K2-209 b
Astrophysical Synthesis & Habitability Characterization
K2-209 b is a confirmed terrestrial exoplanet orbiting the star K2-209, located approximately 249.5 light-years (76.5 parsecs) from the Solar System. First announced in 2018 by K2 using the Transit detection technique (producing an estimated primary transit depth of 0.0125% across the stellar disk), this world measures 0.869 Earth radii and has a measured mass of 0.586 Earth masses. Combining its mass and radius yields a mean bulk density of 4.92 g/cm³ (a terrestrial silicate-iron composition comparable to Earth (5.51 g/cm³)), a surface gravity of 0.78 g⊕ (7.65 m/s²), and an escape velocity of 9.2 km/s.
In its orbital architecture around K2-209, K2-209 b completes one full revolution every 2.081 Earth days.
ℹ️ Thermal & Atmospheric Regime: Current photometric and spectroscopic constraints for K2-209 b place it outside the conservative habitable zone definition pending further atmospheric characterization.
The host star K2-209 is classified as a stellar host with an effective photospheric temperature of 4,720 K, a radius of 0.7124 R☉, a mass of 0.7448 M☉, an estimated bolometric luminosity of 0.226 L☉. Stellar evolution modeling indicates a metallicity of [Fe/H] = -0.06 dex (near-solar heavy-element abundance). From Earth, K2-209 shines at apparent V-band magnitude 11.061 (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 | K2-209 |
| Spectral Type | Unclassified |
| Effective Temp (Teff) | 4,720 K |
| Stellar Radius | 0.7124 R☉ |
| Stellar Mass | 0.7448 M☉ |
| Bolometric Luminosity | 0.226 L☉ |
| Metallicity [Fe/H] | -0.060 dex |
| Stellar Age | — |
| Apparent Magnitude | V: 11.061 · G: 10.745 |
| System Architecture | 1 Star, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | — |
| Orbital Period | 2.081 days |
| Orbital Eccentricity (e) | Circular (0.00) |
| Orbital Inclination (i) | 86.2313° |
| Mean Bulk Density | 4.92 g/cm³ (9.2 km/s vesc) |
| Insolation Flux | — |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 249.500 LY (76.499 pc) |