K2-189 c
Astrophysical Synthesis & Habitability Characterization
K2-189 c is a confirmed sub-neptune exoplanet orbiting the star K2-189, located approximately 789.7 light-years (242.11 parsecs) from the Solar System. First announced in 2018 by K2 using the Transit detection technique (producing an estimated primary transit depth of 0.058% across the stellar disk), this world measures 2.31 Earth radii and has a measured mass of 5.95 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 1.12 g⊕ (10.98 m/s²), and an escape velocity of 18 km/s.
In its orbital architecture around K2-189, K2-189 c completes one full revolution every 6.679 Earth days at a semi-major axis of 0.068 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 110.8 km/s (compared to Earth's 29.8 km/s).
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 877 K (+604°C / +1119°F) and receiving 140.00 S⊕ (~190,540 W/m²), K2-189 c orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star K2-189 is classified as a stellar host with an effective photospheric temperature of 5,442 K, a radius of 0.879 R☉, a mass of 0.85 M☉, an estimated bolometric luminosity of 0.608 L☉. Stellar evolution modeling indicates a metallicity of [Fe/H] = -0.1 dex (near-solar heavy-element abundance). From Earth, K2-189 shines at apparent V-band magnitude 12.398 (faint and requiring research-grade or CCD telescopic photometry) in the Southern celestial hemisphere. The K2-189 system is a multi-planet architecture hosting 2 confirmed worlds, with K2-189 c sharing its stellar neighborhood alongside K2-189 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 | K2-189 |
| Spectral Type | Unclassified |
| Effective Temp (Teff) | 5,442 K |
| Stellar Radius | 0.8790 R☉ |
| Stellar Mass | 0.8500 M☉ |
| Bolometric Luminosity | 0.608 L☉ |
| Metallicity [Fe/H] | -0.100 dex |
| Stellar Age | — |
| Apparent Magnitude | V: 12.398 · G: 12.254 |
| System Architecture | 1 Star, 2 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.068000 AU |
| Orbital Period | 6.679 days |
| Mean Orbital Velocity | 110.8 km/s |
| Orbital Eccentricity (e) | Circular (0.00) |
| Orbital Inclination (i) | 88.1835° |
| Mean Bulk Density | 2.66 g/cm³ (18 km/s vesc) |
| Insolation Flux | 140.0000 S⊕ (~190,540 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 789.700 LY (242.113 pc) |