K2-19 c
Astrophysical Synthesis & Habitability Characterization
K2-19 c is a confirmed sub-neptune exoplanet orbiting the star K2-19, located approximately 945.3 light-years (289.83 parsecs) from the Solar System. First announced in 2015 by K2 using the Transit detection technique (producing an estimated primary transit depth of 0.2101% across the stellar disk), this world measures 4.1 Earth radii (0.37 Jupiter radii) and has a measured mass of 11 Earth masses. Combining its mass and radius yields a mean bulk density of 0.88 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 0.65 g⊕ (6.37 m/s²), and an escape velocity of 18.3 km/s.
In its orbital architecture around K2-19, K2-19 c completes one full revolution every 11.906 Earth days at a semi-major axis of 0.0982 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 89.7 km/s (compared to Earth's 29.8 km/s). Its moderate orbital eccentricity of e = 0.1 carries the world between 0.0884 AU at periapsis and 0.108 AU at apoapsis, driving measurable seasonal insolation cycles.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 679 K (+406°C / +763°F) and receiving 51.00 S⊕ (~69,411 W/m²), K2-19 c orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star K2-19 is classified as a solar-type yellow star of spectral type G9 with an effective photospheric temperature of 5,322 K, a radius of 0.82 R☉, a mass of 0.88 M☉, an estimated bolometric luminosity of 0.484 L☉. Stellar evolution modeling indicates an estimated stellar age of 1.7 Gyr and a metallicity of [Fe/H] = 0.06 dex (metal-rich relative to the Sun). From Earth, K2-19 shines at apparent V-band magnitude 13.024 (faint and requiring research-grade or CCD telescopic photometry) in the Northern celestial hemisphere. The K2-19 system is a multi-planet architecture hosting 3 confirmed worlds, with K2-19 c sharing its stellar neighborhood alongside K2-19 d, K2-19 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 | K2-19 |
| Spectral Type | G9 |
| Effective Temp (Teff) | 5,322 K |
| Stellar Radius | 0.8200 R☉ |
| Stellar Mass | 0.8800 M☉ |
| Bolometric Luminosity | 0.484 L☉ |
| Metallicity [Fe/H] | 0.060 dex |
| Stellar Age | 1.700 Gyr |
| Apparent Magnitude | V: 13.024 · G: 12.815 |
| System Architecture | 1 Star, 3 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.098200 AU |
| Orbital Period | 11.906 days |
| Mean Orbital Velocity | 89.7 km/s |
| Orbital Eccentricity (e) | 0.10000 |
| Orbital Inclination (i) | 90.0000° |
| Mean Bulk Density | 0.88 g/cm³ (18.3 km/s vesc) |
| Insolation Flux | 51.0000 S⊕ (~69,411 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 945.300 LY (289.827 pc) |