dense volatile envelope), a surface gravity of 1.05 g⊕ (10.3 m/s²), and an escape velocity of 19.3 km/s.
In its orbital architecture around Kepler-1388, Kepler-1388 d completes one full revolution every 20.957 Earth days at a semi-major axis of 0.126 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 65.4 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 363 K (+90°C / +194°F) and receiving 8.66 S⊕ (~11,786 W/m²), Kepler-1388 d orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star Kepler-1388 is classified as a stellar host with an effective photospheric temperature of 4,098 K, a radius of 0.61 R☉, a mass of 0.63 M☉, an estimated bolometric luminosity of 0.094 L☉. Stellar evolution modeling indicates an estimated stellar age of 4.47 Gyr and a metallicity of [Fe/H] = 0.02 dex (near-solar heavy-element abundance). From Earth, Kepler-1388 shines at apparent V-band magnitude 16.43 (faint and requiring research-grade or CCD telescopic photometry) in the Northern celestial hemisphere. The Kepler-1388 system is a multi-planet architecture hosting 4 confirmed worlds, with Kepler-1388 d sharing its stellar neighborhood alongside Kepler-1388 c, Kepler-1388 b, Kepler-1388 e.
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-1388 |
| Spectral Type | Unclassified |
| Effective Temp (Teff) | 4,098 K |
| Stellar Radius | 0.6100 R☉ |
| Stellar Mass | 0.6300 M☉ |
| Bolometric Luminosity | 0.094 L☉ |
| Metallicity [Fe/H] | 0.020 dex |
| Stellar Age | 4.470 Gyr |
| Apparent Magnitude | V: 16.430 · G: 16.294 |
| System Architecture | 1 Star, 4 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.126000 AU |
| Orbital Period | 20.957 days |
| Mean Orbital Velocity | 65.4 km/s |
| Orbital Eccentricity (e) | 0.00000 |
| Orbital Inclination (i) | 89.8600° |
| Mean Bulk Density | 2.02 g/cm³ (19.3 km/s vesc) |
| Insolation Flux | 8.6600 S⊕ (~11,786 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 1480.100 LY (453.795 pc) |