K2-388 b
Astrophysical Synthesis & Habitability Characterization
K2-388 b is a confirmed sub-neptune exoplanet orbiting the star K2-388, located approximately 947.5 light-years (290.5 parsecs) from the Solar System. First announced in 2022 by K2 using the Transit detection technique (producing an estimated primary transit depth of 0.1544% across the stellar disk), this world measures 3.9 Earth radii (0.35 Jupiter radii) and has a measured mass of 14.5 Earth masses. Combining its mass and radius yields a mean bulk density of 1.35 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 0.95 g⊕ (9.32 m/s²), and an escape velocity of 21.6 km/s.
In its orbital architecture around K2-388, K2-388 b completes one full revolution every 6.339 Earth days.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 874 K (+601°C / +1114°F) and receiving 138.00 S⊕ (~187,818 W/m²), K2-388 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star K2-388 is classified as a solar-type yellow star of spectral type G8 with an effective photospheric temperature of 5,310 K, a radius of 0.91 R☉, a mass of 0.93 M☉, an estimated bolometric luminosity of 0.591 L☉. Stellar evolution modeling indicates a metallicity of [Fe/H] = 0.24 dex (metal-rich relative to the Sun). From Earth, K2-388 shines at apparent V-band magnitude 12.861 (faint and requiring research-grade or CCD telescopic photometry) in the Southern 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: K2 · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | K2-388 |
| Spectral Type | G8 |
| Effective Temp (Teff) | 5,310 K |
| Stellar Radius | 0.9100 R☉ |
| Stellar Mass | 0.9300 M☉ |
| Bolometric Luminosity | 0.591 L☉ |
| Metallicity [Fe/H] | 0.240 dex |
| Stellar Age | — |
| Apparent Magnitude | V: 12.861 · G: 12.636 |
| System Architecture | 1 Star, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | — |
| Orbital Period | 6.339 days |
| Orbital Eccentricity (e) | Circular (0.00) |
| Orbital Inclination (i) | — |
| Mean Bulk Density | 1.35 g/cm³ (21.6 km/s vesc) |
| Insolation Flux | 138.0000 S⊕ (~187,818 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 947.500 LY (290.495 pc) |