K2-208 b
Astrophysical Synthesis & Habitability Characterization
K2-208 b is a confirmed super-earth exoplanet orbiting the star K2-208, located approximately 837.9 light-years (256.89 parsecs) from the Solar System. First announced in 2018 by K2 using the Transit detection technique (producing an estimated primary transit depth of 0.031% across the stellar disk), this world measures 1.675 Earth radii and has a measured mass of 3.45 Earth masses. Combining its mass and radius yields a mean bulk density of 4.05 g/cm³ (a terrestrial silicate-iron composition comparable to Earth (5.51 g/cm³)), a surface gravity of 1.23 g⊕ (12.06 m/s²), and an escape velocity of 16.1 km/s.
In its orbital architecture around K2-208, K2-208 b completes one full revolution every 4.191 Earth days at a semi-major axis of 0.04878 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 126.6 km/s (compared to Earth's 29.8 km/s). The planet follows a highly eccentric trajectory (e = 0.37, swinging from 0.0307 AU at periapsis out to 0.0668 AU at apoapsis), pointing to past dynamical scattering or secular gravitational perturbations.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 1122 K (+849°C / +1560°F) and receiving 264.34 S⊕ (~359,770 W/m²), K2-208 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star K2-208 is classified as a stellar host with an effective photospheric temperature of 5,500 K, a radius of 0.872 R☉, a mass of 0.881 M☉, an estimated bolometric luminosity of 0.624 L☉. Stellar evolution modeling indicates an estimated stellar age of 6.1 Gyr and a metallicity of [Fe/H] = -0.064 dex (near-solar heavy-element abundance). From Earth, K2-208 shines at apparent V-band magnitude 12.577 (faint and requiring research-grade or CCD telescopic photometry) in the Northern 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 | K2-208 |
| Spectral Type | Unclassified |
| Effective Temp (Teff) | 5,500 K |
| Stellar Radius | 0.8720 R☉ |
| Stellar Mass | 0.8810 M☉ |
| Bolometric Luminosity | 0.624 L☉ |
| Metallicity [Fe/H] | -0.064 dex |
| Stellar Age | 6.100 Gyr |
| Apparent Magnitude | V: 12.577 · G: 12.314 |
| System Architecture | 1 Star, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.048780 AU |
| Orbital Period | 4.191 days |
| Mean Orbital Velocity | 126.6 km/s |
| Orbital Eccentricity (e) | 0.37000 |
| Orbital Inclination (i) | 86.9400° |
| Mean Bulk Density | 4.05 g/cm³ (16.1 km/s vesc) |
| Insolation Flux | 264.3425 S⊕ (~359,770 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 837.900 LY (256.887 pc) |