K2-38 c
Astrophysical Synthesis & Habitability Characterization
K2-38 c is a confirmed sub-neptune exoplanet orbiting the star K2-38, located approximately 628.5 light-years (192.69 parsecs) from the Solar System. First announced in 2016 by K2 using the Transit detection technique (producing an estimated primary transit depth of 0.0392% across the stellar disk), this world measures 2.29 Earth radii and has a measured mass of 8.3 Earth masses. Combining its mass and radius yields a mean bulk density of 3.81 g/cm³ (an intermediate density indicative of a deep water-ice mantle or dense volatile envelope), a surface gravity of 1.58 g⊕ (15.49 m/s²), and an escape velocity of 21.3 km/s.
In its orbital architecture around K2-38, K2-38 c completes one full revolution every 10.561 Earth days at a semi-major axis of 0.09514 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 98 km/s (compared to Earth's 29.8 km/s). Its moderate orbital eccentricity of e = 0.161 carries the world between 0.0798 AU at periapsis and 0.1105 AU at apoapsis, driving measurable seasonal insolation cycles.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 916 K (+643°C / +1189°F) and receiving 117.00 S⊕ (~159,237 W/m²), K2-38 c orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star K2-38 is classified as a solar-type yellow star of spectral type G2 V with an effective photospheric temperature of 5,731 K, a radius of 1.06 R☉, a mass of 1.03 M☉, an estimated bolometric luminosity of 1.087 L☉. Stellar evolution modeling indicates an estimated stellar age of 6.7 Gyr and a metallicity of [Fe/H] = 0.26 dex (metal-rich relative to the Sun). From Earth, K2-38 shines at apparent V-band magnitude 11.344 (faint and requiring research-grade or CCD telescopic photometry) in the Southern celestial hemisphere. The K2-38 system is a multi-planet architecture hosting 2 confirmed worlds, with K2-38 c sharing its stellar neighborhood alongside K2-38 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 | K2-38 |
| Spectral Type | G2 V |
| Effective Temp (Teff) | 5,731 K |
| Stellar Radius | 1.0600 R☉ |
| Stellar Mass | 1.0300 M☉ |
| Bolometric Luminosity | 1.087 L☉ |
| Metallicity [Fe/H] | 0.260 dex |
| Stellar Age | 6.700 Gyr |
| Apparent Magnitude | V: 11.344 · G: 11.184 |
| System Architecture | 1 Star, 2 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.095140 AU |
| Orbital Period | 10.561 days |
| Mean Orbital Velocity | 98 km/s |
| Orbital Eccentricity (e) | 0.16100 |
| Orbital Inclination (i) | 87.6800° |
| Mean Bulk Density | 3.81 g/cm³ (21.3 km/s vesc) |
| Insolation Flux | 117.0000 S⊕ (~159,237 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 628.500 LY (192.690 pc) |