K2-99 b
Astrophysical Synthesis & Habitability Characterization
K2-99 b is a confirmed gas giant exoplanet orbiting the star K2-99, located approximately 1693.5 light-years (519.23 parsecs) from the Solar System. First announced in 2016 by K2 using the Transit detection technique (producing an estimated primary transit depth of 0.1825% across the stellar disk), this world measures 11.882 Earth radii (1.06 Jupiter radii) and has a measured mass of 276.511 Earth masses (0.87 Jupiter masses). Combining its mass and radius yields a mean bulk density of 0.91 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 1.96 g⊕ (19.22 m/s²), and an escape velocity of 54 km/s.
In its orbital architecture around K2-99, K2-99 b completes one full revolution every 18.248 Earth days at a semi-major axis of 0.153 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 91.2 km/s (compared to Earth's 29.8 km/s). Its moderate orbital eccentricity of e = 0.22 carries the world between 0.1193 AU at periapsis and 0.1867 AU at apoapsis, driving measurable seasonal insolation cycles.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 1184 K (+911°C / +1672°F) and receiving 357.00 S⊕ (~485,877 W/m²), K2-99 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star K2-99 is classified as a solar-type yellow star of spectral type G0 IV with an effective photospheric temperature of 6,069 K, a radius of 2.55 R☉, a mass of 1.44 M☉, an estimated bolometric luminosity of 7.915 L☉. Stellar evolution modeling indicates an estimated stellar age of 3.7 Gyr and a metallicity of [Fe/H] = 0.2 dex (metal-rich relative to the Sun). From Earth, K2-99 shines at apparent V-band magnitude 11.149 (faint and requiring research-grade or CCD telescopic photometry) in the Southern celestial hemisphere. The K2-99 system is a multi-planet architecture hosting 2 confirmed worlds, with K2-99 b sharing its stellar neighborhood alongside K2-99 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 | K2-99 |
| Spectral Type | G0 IV |
| Effective Temp (Teff) | 6,069 K |
| Stellar Radius | 2.5500 R☉ |
| Stellar Mass | 1.4400 M☉ |
| Bolometric Luminosity | 7.915 L☉ |
| Metallicity [Fe/H] | 0.200 dex |
| Stellar Age | 3.700 Gyr |
| Apparent Magnitude | V: 11.149 · G: 10.949 |
| System Architecture | 1 Star, 2 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.153000 AU |
| Orbital Period | 18.248 days |
| Mean Orbital Velocity | 91.2 km/s |
| Orbital Eccentricity (e) | 0.22000 |
| Orbital Inclination (i) | 88.6000° |
| Mean Bulk Density | 0.91 g/cm³ (54 km/s vesc) |
| Insolation Flux | 357.0000 S⊕ (~485,877 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 1693.500 LY (519.229 pc) |