K2-105 c
Astrophysical Synthesis & Habitability Characterization
K2-105 c is a confirmed sub-neptune exoplanet orbiting the star K2-105, located approximately 645.8 light-years (197.99 parsecs) from the Solar System. First announced in 2026 by Paranal Observatory 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 K2-105, K2-105 c completes one full revolution every 5.022 Earth days at a semi-major axis of 0.0559 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 121.1 km/s (compared to Earth's 29.8 km/s). The orbit is modeled as circular (e = 0.00), maintaining a constant stellar distance throughout its year.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 1037 K (+764°C / +1407°F) and receiving 191.60 S⊕ (~260,768 W/m²), K2-105 c orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star K2-105 is classified as a solar-type yellow star of spectral type G9 V with an effective photospheric temperature of 5,400 K, a radius of 0.887 R☉, a mass of 0.925 M☉, an estimated bolometric luminosity of 0.6 L☉. Stellar evolution modeling indicates an estimated stellar age of 5.1 Gyr and a metallicity of [Fe/H] = 0.16 dex (metal-rich relative to the Sun). From Earth, K2-105 shines at apparent V-band magnitude 11.752 (faint and requiring research-grade or CCD telescopic photometry) in the Northern celestial hemisphere. The K2-105 system is a multi-planet architecture hosting 2 confirmed worlds, with K2-105 c sharing its stellar neighborhood alongside K2-105 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: Paranal Observatory · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | K2-105 |
| Spectral Type | G9 V |
| Effective Temp (Teff) | 5,400 K |
| Stellar Radius | 0.8870 R☉ |
| Stellar Mass | 0.9250 M☉ |
| Bolometric Luminosity | 0.6 L☉ |
| Metallicity [Fe/H] | 0.160 dex |
| Stellar Age | 5.100 Gyr |
| Apparent Magnitude | V: 11.752 · G: 11.712 |
| System Architecture | 1 Star, 2 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.055900 AU |
| Orbital Period | 5.022 days |
| Mean Orbital Velocity | 121.1 km/s |
| Orbital Eccentricity (e) | 0.00000 |
| Orbital Inclination (i) | — |
| Mean Bulk Density | 1.64 g/cm³ (20.4 km/s vesc) |
| Insolation Flux | 191.6000 S⊕ (~260,768 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 645.800 LY (197.989 pc) |