K2-24 b
Astrophysical Synthesis & Habitability Characterization
K2-24 b is a confirmed sub-neptune exoplanet orbiting the star K2-24, located approximately 556.3 light-years (170.56 parsecs) from the Solar System. First announced in 2016 by K2 using the Transit detection technique (producing an estimated primary transit depth of 0.1903% across the stellar disk), this world measures 5.638 Earth radii (0.5 Jupiter radii) and has a measured mass of 20.6 Earth masses. Combining its mass and radius yields a mean bulk density of 0.63 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 0.65 g⊕ (6.37 m/s²), and an escape velocity of 21.4 km/s.
In its orbital architecture around K2-24, K2-24 b completes one full revolution every 20.89 Earth days at a semi-major axis of 0.1673 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 87.1 km/s (compared to Earth's 29.8 km/s). With a near-circular eccentricity of e = 0.0498 (ranging from 0.159 AU at periapsis to 0.1756 AU at apoapsis), the planet experiences minimal orbital distance variation.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 732 K (+459°C / +858°F) and receiving 52.00 S⊕ (~70,772 W/m²), K2-24 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star K2-24 is classified as a solar-type yellow star of spectral type G9 V with an effective photospheric temperature of 5,726 K, a radius of 1.185 R☉, a mass of 1.091 M☉, an estimated bolometric luminosity of 1.354 L☉. Stellar evolution modeling indicates an estimated stellar age of 4.9 Gyr and a metallicity of [Fe/H] = 0.41 dex (metal-rich relative to the Sun). From Earth, K2-24 shines at apparent V-band magnitude 11.275 (faint and requiring research-grade or CCD telescopic photometry) in the Southern celestial hemisphere. The K2-24 system is a multi-planet architecture hosting 2 confirmed worlds, with K2-24 b sharing its stellar neighborhood alongside K2-24 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 | K2-24 |
| Spectral Type | G9 V |
| Effective Temp (Teff) | 5,726 K |
| Stellar Radius | 1.1850 R☉ |
| Stellar Mass | 1.0910 M☉ |
| Bolometric Luminosity | 1.354 L☉ |
| Metallicity [Fe/H] | 0.410 dex |
| Stellar Age | 4.900 Gyr |
| Apparent Magnitude | V: 11.275 · G: 10.907 |
| System Architecture | 1 Star, 2 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.167300 AU |
| Orbital Period | 20.89 days |
| Mean Orbital Velocity | 87.1 km/s |
| Orbital Eccentricity (e) | 0.04980 |
| Orbital Inclination (i) | 89.6300° |
| Mean Bulk Density | 0.63 g/cm³ (21.4 km/s vesc) |
| Insolation Flux | 52.0000 S⊕ (~70,772 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 556.300 LY (170.562 pc) |