K2-136 c
Astrophysical Synthesis & Habitability Characterization
K2-136 c is a confirmed sub-neptune exoplanet orbiting the star K2-136, located approximately 193.2 light-years (59.25 parsecs) from the Solar System. First announced in 2017 by K2 using the Transit detection technique (producing an estimated primary transit depth of 0.165% across the stellar disk), this world measures 3 Earth radii (0.27 Jupiter radii) and has a measured mass of 18.1 Earth masses. Combining its mass and radius yields a mean bulk density of 3.7 g/cm³ (an intermediate density indicative of a deep water-ice mantle or dense volatile envelope), a surface gravity of 2.01 g⊕ (19.71 m/s²), and an escape velocity of 27.5 km/s.
In its orbital architecture around K2-136, K2-136 c completes one full revolution every 17.307 Earth days at a semi-major axis of 0.1185 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 74.5 km/s (compared to Earth's 29.8 km/s). With a near-circular eccentricity of e = 0.047 (ranging from 0.1129 AU at periapsis to 0.1241 AU at apoapsis), the planet experiences minimal orbital distance variation.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 470 K (+197°C / +387°F) and receiving 11.91 S⊕ (~16,210 W/m²), K2-136 c orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star K2-136 is classified as an orange K-type star of spectral type K5 V with an effective photospheric temperature of 4,500 K, a radius of 0.677 R☉, a mass of 0.742 M☉, an estimated bolometric luminosity of 0.169 L☉. Stellar evolution modeling indicates an estimated stellar age of 0.65 Gyr and a metallicity of [Fe/H] = -0.02 dex (near-solar heavy-element abundance). From Earth, K2-136 shines at apparent V-band magnitude 11.101 (faint and requiring research-grade or CCD telescopic photometry) in the Northern celestial hemisphere. The K2-136 system is a multi-planet architecture hosting 3 confirmed worlds, with K2-136 c sharing its stellar neighborhood alongside K2-136 b, K2-136 d.
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 | K2-136 |
| Spectral Type | K5 V |
| Effective Temp (Teff) | 4,500 K |
| Stellar Radius | 0.6770 R☉ |
| Stellar Mass | 0.7420 M☉ |
| Bolometric Luminosity | 0.169 L☉ |
| Metallicity [Fe/H] | -0.020 dex |
| Stellar Age | 0.650 Gyr |
| Apparent Magnitude | V: 11.101 · G: 10.855 |
| System Architecture | 2 Stars, 3 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.118500 AU |
| Orbital Period | 17.307 days |
| Mean Orbital Velocity | 74.5 km/s |
| Orbital Eccentricity (e) | 0.04700 |
| Orbital Inclination (i) | 89.7000° |
| Mean Bulk Density | 3.7 g/cm³ (27.5 km/s vesc) |
| Insolation Flux | 11.9100 S⊕ (~16,210 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 193.200 LY (59.247 pc) |