K2-229 c
Astrophysical Synthesis & Habitability Characterization
K2-229 c is a confirmed sub-neptune exoplanet orbiting the star K2-229, located approximately 334.5 light-years (102.56 parsecs) from the Solar System. First announced in 2018 by K2 using the Transit detection technique (producing an estimated primary transit depth of 0.0555% across the stellar disk), this world measures 2.03 Earth radii and has a measured mass of 7 Earth masses. Combining its mass and radius yields a mean bulk density of 4.61 g/cm³ (a terrestrial silicate-iron composition comparable to Earth (5.51 g/cm³)), a surface gravity of 1.7 g⊕ (16.67 m/s²), and an escape velocity of 20.8 km/s.
In its orbital architecture around K2-229, K2-229 c completes one full revolution every 8.327 Earth days at a semi-major axis of 0.0769 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 100.5 km/s (compared to Earth's 29.8 km/s). The orbit is modeled as circular (e = 0.00), maintaining a constant stellar distance throughout its year.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 750 K (+477°C / +891°F) and receiving 66.00 S⊕ (~89,826 W/m²), K2-229 c orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star K2-229 is classified as a solar-type yellow star of spectral type G9 with an effective photospheric temperature of 5,315 K, a radius of 0.79 R☉, a mass of 0.87 M☉, an estimated bolometric luminosity of 0.447 L☉. Stellar evolution modeling indicates an estimated stellar age of 5.4 Gyr and a metallicity of [Fe/H] = -0.09 dex (near-solar heavy-element abundance). From Earth, K2-229 shines at apparent V-band magnitude 10.985 (faint and requiring research-grade or CCD telescopic photometry) in the Southern celestial hemisphere. The K2-229 system is a multi-planet architecture hosting 2 confirmed worlds, with K2-229 c sharing its stellar neighborhood alongside K2-229 b.
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 | K2-229 |
| Spectral Type | G9 |
| Effective Temp (Teff) | 5,315 K |
| Stellar Radius | 0.7900 R☉ |
| Stellar Mass | 0.8700 M☉ |
| Bolometric Luminosity | 0.447 L☉ |
| Metallicity [Fe/H] | -0.090 dex |
| Stellar Age | 5.400 Gyr |
| Apparent Magnitude | V: 10.985 · G: 10.786 |
| System Architecture | 1 Star, 2 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.076900 AU |
| Orbital Period | 8.327 days |
| Mean Orbital Velocity | 100.5 km/s |
| Orbital Eccentricity (e) | 0.00000 |
| Orbital Inclination (i) | 87.9400° |
| Mean Bulk Density | 4.61 g/cm³ (20.8 km/s vesc) |
| Insolation Flux | 66.0000 S⊕ (~89,826 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 334.500 LY (102.564 pc) |