K2-401 b
Astrophysical Synthesis & Habitability Characterization
K2-401 b is a confirmed sub-neptune exoplanet orbiting the star K2-401, located approximately 654.7 light-years (200.73 parsecs) from the Solar System. First announced in 2022 by K2 using the Transit detection technique (producing an estimated primary transit depth of 0.0944% across the stellar disk), this world measures 2.262 Earth radii and has a measured mass of 5.74 Earth masses. Combining its mass and radius yields a mean bulk density of 2.73 g/cm³ (an intermediate density indicative of a deep water-ice mantle or dense volatile envelope), a surface gravity of 1.12 g⊕ (10.98 m/s²), and an escape velocity of 17.8 km/s.
In its orbital architecture around K2-401, K2-401 b completes one full revolution every 6.293 Earth days.
☁️ Atmospheric Regime (Volatile / Gas Envelope): With a radius of 2.262 R⊕, K2-401 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 K2-401 is classified as an orange K-type star of spectral type K7 with an effective photospheric temperature of 4,213 K, a radius of 0.675 R☉, a mass of 0.87 M☉, an estimated bolometric luminosity of 0.129 L☉. Stellar evolution modeling indicates a metallicity of [Fe/H] = -0.098 dex (near-solar heavy-element abundance). From Earth, K2-401 shines at apparent V-band magnitude 14.014 (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 | K2-401 |
| Spectral Type | K7 |
| Effective Temp (Teff) | 4,213 K |
| Stellar Radius | 0.6750 R☉ |
| Stellar Mass | 0.8700 M☉ |
| Bolometric Luminosity | 0.129 L☉ |
| Metallicity [Fe/H] | -0.098 dex |
| Stellar Age | — |
| Apparent Magnitude | V: 14.014 · G: 13.694 |
| System Architecture | 1 Star, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | — |
| Orbital Period | 6.293 days |
| Orbital Eccentricity (e) | Circular (0.00) |
| Orbital Inclination (i) | — |
| Mean Bulk Density | 2.73 g/cm³ (17.8 km/s vesc) |
| Insolation Flux | — |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 654.700 LY (200.727 pc) |