K2-3 b
Astrophysical Synthesis & Habitability Characterization
K2-3 b is a confirmed sub-neptune exoplanet orbiting the star K2-3, located approximately 143.7 light-years (44.07 parsecs) from the Solar System. First announced in 2015 by K2 using the Transit detection technique (producing an estimated primary transit depth of 0.1217% across the stellar disk), this world measures 2.078 Earth radii and has a measured mass of 5.11 Earth masses. Combining its mass and radius yields a mean bulk density of 3.14 g/cm³ (an intermediate density indicative of a deep water-ice mantle or dense volatile envelope), a surface gravity of 1.18 g⊕ (11.57 m/s²), and an escape velocity of 17.5 km/s.
In its orbital architecture around K2-3, K2-3 b completes one full revolution every 10.055 Earth days at a semi-major axis of 0.0747 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 80.8 km/s (compared to Earth's 29.8 km/s). Its moderate orbital eccentricity of e = 0.107 carries the world between 0.0667 AU at periapsis and 0.0827 AU at apoapsis, driving measurable seasonal insolation cycles.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 501 K (+228°C / +442°F) and receiving 10.50 S⊕ (~14,291 W/m²), K2-3 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star K2-3 is classified as a low-mass red dwarf of spectral type M V with an effective photospheric temperature of 3,844 K, a radius of 0.546 R☉, a mass of 0.549 M☉, an estimated bolometric luminosity of 0.058 L☉. Stellar evolution modeling indicates an estimated stellar age of 6.9 Gyr and a metallicity of [Fe/H] = -0.157 dex (metal-poor relative to the Sun). From Earth, K2-3 shines at apparent V-band magnitude 12.168 (faint and requiring research-grade or CCD telescopic photometry) in the Southern celestial hemisphere. The K2-3 system is a multi-planet architecture hosting 3 confirmed worlds, with K2-3 b sharing its stellar neighborhood alongside K2-3 c, K2-3 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 | K2-3 |
| Spectral Type | M V |
| Effective Temp (Teff) | 3,844 K |
| Stellar Radius | 0.5460 R☉ |
| Stellar Mass | 0.5490 M☉ |
| Bolometric Luminosity | 0.058 L☉ |
| Metallicity [Fe/H] | -0.157 dex |
| Stellar Age | 6.900 Gyr |
| Apparent Magnitude | V: 12.168 · G: 11.479 |
| System Architecture | 1 Star, 3 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.074700 AU |
| Orbital Period | 10.055 days |
| Mean Orbital Velocity | 80.8 km/s |
| Orbital Eccentricity (e) | 0.10700 |
| Orbital Inclination (i) | 89.4000° |
| Mean Bulk Density | 3.14 g/cm³ (17.5 km/s vesc) |
| Insolation Flux | 10.5000 S⊕ (~14,291 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 143.700 LY (44.073 pc) |