K2-91 b
Astrophysical Synthesis & Habitability Characterization
K2-91 b is a confirmed terrestrial exoplanet orbiting the star K2-91, located approximately 204.1 light-years (62.58 parsecs) from the Solar System. First announced in 2016 by K2 using the Transit detection technique (producing an estimated primary transit depth of 0.1261% across the stellar disk), this world measures 1.1 Earth radii and has a measured mass of 1.37 Earth masses. Combining its mass and radius yields a mean bulk density of 5.68 g/cm³ (a terrestrial silicate-iron composition comparable to Earth (5.51 g/cm³)), a surface gravity of 1.13 g⊕ (11.08 m/s²), and an escape velocity of 12.5 km/s.
In its orbital architecture around K2-91, K2-91 b completes one full revolution every 1.42 Earth days at a semi-major axis of 0.0164 AU (an ultra-close orbit less than one-seventh of Mercury's 0.387 AU distance from the Sun, where strong stellar tidal forces typically induce synchronous rotation). Its mean orbital velocity is approximately 125.7 km/s (compared to Earth's 29.8 km/s). Its moderate orbital eccentricity of e = 0.09 carries the world between 0.0149 AU at periapsis and 0.0179 AU at apoapsis, driving measurable seasonal insolation cycles.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 727 K (+454°C / +849°F) and receiving 46.00 S⊕ (~62,606 W/m²), K2-91 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star K2-91 is classified as a stellar host with an effective photospheric temperature of 3,622 K, a radius of 0.284 R☉, a mass of 0.292 M☉, an estimated bolometric luminosity of 0.012 L☉. From Earth, K2-91 shines at apparent V-band magnitude 15.622 (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 | K2-91 |
| Spectral Type | Unclassified |
| Effective Temp (Teff) | 3,622 K |
| Stellar Radius | 0.2840 R☉ |
| Stellar Mass | 0.2920 M☉ |
| Bolometric Luminosity | 0.012 L☉ |
| Metallicity [Fe/H] | — |
| Stellar Age | — |
| Apparent Magnitude | V: 15.622 · G: 14.322 |
| System Architecture | 1 Star, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.016400 AU |
| Orbital Period | 1.42 days |
| Mean Orbital Velocity | 125.7 km/s |
| Orbital Eccentricity (e) | 0.09000 |
| Orbital Inclination (i) | 88.6200° |
| Mean Bulk Density | 5.68 g/cm³ (12.5 km/s vesc) |
| Insolation Flux | 46.0000 S⊕ (~62,606 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 204.100 LY (62.579 pc) |