K2-181 b
Astrophysical Synthesis & Habitability Characterization
K2-181 b is a confirmed sub-neptune exoplanet orbiting the star K2-181, located approximately 1177.1 light-years (360.91 parsecs) from the Solar System. First announced in 2018 by K2 using the Transit detection technique (producing an estimated primary transit depth of 0.0541% across the stellar disk), this world measures 2.69 Earth radii and has a measured mass of 7.7 Earth masses. Combining its mass and radius yields a mean bulk density of 2.18 g/cm³ (an intermediate density indicative of a deep water-ice mantle or dense volatile envelope), a surface gravity of 1.06 g⊕ (10.4 m/s²), and an escape velocity of 18.9 km/s.
In its orbital architecture around K2-181, K2-181 b completes one full revolution every 6.894 Earth days at a semi-major axis of 0.0706 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 111.4 km/s (compared to Earth's 29.8 km/s). The planet follows a highly eccentric trajectory (e = 0.4, swinging from 0.0424 AU at periapsis out to 0.0988 AU at apoapsis), pointing to past dynamical scattering or secular gravitational perturbations.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 949 K (+676°C / +1249°F) and receiving 192.00 S⊕ (~261,312 W/m²), K2-181 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star K2-181 is classified as a stellar host with an effective photospheric temperature of 5,528 K, a radius of 1.06 R☉, a mass of 0.96 M☉, an estimated bolometric luminosity of 0.941 L☉. Stellar evolution modeling indicates an estimated stellar age of 5.9 Gyr and a metallicity of [Fe/H] = 0.18 dex (metal-rich relative to the Sun). From Earth, K2-181 shines at apparent V-band magnitude 12.669 (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 | K2-181 |
| Spectral Type | Unclassified |
| Effective Temp (Teff) | 5,528 K |
| Stellar Radius | 1.0600 R☉ |
| Stellar Mass | 0.9600 M☉ |
| Bolometric Luminosity | 0.941 L☉ |
| Metallicity [Fe/H] | 0.180 dex |
| Stellar Age | 5.900 Gyr |
| Apparent Magnitude | V: 12.669 · G: 12.562 |
| System Architecture | 1 Star, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.070600 AU |
| Orbital Period | 6.894 days |
| Mean Orbital Velocity | 111.4 km/s |
| Orbital Eccentricity (e) | 0.40000 |
| Orbital Inclination (i) | 87.4000° |
| Mean Bulk Density | 2.18 g/cm³ (18.9 km/s vesc) |
| Insolation Flux | 192.0000 S⊕ (~261,312 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 1177.100 LY (360.911 pc) |