K2-317 b
Astrophysical Synthesis & Habitability Characterization
K2-317 b is a confirmed sub-neptune exoplanet orbiting the star K2-317, located approximately 575 light-years (176.29 parsecs) from the Solar System. First announced in 2020 by K2 using the Transit detection technique (producing an estimated primary transit depth of 0.5023% across the stellar disk), this world measures 2.93 Earth radii and has a measured mass of 8.91 Earth masses. Combining its mass and radius yields a mean bulk density of 1.95 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 1.04 g⊕ (10.2 m/s²), and an escape velocity of 19.5 km/s.
In its orbital architecture around K2-317, K2-317 b completes one full revolution every 6.22 Earth days at a semi-major axis of 0.0542 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 94.8 km/s (compared to Earth's 29.8 km/s).
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 432 K (+159°C / +318°F) and receiving 4.58 S⊕ (~6,240 W/m²), K2-317 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star K2-317 is classified as a stellar host with an effective photospheric temperature of 3,387 K, a radius of 0.379 R☉, a mass of 0.403 M☉, an estimated bolometric luminosity of 0.017 L☉. From Earth, K2-317 shines at apparent V-band magnitude 17.74 (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 | K2-317 |
| Spectral Type | Unclassified |
| Effective Temp (Teff) | 3,387 K |
| Stellar Radius | 0.3790 R☉ |
| Stellar Mass | 0.4030 M☉ |
| Bolometric Luminosity | 0.017 L☉ |
| Metallicity [Fe/H] | — |
| Stellar Age | — |
| Apparent Magnitude | V: 17.740 · G: 16.639 |
| System Architecture | 1 Star, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.054200 AU |
| Orbital Period | 6.22 days |
| Mean Orbital Velocity | 94.8 km/s |
| Orbital Eccentricity (e) | Circular (0.00) |
| Orbital Inclination (i) | 89.2200° |
| Mean Bulk Density | 1.95 g/cm³ (19.5 km/s vesc) |
| Insolation Flux | 4.5848 S⊕ (~6,240 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 575.000 LY (176.291 pc) |