K2-111 c
Astrophysical Synthesis & Habitability Characterization
K2-111 c is a confirmed sub-neptune exoplanet orbiting the star K2-111, located approximately 653.6 light-years (200.39 parsecs) from the Solar System. First announced in 2020 by Multiple Observatories using the Radial Velocity detection technique (measuring periodic Doppler reflex motion in the host star's spectrum), this world measures 3.34 Earth radii (0.3 Jupiter radii) and has a measured mass of 11.1 Earth masses. Combining its mass and radius yields a mean bulk density of 1.64 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 20.4 km/s.
In its orbital architecture around K2-111, K2-111 c completes one full revolution every 15.675 Earth days at a semi-major axis of 0.11565 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 80.3 km/s (compared to Earth's 29.8 km/s). Its moderate orbital eccentricity of e = 0.069 carries the world between 0.1077 AU at periapsis and 0.1236 AU at apoapsis, driving measurable seasonal insolation cycles.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 923 K (+650°C / +1202°F) and receiving 142.06 S⊕ (~193,339 W/m²), K2-111 c orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star K2-111 is classified as a solar-type yellow star of spectral type G2 with an effective photospheric temperature of 5,775 K, a radius of 1.25 R☉, a mass of 0.84 M☉, an estimated bolometric luminosity of 1.559 L☉. Stellar evolution modeling indicates an estimated stellar age of 12.3 Gyr and a metallicity of [Fe/H] = -0.46 dex (metal-poor relative to the Sun). From Earth, K2-111 shines at apparent V-band magnitude 11.13 (faint and requiring research-grade or CCD telescopic photometry) in the Northern celestial hemisphere. The K2-111 system is a multi-planet architecture hosting 2 confirmed worlds, with K2-111 c sharing its stellar neighborhood alongside K2-111 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: Multiple Observatories · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | K2-111 |
| Spectral Type | G2 |
| Effective Temp (Teff) | 5,775 K |
| Stellar Radius | 1.2500 R☉ |
| Stellar Mass | 0.8400 M☉ |
| Bolometric Luminosity | 1.559 L☉ |
| Metallicity [Fe/H] | -0.460 dex |
| Stellar Age | 12.300 Gyr |
| Apparent Magnitude | V: 11.130 · G: 10.929 |
| System Architecture | 1 Star, 2 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.115650 AU |
| Orbital Period | 15.675 days |
| Mean Orbital Velocity | 80.3 km/s |
| Orbital Eccentricity (e) | 0.06900 |
| Orbital Inclination (i) | — |
| Mean Bulk Density | 1.64 g/cm³ (20.4 km/s vesc) |
| Insolation Flux | 142.0569 S⊕ (~193,339 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 653.600 LY (200.394 pc) |