K2-90 b
Astrophysical Synthesis & Habitability Characterization
K2-90 b is a confirmed sub-neptune exoplanet orbiting the star K2-90, located approximately 437.7 light-years (134.19 parsecs) from the Solar System. First announced in 2016 by K2 using the Transit detection technique (producing an estimated primary transit depth of 0.1483% across the stellar disk), this world measures 2.6 Earth radii and has a measured mass of 7.27 Earth masses. Combining its mass and radius yields a mean bulk density of 2.28 g/cm³ (an intermediate density indicative of a deep water-ice mantle or dense volatile envelope), a surface gravity of 1.08 g⊕ (10.59 m/s²), and an escape velocity of 18.7 km/s.
In its orbital architecture around K2-90, K2-90 b completes one full revolution every 13.733 Earth days at a semi-major axis of 0.096 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 76 km/s (compared to Earth's 29.8 km/s). Its moderate orbital eccentricity of e = 0.07 carries the world between 0.0893 AU at periapsis and 0.1027 AU at apoapsis, driving measurable seasonal insolation cycles.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 502 K (+229°C / +444°F) and receiving 10.20 S⊕ (~13,882 W/m²), K2-90 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star K2-90 is classified as a stellar host with an effective photospheric temperature of 4,484 K, a radius of 0.619 R☉, a mass of 0.629 M☉, an estimated bolometric luminosity of 0.139 L☉. Stellar evolution modeling indicates a metallicity of [Fe/H] = -0.225 dex (metal-poor relative to the Sun). From Earth, K2-90 shines at apparent V-band magnitude 13.707 (faint and requiring research-grade or CCD telescopic photometry) in the Northern celestial hemisphere. The K2-90 system is a multi-planet architecture hosting 2 confirmed worlds, with K2-90 b sharing its stellar neighborhood alongside K2-90 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 | K2-90 |
| Spectral Type | Unclassified |
| Effective Temp (Teff) | 4,484 K |
| Stellar Radius | 0.6190 R☉ |
| Stellar Mass | 0.6290 M☉ |
| Bolometric Luminosity | 0.139 L☉ |
| Metallicity [Fe/H] | -0.225 dex |
| Stellar Age | — |
| Apparent Magnitude | V: 13.707 · G: 13.229 |
| System Architecture | 1 Star, 2 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.096000 AU |
| Orbital Period | 13.733 days |
| Mean Orbital Velocity | 76 km/s |
| Orbital Eccentricity (e) | 0.07000 |
| Orbital Inclination (i) | 89.2400° |
| Mean Bulk Density | 2.28 g/cm³ (18.7 km/s vesc) |
| Insolation Flux | 10.2000 S⊕ (~13,882 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 437.700 LY (134.188 pc) |