K2-99 c
Astrophysical Synthesis & Habitability Characterization
K2-99 c 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 2022 by Multiple Observatories using the Radial Velocity detection technique (measuring periodic Doppler reflex motion in the host star's spectrum), this world measures 12.6 Earth radii (1.12 Jupiter radii) and has a measured mass of 2669.759 Earth masses (8.4 Jupiter masses). Combining its mass and radius yields a mean bulk density of 7.36 g/cm³ (an iron-enriched, high-compression rocky core), a surface gravity of 16.82 g⊕ (164.95 m/s²), and an escape velocity of 162.8 km/s.
In its orbital architecture around K2-99, K2-99 c completes one full revolution every 522.2 Earth days (1.43Julian years) at a semi-major axis of 1.43 AU (comparable to the inner terrestrial zone between Venus, Earth at 1.00 AU, and Mars at 1.52 AU). Its mean orbital velocity is approximately 29.8 km/s (compared to Earth's 29.8 km/s). Its moderate orbital eccentricity of e = 0.21 carries the world between 1.1297 AU at periapsis and 1.7303 AU at apoapsis, driving measurable seasonal insolation cycles.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 390 K (+117°C / +243°F) and receiving 3.88 S⊕ (~5,278 W/m²), K2-99 c 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 c sharing its stellar neighborhood alongside K2-99 b.
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: Multiple Observatories · 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) | 1.430000 AU |
| Orbital Period | 522.2 days |
| Mean Orbital Velocity | 29.8 km/s |
| Orbital Eccentricity (e) | 0.21000 |
| Orbital Inclination (i) | — |
| Mean Bulk Density | 7.36 g/cm³ (162.8 km/s vesc) |
| Insolation Flux | 3.8779 S⊕ (~5,278 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 1693.500 LY (519.229 pc) |