K2-238 b
Astrophysical Synthesis & Habitability Characterization
K2-238 b is a confirmed gas giant exoplanet orbiting the star K2-238, located approximately 1754.6 light-years (537.96 parsecs) from the Solar System. First announced in 2018 by K2 using the Transit detection technique (producing an estimated primary transit depth of 0.706% across the stellar disk), this world measures 14.572 Earth radii (1.3 Jupiter radii) and has a measured mass of 273.334 Earth masses (0.86 Jupiter masses). Combining its mass and radius yields a mean bulk density of 0.49 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 1.29 g⊕ (12.65 m/s²), and an escape velocity of 48.4 km/s.
In its orbital architecture around K2-238, K2-238 b completes one full revolution every 3.205 Earth days at a semi-major axis of 0.046 AU (an ultra-close orbit less than one-seventh of Mercury's 0.387 AU distance from the Sun, where strong stellar tidal forces typically induce synchronous rotation). Its mean orbital velocity is approximately 156.2 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 1587 K (+1314°C / +2397°F) and receiving 1,082.64 S⊕ (~1,473,474 W/m²), K2-238 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star K2-238 is classified as a solar-type yellow star of spectral type G2 V with an effective photospheric temperature of 5,630 K, a radius of 1.59 R☉, a mass of 1.19 M☉, an estimated bolometric luminosity of 2.279 L☉. Stellar evolution modeling indicates an estimated stellar age of 5.63 Gyr and a metallicity of [Fe/H] = 0.34 dex (metal-rich relative to the Sun). From Earth, K2-238 shines at apparent V-band magnitude 13.973 (faint and requiring research-grade or CCD telescopic photometry) in the Southern celestial hemisphere.
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 | K2-238 |
| Spectral Type | G2 V |
| Effective Temp (Teff) | 5,630 K |
| Stellar Radius | 1.5900 R☉ |
| Stellar Mass | 1.1900 M☉ |
| Bolometric Luminosity | 2.279 L☉ |
| Metallicity [Fe/H] | 0.340 dex |
| Stellar Age | 5.630 Gyr |
| Apparent Magnitude | V: 13.973 · G: 13.664 |
| System Architecture | 1 Star, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.046000 AU |
| Orbital Period | 3.205 days |
| Mean Orbital Velocity | 156.2 km/s |
| Orbital Eccentricity (e) | 0.00000 |
| Orbital Inclination (i) | 84.5000° |
| Mean Bulk Density | 0.49 g/cm³ (48.4 km/s vesc) |
| Insolation Flux | 1082.6407 S⊕ (~1,473,474 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 1754.600 LY (537.963 pc) |