K2-43 b
Astrophysical Synthesis & Habitability Characterization
K2-43 b is a confirmed sub-neptune exoplanet orbiting the star K2-43, located approximately 595.4 light-years (182.54 parsecs) from the Solar System. First announced in 2016 by K2 using the Transit detection technique (producing an estimated primary transit depth of 0.582% across the stellar disk), this world measures 4.51 Earth radii (0.4 Jupiter radii) and has a measured mass of 18.5 Earth masses. Combining its mass and radius yields a mean bulk density of 1.11 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 0.91 g⊕ (8.92 m/s²), and an escape velocity of 22.7 km/s.
In its orbital architecture around K2-43, K2-43 b completes one full revolution every 3.471 Earth days at a semi-major axis of 0.03784 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 118.6 km/s (compared to Earth's 29.8 km/s). Its moderate orbital eccentricity of e = 0.07 carries the world between 0.0352 AU at periapsis and 0.0405 AU at apoapsis, driving measurable seasonal insolation cycles.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 939 K (+666°C / +1231°F) and receiving 49.00 S⊕ (~66,689 W/m²), K2-43 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star K2-43 is classified as a stellar host with an effective photospheric temperature of 3,841 K, a radius of 0.542 R☉, a mass of 0.571 M☉, an estimated bolometric luminosity of 0.057 L☉. From Earth, K2-43 shines at apparent V-band magnitude 15.748 (faint and requiring research-grade or CCD telescopic photometry) in the Southern celestial hemisphere. The K2-43 system is a multi-planet architecture hosting 2 confirmed worlds, with K2-43 b sharing its stellar neighborhood alongside K2-43 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 | K2-43 |
| Spectral Type | Unclassified |
| Effective Temp (Teff) | 3,841 K |
| Stellar Radius | 0.5420 R☉ |
| Stellar Mass | 0.5710 M☉ |
| Bolometric Luminosity | 0.057 L☉ |
| Metallicity [Fe/H] | — |
| Stellar Age | — |
| Apparent Magnitude | V: 15.748 · G: 14.822 |
| System Architecture | 1 Star, 2 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.037840 AU |
| Orbital Period | 3.471 days |
| Mean Orbital Velocity | 118.6 km/s |
| Orbital Eccentricity (e) | 0.07000 |
| Orbital Inclination (i) | 89.6000° |
| Mean Bulk Density | 1.11 g/cm³ (22.7 km/s vesc) |
| Insolation Flux | 49.0000 S⊕ (~66,689 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 595.400 LY (182.536 pc) |