K2-390 b
Astrophysical Synthesis & Habitability Characterization
K2-390 b is a confirmed sub-neptune exoplanet orbiting the star K2-390, located approximately 1487.7 light-years (456.12 parsecs) from the Solar System. First announced in 2022 by K2 using the Transit detection technique (producing an estimated primary transit depth of 0.1958% across the stellar disk), this world measures 4.662 Earth radii (0.42 Jupiter radii) and has a measured mass of 19.6 Earth masses. Combining its mass and radius yields a mean bulk density of 1.07 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 0.9 g⊕ (8.83 m/s²), and an escape velocity of 22.9 km/s.
In its orbital architecture around K2-390, K2-390 b completes one full revolution every 3.313 Earth days.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 1119 K (+846°C / +1555°F) and receiving 260.97 S⊕ (~355,173 W/m²), K2-390 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star K2-390 is classified as a solar-type yellow star of spectral type G4 with an effective photospheric temperature of 5,558 K, a radius of 0.966 R☉, a mass of 0.789 M☉, an estimated bolometric luminosity of 0.799 L☉. Stellar evolution modeling indicates a metallicity of [Fe/H] = -0.116 dex (metal-poor relative to the Sun). From Earth, K2-390 shines at apparent V-band magnitude 13.611 (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 | K2-390 |
| Spectral Type | G4 |
| Effective Temp (Teff) | 5,558 K |
| Stellar Radius | 0.9660 R☉ |
| Stellar Mass | 0.7890 M☉ |
| Bolometric Luminosity | 0.799 L☉ |
| Metallicity [Fe/H] | -0.116 dex |
| Stellar Age | — |
| Apparent Magnitude | V: 13.611 · G: 13.343 |
| System Architecture | 1 Star, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | — |
| Orbital Period | 3.313 days |
| Orbital Eccentricity (e) | Circular (0.00) |
| Orbital Inclination (i) | — |
| Mean Bulk Density | 1.07 g/cm³ (22.9 km/s vesc) |
| Insolation Flux | 260.9650 S⊕ (~355,173 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 1487.700 LY (456.122 pc) |