K2-124 b
Astrophysical Synthesis & Habitability Characterization
K2-124 b is a confirmed sub-neptune exoplanet orbiting the star K2-124, located approximately 457.9 light-years (140.39 parsecs) from the Solar System. First announced in 2017 by K2 using the Transit detection technique (producing an estimated primary transit depth of 0.4695% across the stellar disk), this world measures 2.9 Earth radii and has a measured mass of 8.75 Earth masses. Combining its mass and radius yields a mean bulk density of 1.98 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 1.04 g⊕ (10.2 m/s²), and an escape velocity of 19.4 km/s.
In its orbital architecture around K2-124, K2-124 b completes one full revolution every 6.414 Earth days at a semi-major axis of 0.049 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 83.1 km/s (compared to Earth's 29.8 km/s). Its moderate orbital eccentricity of e = 0.08 carries the world between 0.0451 AU at periapsis and 0.0529 AU at apoapsis, driving measurable seasonal insolation cycles.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 442 K (+169°C / +336°F) and receiving 8.70 S⊕ (~11,841 W/m²), K2-124 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star K2-124 is classified as a stellar host with an effective photospheric temperature of 3,570 K, a radius of 0.388 R☉, a mass of 0.39 M☉, an estimated bolometric luminosity of 0.022 L☉. Stellar evolution modeling indicates a metallicity of [Fe/H] = 0.023 dex (near-solar heavy-element abundance). From Earth, K2-124 shines at apparent V-band magnitude 16.692 (faint and requiring research-grade or CCD telescopic photometry) in the Northern celestial hemisphere.
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 | K2-124 |
| Spectral Type | Unclassified |
| Effective Temp (Teff) | 3,570 K |
| Stellar Radius | 0.3880 R☉ |
| Stellar Mass | 0.3900 M☉ |
| Bolometric Luminosity | 0.022 L☉ |
| Metallicity [Fe/H] | 0.023 dex |
| Stellar Age | — |
| Apparent Magnitude | V: 16.692 · G: 15.462 |
| System Architecture | 1 Star, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.049000 AU |
| Orbital Period | 6.414 days |
| Mean Orbital Velocity | 83.1 km/s |
| Orbital Eccentricity (e) | 0.08000 |
| Orbital Inclination (i) | 89.0300° |
| Mean Bulk Density | 1.98 g/cm³ (19.4 km/s vesc) |
| Insolation Flux | 8.7000 S⊕ (~11,841 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 457.900 LY (140.385 pc) |