K2-71 b
Astrophysical Synthesis & Habitability Characterization
K2-71 b is a confirmed sub-neptune exoplanet orbiting the star K2-71, located approximately 499.6 light-years (153.19 parsecs) from the Solar System. First announced in 2016 by K2 using the Transit detection technique (producing an estimated primary transit depth of 0.2141% across the stellar disk), this world measures 2.15 Earth radii and has a measured mass of 5.27 Earth masses. Combining its mass and radius yields a mean bulk density of 2.92 g/cm³ (an intermediate density indicative of a deep water-ice mantle or dense volatile envelope), a surface gravity of 1.14 g⊕ (11.18 m/s²), and an escape velocity of 17.5 km/s.
In its orbital architecture around K2-71, K2-71 b completes one full revolution every 6.985 Earth days at a semi-major axis of 0.0559 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 87.1 km/s (compared to Earth's 29.8 km/s).
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 533 K (+260°C / +500°F) and receiving 13.40 S⊕ (~18,237 W/m²), K2-71 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star K2-71 is classified as a stellar host with an effective photospheric temperature of 4,006 K, a radius of 0.426 R☉, a mass of 0.477 M☉, an estimated bolometric luminosity of 0.042 L☉. From Earth, K2-71 shines at apparent V-band magnitude 16.14 (faint and requiring research-grade or CCD telescopic photometry) in the Southern 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 | K2-71 |
| Spectral Type | Unclassified |
| Effective Temp (Teff) | 4,006 K |
| Stellar Radius | 0.4260 R☉ |
| Stellar Mass | 0.4770 M☉ |
| Bolometric Luminosity | 0.042 L☉ |
| Metallicity [Fe/H] | — |
| Stellar Age | — |
| Apparent Magnitude | V: 16.140 · G: 15.189 |
| System Architecture | 1 Star, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.055900 AU |
| Orbital Period | 6.985 days |
| Mean Orbital Velocity | 87.1 km/s |
| Orbital Eccentricity (e) | Circular (0.00) |
| Orbital Inclination (i) | — |
| Mean Bulk Density | 2.92 g/cm³ (17.5 km/s vesc) |
| Insolation Flux | 13.4000 S⊕ (~18,237 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 499.600 LY (153.192 pc) |