K2-281 b
Astrophysical Synthesis & Habitability Characterization
K2-281 b is a confirmed gas giant exoplanet orbiting the star K2-281, located approximately 1494.2 light-years (458.14 parsecs) from the Solar System. First announced in 2018 by K2 using the Transit detection technique (producing an estimated primary transit depth of 0.9737% across the stellar disk), this world measures 8.18 Earth radii (0.73 Jupiter radii) and has a measured mass of 50.9 Earth masses (0.16 Jupiter masses). Combining its mass and radius yields a mean bulk density of 0.51 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 0.76 g⊕ (7.45 m/s²), and an escape velocity of 27.9 km/s.
In its orbital architecture around K2-281, K2-281 b completes one full revolution every 8.688 Earth days at a semi-major axis of 0.0773 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 96.8 km/s (compared to Earth's 29.8 km/s).
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 665 K (+392°C / +738°F) and receiving 37.74 S⊕ (~51,362 W/m²), K2-281 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star K2-281 is classified as a stellar host with an effective photospheric temperature of 4,812 K, a radius of 0.76 R☉, a mass of 0.82 M☉, an estimated bolometric luminosity of 0.278 L☉. Stellar evolution modeling indicates a metallicity of [Fe/H] = 0.22 dex (metal-rich relative to the Sun). From Earth, K2-281 shines at apparent V-band magnitude 15.048 (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 | K2-281 |
| Spectral Type | Unclassified |
| Effective Temp (Teff) | 4,812 K |
| Stellar Radius | 0.7600 R☉ |
| Stellar Mass | 0.8200 M☉ |
| Bolometric Luminosity | 0.278 L☉ |
| Metallicity [Fe/H] | 0.220 dex |
| Stellar Age | — |
| Apparent Magnitude | V: 15.048 · G: 14.768 |
| System Architecture | 1 Star, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.077300 AU |
| Orbital Period | 8.688 days |
| Mean Orbital Velocity | 96.8 km/s |
| Orbital Eccentricity (e) | Circular (0.00) |
| Orbital Inclination (i) | — |
| Mean Bulk Density | 0.51 g/cm³ (27.9 km/s vesc) |
| Insolation Flux | 37.7384 S⊕ (~51,362 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 1494.200 LY (458.139 pc) |