TOI-199 c
Astrophysical Synthesis & Habitability Characterization
TOI-199 c is a confirmed gas giant exoplanet orbiting the star TOI-199, located approximately 333.6 light-years (102.27 parsecs) from the Solar System. First announced in 2023 by Multiple Observatories using the Transit Timing Variations detection technique (producing an estimated primary transit depth of 1.6245% across the stellar disk), this world measures 11.4 Earth radii (1.02 Jupiter radii) and has a measured mass of 88.992 Earth masses (0.28 Jupiter masses). Combining its mass and radius yields a mean bulk density of 0.33 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 0.68 g⊕ (6.67 m/s²), and an escape velocity of 31.3 km/s.
In its orbital architecture around TOI-199, TOI-199 c completes one full revolution every 273.69 Earth days at a semi-major axis of 0.807 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 32.1 km/s (compared to Earth's 29.8 km/s). Its moderate orbital eccentricity of e = 0.096 carries the world between 0.7295 AU at periapsis and 0.8845 AU at apoapsis, driving measurable seasonal insolation cycles.
☁️ Atmospheric Regime (Volatile / Gas Envelope): With a radius of 11.400 R⊕, TOI-199 c exceeds the empirical ~1.8–2.2 R⊕ Fulton radius valley threshold, indicating a substantial hydrogen-helium or supercritical volatile envelope without a conventional solid terrestrial surface.
The host star TOI-199 is classified as a solar-type yellow star of spectral type G9 V with an effective photospheric temperature of 5,255 K, a radius of 0.82 R☉, a mass of 0.936 M☉, an estimated bolometric luminosity of 0.46 L☉. Stellar evolution modeling indicates an estimated stellar age of 0.8 Gyr and a metallicity of [Fe/H] = 0.22 dex (metal-rich relative to the Sun). From Earth, TOI-199 shines at apparent V-band magnitude 10.701 (faint and requiring research-grade or CCD telescopic photometry) in the Southern celestial hemisphere. The TOI-199 system is a multi-planet architecture hosting 2 confirmed worlds, with TOI-199 c sharing its stellar neighborhood alongside TOI-199 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 | TOI-199 |
| Spectral Type | G9 V |
| Effective Temp (Teff) | 5,255 K |
| Stellar Radius | 0.8200 R☉ |
| Stellar Mass | 0.9360 M☉ |
| Bolometric Luminosity | 0.46 L☉ |
| Metallicity [Fe/H] | 0.220 dex |
| Stellar Age | 0.800 Gyr |
| Apparent Magnitude | V: 10.701 · G: 10.578 |
| System Architecture | 1 Star, 2 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.807000 AU |
| Orbital Period | 273.69 days |
| Mean Orbital Velocity | 32.1 km/s |
| Orbital Eccentricity (e) | 0.09600 |
| Orbital Inclination (i) | 90.0000° |
| Mean Bulk Density | 0.33 g/cm³ (31.3 km/s vesc) |
| Insolation Flux | 0.7048 S⊕ (~959 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 333.600 LY (102.270 pc) |