K2-405 b
Astrophysical Synthesis & Habitability Characterization
K2-405 b is a confirmed sub-neptune exoplanet orbiting the star K2-405, located approximately 643.3 light-years (197.23 parsecs) from the Solar System. First announced in 2022 by K2 using the Transit detection technique (producing an estimated primary transit depth of 0.2998% across the stellar disk), this world measures 4.569 Earth radii (0.41 Jupiter radii) and has a measured mass of 18.9 Earth masses. Combining its mass and radius yields a mean bulk density of 1.09 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 0.91 g⊕ (8.92 m/s²), and an escape velocity of 22.8 km/s.
In its orbital architecture around K2-405, K2-405 b completes one full revolution every 3.435 Earth days.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 969 K (+696°C / +1285°F) and receiving 146.58 S⊕ (~199,491 W/m²), K2-405 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star K2-405 is classified as an orange K-type star of spectral type K0 with an effective photospheric temperature of 4,927 K, a radius of 0.765 R☉, a mass of 1.034 M☉, an estimated bolometric luminosity of 0.309 L☉. Stellar evolution modeling indicates a metallicity of [Fe/H] = 0.132 dex (metal-rich relative to the Sun). From Earth, K2-405 shines at apparent V-band magnitude 12.816 (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 | K2-405 |
| Spectral Type | K0 |
| Effective Temp (Teff) | 4,927 K |
| Stellar Radius | 0.7650 R☉ |
| Stellar Mass | 1.0340 M☉ |
| Bolometric Luminosity | 0.309 L☉ |
| Metallicity [Fe/H] | 0.132 dex |
| Stellar Age | — |
| Apparent Magnitude | V: 12.816 · G: 12.591 |
| System Architecture | 1 Star, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | — |
| Orbital Period | 3.435 days |
| Orbital Eccentricity (e) | Circular (0.00) |
| Orbital Inclination (i) | 87.6647° |
| Mean Bulk Density | 1.09 g/cm³ (22.8 km/s vesc) |
| Insolation Flux | 146.5770 S⊕ (~199,491 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 643.300 LY (197.234 pc) |