K2-201 c
Astrophysical Synthesis & Habitability Characterization
K2-201 c is a confirmed sub-neptune exoplanet orbiting the star K2-201, located approximately 645.6 light-years (197.93 parsecs) from the Solar System. First announced in 2018 by K2 using the Transit detection technique (producing an estimated primary transit depth of 0.1177% across the stellar disk), this world measures 3.286 Earth radii (0.29 Jupiter radii) and has a measured mass of 10.8 Earth masses. Combining its mass and radius yields a mean bulk density of 1.68 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 1 g⊕ (9.81 m/s²), and an escape velocity of 20.3 km/s.
In its orbital architecture around K2-201, K2-201 c completes one full revolution every 22.78 Earth days.
☁️ Atmospheric Regime (Volatile / Gas Envelope): With a radius of 3.286 R⊕, K2-201 c 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 K2-201 is classified as a stellar host with an effective photospheric temperature of 5,507 K, a radius of 0.8782 R☉, a mass of 0.9561 M☉, an estimated bolometric luminosity of 0.636 L☉. Stellar evolution modeling indicates a metallicity of [Fe/H] = 0.13 dex (metal-rich relative to the Sun). From Earth, K2-201 shines at apparent V-band magnitude 12.168 (faint and requiring research-grade or CCD telescopic photometry) in the Southern celestial hemisphere. The K2-201 system is a multi-planet architecture hosting 2 confirmed worlds, with K2-201 c sharing its stellar neighborhood alongside K2-201 b.
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 | K2-201 |
| Spectral Type | Unclassified |
| Effective Temp (Teff) | 5,507 K |
| Stellar Radius | 0.8782 R☉ |
| Stellar Mass | 0.9561 M☉ |
| Bolometric Luminosity | 0.636 L☉ |
| Metallicity [Fe/H] | 0.130 dex |
| Stellar Age | — |
| Apparent Magnitude | V: 12.168 · G: 11.943 |
| System Architecture | 1 Star, 2 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | — |
| Orbital Period | 22.78 days |
| Orbital Eccentricity (e) | Circular (0.00) |
| Orbital Inclination (i) | 89.2721° |
| Mean Bulk Density | 1.68 g/cm³ (20.3 km/s vesc) |
| Insolation Flux | — |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 645.600 LY (197.932 pc) |