K2-136 d
Astrophysical Synthesis & Habitability Characterization
K2-136 d is a confirmed super-earth 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 0.0449% across the stellar disk), this world measures 1.565 Earth radii and has a measured mass of 3 Earth masses. Combining its mass and radius yields a mean bulk density of 4.32 g/cm³ (a terrestrial silicate-iron composition comparable to Earth (5.51 g/cm³)), a surface gravity of 1.22 g⊕ (11.96 m/s²), and an escape velocity of 15.5 km/s.
In its orbital architecture around K2-136, K2-136 d completes one full revolution every 25.575 Earth days at a semi-major axis of 0.1538 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 65.4 km/s (compared to Earth's 29.8 km/s). Its moderate orbital eccentricity of e = 0.071 carries the world between 0.1429 AU at periapsis and 0.1647 AU at apoapsis, driving measurable seasonal insolation cycles.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 420 K (+147°C / +297°F) and receiving 7.07 S⊕ (~9,622 W/m²), K2-136 d 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 K5.5 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 d sharing its stellar neighborhood alongside K2-136 b, K2-136 c.
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 | K5.5 |
| 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) | 0.153800 AU |
| Orbital Period | 25.575 days |
| Mean Orbital Velocity | 65.4 km/s |
| Orbital Eccentricity (e) | 0.07100 |
| Orbital Inclination (i) | 89.4000° |
| Mean Bulk Density | 4.32 g/cm³ (15.5 km/s vesc) |
| Insolation Flux | 7.0700 S⊕ (~9,622 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 193.200 LY (59.247 pc) |