K2-199 c
Astrophysical Synthesis & Habitability Characterization
K2-199 c is a confirmed sub-neptune exoplanet orbiting the star K2-199, located approximately 350.7 light-years (107.52 parsecs) from the Solar System. First announced in 2018 by K2 using the Transit detection technique (producing an estimated primary transit depth of 0.1468% across the stellar disk), this world measures 2.85 Earth radii and has a measured mass of 12.4 Earth masses. Combining its mass and radius yields a mean bulk density of 2.95 g/cm³ (an intermediate density indicative of a deep water-ice mantle or dense volatile envelope), a surface gravity of 1.53 g⊕ (15 m/s²), and an escape velocity of 23.3 km/s.
In its orbital architecture around K2-199, K2-199 c completes one full revolution every 7.374 Earth days at a semi-major axis of 0.0662 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 97.7 km/s (compared to Earth's 29.8 km/s). With a near-circular eccentricity of e = 0.03 (ranging from 0.0642 AU at periapsis to 0.0682 AU at apoapsis), the planet experiences minimal orbital distance variation.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 694 K (+421°C / +790°F) and receiving 38.60 S⊕ (~52,535 W/m²), K2-199 c orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star K2-199 is classified as a stellar host with an effective photospheric temperature of 4,491 K, a radius of 0.682 R☉, a mass of 0.711 M☉, an estimated bolometric luminosity of 0.17 L☉. Stellar evolution modeling indicates an estimated stellar age of 5.04 Gyr and a metallicity of [Fe/H] = -0.01 dex (near-solar heavy-element abundance). From Earth, K2-199 shines at apparent V-band magnitude 12.358 (faint and requiring research-grade or CCD telescopic photometry) in the Southern celestial hemisphere. The K2-199 system is a multi-planet architecture hosting 2 confirmed worlds, with K2-199 c sharing its stellar neighborhood alongside K2-199 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 | K2-199 |
| Spectral Type | Unclassified |
| Effective Temp (Teff) | 4,491 K |
| Stellar Radius | 0.6820 R☉ |
| Stellar Mass | 0.7110 M☉ |
| Bolometric Luminosity | 0.17 L☉ |
| Metallicity [Fe/H] | -0.010 dex |
| Stellar Age | 5.040 Gyr |
| Apparent Magnitude | V: 12.358 · G: 11.905 |
| System Architecture | 1 Star, 2 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.066200 AU |
| Orbital Period | 7.374 days |
| Mean Orbital Velocity | 97.7 km/s |
| Orbital Eccentricity (e) | 0.03000 |
| Orbital Inclination (i) | 87.7000° |
| Mean Bulk Density | 2.95 g/cm³ (23.3 km/s vesc) |
| Insolation Flux | 38.6000 S⊕ (~52,535 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 350.700 LY (107.518 pc) |