K2-243 b
Astrophysical Synthesis & Habitability Characterization
K2-243 b is a confirmed sub-neptune exoplanet orbiting the star K2-243, located approximately 870.4 light-years (266.86 parsecs) from the Solar System. First announced in 2018 by K2 using the Transit detection technique (producing an estimated primary transit depth of 0.0205% across the stellar disk), this world measures 2.17 Earth radii and has a measured mass of 5.35 Earth masses. Combining its mass and radius yields a mean bulk density of 2.89 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 17.6 km/s.
In its orbital architecture around K2-243, K2-243 b completes one full revolution every 11.542 Earth days at a semi-major axis of 0.1087 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 102.5 km/s (compared to Earth's 29.8 km/s).
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 1035 K (+762°C / +1404°F) and receiving 226.10 S⊕ (~307,715 W/m²), K2-243 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star K2-243 is classified as a stellar host with an effective photospheric temperature of 6,570 K, a radius of 1.39 R☉, a mass of 1.29 M☉, an estimated bolometric luminosity of 3.23 L☉. Stellar evolution modeling indicates a metallicity of [Fe/H] = -0.03 dex (near-solar heavy-element abundance). From Earth, K2-243 shines at apparent V-band magnitude 10.971 (faint and requiring research-grade or CCD telescopic photometry) in the Southern celestial hemisphere. The K2-243 system is a multi-planet architecture hosting 2 confirmed worlds, with K2-243 b sharing its stellar neighborhood alongside K2-243 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 | K2-243 |
| Spectral Type | Unclassified |
| Effective Temp (Teff) | 6,570 K |
| Stellar Radius | 1.3900 R☉ |
| Stellar Mass | 1.2900 M☉ |
| Bolometric Luminosity | 3.23 L☉ |
| Metallicity [Fe/H] | -0.030 dex |
| Stellar Age | — |
| Apparent Magnitude | V: 10.971 · G: 10.742 |
| System Architecture | 1 Star, 2 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.108700 AU |
| Orbital Period | 11.542 days |
| Mean Orbital Velocity | 102.5 km/s |
| Orbital Eccentricity (e) | Circular (0.00) |
| Orbital Inclination (i) | — |
| Mean Bulk Density | 2.89 g/cm³ (17.6 km/s vesc) |
| Insolation Flux | 226.0950 S⊕ (~307,715 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 870.400 LY (266.864 pc) |