K2-39 b
Astrophysical Synthesis & Habitability Characterization
K2-39 b is a confirmed gas giant exoplanet orbiting the star K2-39, located approximately 1002.8 light-years (307.47 parsecs) from the Solar System. First announced in 2016 by K2 using the Transit detection technique (producing an estimated primary transit depth of 0.0375% across the stellar disk), this world measures 6.277 Earth radii (0.56 Jupiter radii) and has a measured mass of 28.605 Earth masses. Combining its mass and radius yields a mean bulk density of 0.64 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 0.73 g⊕ (7.16 m/s²), and an escape velocity of 23.9 km/s.
In its orbital architecture around K2-39, K2-39 b completes one full revolution every 4.605 Earth days at a semi-major axis of 0.05708 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 134.8 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 1670 K (+1397°C / +2547°F) and receiving 1,356.00 S⊕ (~1,845,516 W/m²), K2-39 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star K2-39 is classified as a stellar host with an effective photospheric temperature of 4,881 K, a radius of 2.97 R☉, a mass of 0.66 M☉, an estimated bolometric luminosity of 4.492 L☉. Stellar evolution modeling indicates an estimated stellar age of 6.7 Gyr and a metallicity of [Fe/H] = 0.32 dex (metal-rich relative to the Sun). From Earth, K2-39 shines at apparent V-band magnitude 10.831 (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 | K2-39 |
| Spectral Type | Unclassified |
| Effective Temp (Teff) | 4,881 K |
| Stellar Radius | 2.9700 R☉ |
| Stellar Mass | 0.6600 M☉ |
| Bolometric Luminosity | 4.492 L☉ |
| Metallicity [Fe/H] | 0.320 dex |
| Stellar Age | 6.700 Gyr |
| Apparent Magnitude | V: 10.831 · G: 10.596 |
| System Architecture | 1 Star, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.057080 AU |
| Orbital Period | 4.605 days |
| Mean Orbital Velocity | 134.8 km/s |
| Orbital Eccentricity (e) | 0.00000 |
| Orbital Inclination (i) | 80.3900° |
| Mean Bulk Density | 0.64 g/cm³ (23.9 km/s vesc) |
| Insolation Flux | 1356.0000 S⊕ (~1,845,516 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 1002.800 LY (307.470 pc) |