K2-406 b
Astrophysical Synthesis & Habitability Characterization
K2-406 b is a confirmed sub-neptune exoplanet orbiting the star K2-406, located approximately 278.5 light-years (85.38 parsecs) from the Solar System. First announced in 2022 by K2 using the Transit detection technique (producing an estimated primary transit depth of 0.1927% across the stellar disk), this world measures 4.602 Earth radii (0.41 Jupiter radii) and has a measured mass of 19.2 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 K2-406, K2-406 b completes one full revolution every 22.549 Earth days.
☁️ Atmospheric Regime (Volatile / Gas Envelope): With a radius of 4.602 R⊕, K2-406 b exceeds the empirical ~1.8–2.2 R⊕ Fulton radius valley threshold, indicating a substantial hydrogen-helium or supercritical volatile envelope without a conventional solid terrestrial surface.
The host star K2-406 is classified as a solar-type yellow star of spectral type G4 with an effective photospheric temperature of 5,784 K, a radius of 0.961 R☉, a mass of 0.798 M☉, an estimated bolometric luminosity of 0.927 L☉. Stellar evolution modeling indicates a metallicity of [Fe/H] = -0.038 dex (near-solar heavy-element abundance). From Earth, K2-406 shines at apparent V-band magnitude 9.465 (accessible to binoculars and small amateur telescopes) 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 | K2-406 |
| Spectral Type | G4 |
| Effective Temp (Teff) | 5,784 K |
| Stellar Radius | 0.9610 R☉ |
| Stellar Mass | 0.7980 M☉ |
| Bolometric Luminosity | 0.927 L☉ |
| Metallicity [Fe/H] | -0.038 dex |
| Stellar Age | — |
| Apparent Magnitude | V: 9.465 · G: 9.494 |
| System Architecture | 1 Star, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | — |
| Orbital Period | 22.549 days |
| Orbital Eccentricity (e) | Circular (0.00) |
| Orbital Inclination (i) | — |
| Mean Bulk Density | 1.09 g/cm³ (22.8 km/s vesc) |
| Insolation Flux | — |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 278.500 LY (85.375 pc) |