K2-178 b
Astrophysical Synthesis & Habitability Characterization
K2-178 b is a confirmed sub-neptune exoplanet orbiting the star K2-178, located approximately 700.4 light-years (214.75 parsecs) from the Solar System. First announced in 2018 by K2 using the Transit detection technique (producing an estimated primary transit depth of 0.1351% across the stellar disk), this world measures 3.558 Earth radii (0.32 Jupiter radii) and has a measured mass of 12.4 Earth masses. Combining its mass and radius yields a mean bulk density of 1.52 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 0.98 g⊕ (9.61 m/s²), and an escape velocity of 20.9 km/s.
In its orbital architecture around K2-178, K2-178 b completes one full revolution every 8.748 Earth days.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 840 K (+567°C / +1053°F) and receiving 117.83 S⊕ (~160,361 W/m²), K2-178 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star K2-178 is classified as a stellar host with an effective photospheric temperature of 5,525 K, a radius of 0.8873 R☉, a mass of 0.9511 M☉, an estimated bolometric luminosity of 0.658 L☉. Stellar evolution modeling indicates a metallicity of [Fe/H] = 0.09 dex (metal-rich relative to the Sun). From Earth, K2-178 shines at apparent V-band magnitude 12.382 (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 | K2-178 |
| Spectral Type | Unclassified |
| Effective Temp (Teff) | 5,525 K |
| Stellar Radius | 0.8873 R☉ |
| Stellar Mass | 0.9511 M☉ |
| Bolometric Luminosity | 0.658 L☉ |
| Metallicity [Fe/H] | 0.090 dex |
| Stellar Age | — |
| Apparent Magnitude | V: 12.382 · G: 12.156 |
| System Architecture | 1 Star, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | — |
| Orbital Period | 8.748 days |
| Orbital Eccentricity (e) | Circular (0.00) |
| Orbital Inclination (i) | 88.6108° |
| Mean Bulk Density | 1.52 g/cm³ (20.9 km/s vesc) |
| Insolation Flux | 117.8260 S⊕ (~160,361 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 700.400 LY (214.753 pc) |