K2-403 b
Astrophysical Synthesis & Habitability Characterization
K2-403 b is a confirmed sub-neptune exoplanet orbiting the star K2-403, located approximately 804.3 light-years (246.6 parsecs) from the Solar System. First announced in 2022 by K2 using the Transit detection technique (producing an estimated primary transit depth of 0.3045% across the stellar disk), this world measures 5.333 Earth radii (0.48 Jupiter radii) and has a measured mass of 24.6 Earth masses. Combining its mass and radius yields a mean bulk density of 0.89 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 0.86 g⊕ (8.43 m/s²), and an escape velocity of 24 km/s.
In its orbital architecture around K2-403, K2-403 b completes one full revolution every 33.59 Earth days.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 949 K (+676°C / +1249°F) and receiving 134.88 S⊕ (~183,576 W/m²), K2-403 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star K2-403 is classified as a solar-type yellow star of spectral type G4 with an effective photospheric temperature of 5,511 K, a radius of 0.886 R☉, a mass of 0.784 M☉, an estimated bolometric luminosity of 0.65 L☉. Stellar evolution modeling indicates a metallicity of [Fe/H] = -0.162 dex (metal-poor relative to the Sun). From Earth, K2-403 shines at apparent V-band magnitude 12.305 (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: K2 · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | K2-403 |
| Spectral Type | G4 |
| Effective Temp (Teff) | 5,511 K |
| Stellar Radius | 0.8860 R☉ |
| Stellar Mass | 0.7840 M☉ |
| Bolometric Luminosity | 0.65 L☉ |
| Metallicity [Fe/H] | -0.162 dex |
| Stellar Age | — |
| Apparent Magnitude | V: 12.305 · G: 12.152 |
| System Architecture | 1 Star, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | — |
| Orbital Period | 33.59 days |
| Orbital Eccentricity (e) | Circular (0.00) |
| Orbital Inclination (i) | — |
| Mean Bulk Density | 0.89 g/cm³ (24 km/s vesc) |
| Insolation Flux | 134.8830 S⊕ (~183,576 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 804.300 LY (246.599 pc) |