K2-204 b
Astrophysical Synthesis & Habitability Characterization
K2-204 b is a confirmed sub-neptune exoplanet orbiting the star K2-204, located approximately 1882.7 light-years (577.24 parsecs) from the Solar System. First announced in 2018 by K2 using the Transit detection technique (producing an estimated primary transit depth of 0.0539% across the stellar disk), this world measures 3.172 Earth radii (0.28 Jupiter radii) and has a measured mass of 10.2 Earth masses. Combining its mass and radius yields a mean bulk density of 1.76 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 1.01 g⊕ (9.9 m/s²), and an escape velocity of 20.1 km/s.
In its orbital architecture around K2-204, K2-204 b completes one full revolution every 7.056 Earth days at a semi-major axis of 0.0738 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 113.8 km/s (compared to Earth's 29.8 km/s). The planet follows a highly eccentric trajectory (e = 0.28, swinging from 0.0531 AU at periapsis out to 0.0945 AU at apoapsis), pointing to past dynamical scattering or secular gravitational perturbations.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 1148 K (+875°C / +1607°F) and receiving 290.10 S⊕ (~394,823 W/m²), K2-204 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star K2-204 is classified as a stellar host with an effective photospheric temperature of 5,783 K, a radius of 1.253 R☉, a mass of 1.076 M☉, an estimated bolometric luminosity of 1.575 L☉. Stellar evolution modeling indicates an estimated stellar age of 6.5 Gyr and a metallicity of [Fe/H] = 0.21 dex (metal-rich relative to the Sun). From Earth, K2-204 shines at apparent V-band magnitude 12.985 (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 | K2-204 |
| Spectral Type | Unclassified |
| Effective Temp (Teff) | 5,783 K |
| Stellar Radius | 1.2530 R☉ |
| Stellar Mass | 1.0760 M☉ |
| Bolometric Luminosity | 1.575 L☉ |
| Metallicity [Fe/H] | 0.210 dex |
| Stellar Age | 6.500 Gyr |
| Apparent Magnitude | V: 12.985 · G: 12.889 |
| System Architecture | 1 Star, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.073800 AU |
| Orbital Period | 7.056 days |
| Mean Orbital Velocity | 113.8 km/s |
| Orbital Eccentricity (e) | 0.28000 |
| Orbital Inclination (i) | 88.7600° |
| Mean Bulk Density | 1.76 g/cm³ (20.1 km/s vesc) |
| Insolation Flux | 290.0978 S⊕ (~394,823 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 1882.700 LY (577.235 pc) |