K2-57 b
Astrophysical Synthesis & Habitability Characterization
K2-57 b is a confirmed sub-neptune exoplanet orbiting the star K2-57, located approximately 861.7 light-years (264.21 parsecs) from the Solar System. First announced in 2016 by K2 using the Transit detection technique (producing an estimated primary transit depth of 0.0995% across the stellar disk), this world measures 2.309 Earth radii and has a measured mass of 5.94 Earth masses. Combining its mass and radius yields a mean bulk density of 2.66 g/cm³ (an intermediate density indicative of a deep water-ice mantle or dense volatile envelope), a surface gravity of 1.11 g⊕ (10.89 m/s²), and an escape velocity of 17.9 km/s.
In its orbital architecture around K2-57, K2-57 b completes one full revolution every 9.007 Earth days at a semi-major axis of 0.0752 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 90.8 km/s (compared to Earth's 29.8 km/s). The planet follows a highly eccentric trajectory (e = 0.25, swinging from 0.0564 AU at periapsis out to 0.094 AU at apoapsis), pointing to past dynamical scattering or secular gravitational perturbations.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 636 K (+363°C / +685°F) and receiving 24.10 S⊕ (~32,800 W/m²), K2-57 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star K2-57 is classified as a stellar host with an effective photospheric temperature of 4,413 K, a radius of 0.671 R☉, a mass of 0.699 M☉, an estimated bolometric luminosity of 0.153 L☉. Stellar evolution modeling indicates an estimated stellar age of 6.8 Gyr and a metallicity of [Fe/H] = 0.08 dex (metal-rich relative to the Sun). From Earth, K2-57 shines at apparent V-band magnitude 14.414 (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 | K2-57 |
| Spectral Type | Unclassified |
| Effective Temp (Teff) | 4,413 K |
| Stellar Radius | 0.6710 R☉ |
| Stellar Mass | 0.6990 M☉ |
| Bolometric Luminosity | 0.153 L☉ |
| Metallicity [Fe/H] | 0.080 dex |
| Stellar Age | 6.800 Gyr |
| Apparent Magnitude | V: 14.414 · G: 14.104 |
| System Architecture | 1 Star, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.075200 AU |
| Orbital Period | 9.007 days |
| Mean Orbital Velocity | 90.8 km/s |
| Orbital Eccentricity (e) | 0.25000 |
| Orbital Inclination (i) | 88.9500° |
| Mean Bulk Density | 2.66 g/cm³ (17.9 km/s vesc) |
| Insolation Flux | 24.1000 S⊕ (~32,800 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 861.700 LY (264.213 pc) |