K2-154 c
Astrophysical Synthesis & Habitability Characterization
K2-154 c is a confirmed sub-neptune exoplanet orbiting the star K2-154, located approximately 421.9 light-years (129.36 parsecs) from the Solar System. First announced in 2018 by K2 using the Transit detection technique (producing an estimated primary transit depth of 0.0907% across the stellar disk), this world measures 2.07 Earth radii and has a measured mass of 4.94 Earth masses. Combining its mass and radius yields a mean bulk density of 3.07 g/cm³ (an intermediate density indicative of a deep water-ice mantle or dense volatile envelope), a surface gravity of 1.15 g⊕ (11.28 m/s²), and an escape velocity of 17.3 km/s.
In its orbital architecture around K2-154, K2-154 c completes one full revolution every 7.955 Earth days at a semi-major axis of 0.0677 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 92.6 km/s (compared to Earth's 29.8 km/s).
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 552 K (+279°C / +534°F) and receiving 20.50 S⊕ (~27,901 W/m²), K2-154 c orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star K2-154 is classified as a low-mass red dwarf of spectral type M0.0 V with an effective photospheric temperature of 4,097 K, a radius of 0.63 R☉, a mass of 0.65 M☉, an estimated bolometric luminosity of 0.1 L☉. Stellar evolution modeling indicates a metallicity of [Fe/H] = 0.21 dex (metal-rich relative to the Sun). From Earth, K2-154 shines at apparent V-band magnitude 13.861 (faint and requiring research-grade or CCD telescopic photometry) in the Southern celestial hemisphere. The K2-154 system is a multi-planet architecture hosting 2 confirmed worlds, with K2-154 c sharing its stellar neighborhood alongside K2-154 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 | K2-154 |
| Spectral Type | M0.0 V |
| Effective Temp (Teff) | 4,097 K |
| Stellar Radius | 0.6300 R☉ |
| Stellar Mass | 0.6500 M☉ |
| Bolometric Luminosity | 0.1 L☉ |
| Metallicity [Fe/H] | 0.210 dex |
| Stellar Age | — |
| Apparent Magnitude | V: 13.861 · G: 13.317 |
| System Architecture | 1 Star, 2 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.067700 AU |
| Orbital Period | 7.955 days |
| Mean Orbital Velocity | 92.6 km/s |
| Orbital Eccentricity (e) | Circular (0.00) |
| Orbital Inclination (i) | — |
| Mean Bulk Density | 3.07 g/cm³ (17.3 km/s vesc) |
| Insolation Flux | 20.5000 S⊕ (~27,901 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 421.900 LY (129.356 pc) |