HD 199509 b
Astrophysical Synthesis & Habitability Characterization
HD 199509 b is a confirmed gas giant exoplanet orbiting the star HD 199509, located approximately 79.3 light-years (24.31 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 7.43 Earth radii (0.66 Jupiter radii) and has a measured mass of 43.225 Earth masses (0.14 Jupiter masses). Combining its mass and radius yields a mean bulk density of 0.58 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 0.78 g⊕ (7.65 m/s²), and an escape velocity of 27 km/s.
In its orbital architecture around HD 199509, HD 199509 b completes one full revolution every 99.622 Earth days at a semi-major axis of 0.426 AU (situated at an orbital separation between Mercury's 0.39 AU and Venus's 0.72 AU). Its mean orbital velocity is approximately 46.5 km/s (compared to Earth's 29.8 km/s). The planet follows a highly eccentric trajectory (e = 0.373, swinging from 0.2671 AU at periapsis out to 0.5849 AU at apoapsis), pointing to past dynamical scattering or secular gravitational perturbations.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 411 K (+138°C / +280°F) and receiving 4.54 S⊕ (~6,178 W/m²), HD 199509 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star HD 199509 is classified as a solar-type yellow star of spectral type G3V with an effective photospheric temperature of 5,796 K, a radius of 0.92 R☉, a mass of 1.04 M☉, an estimated bolometric luminosity of 0.857 L☉. Stellar evolution modeling indicates an estimated stellar age of 1.6 Gyr and a metallicity of [Fe/H] = -0.308 dex (metal-poor relative to the Sun). From Earth, HD 199509 shines at apparent V-band magnitude 6.98 (accessible to binoculars and small amateur telescopes) in the Southern 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: Multiple Observatories · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | HD 199509 |
| Spectral Type | G3V |
| Effective Temp (Teff) | 5,796 K |
| Stellar Radius | 0.9200 R☉ |
| Stellar Mass | 1.0400 M☉ |
| Bolometric Luminosity | 0.857 L☉ |
| Metallicity [Fe/H] | -0.308 dex |
| Stellar Age | 1.600 Gyr |
| Apparent Magnitude | V: 6.980 · G: 6.817 |
| System Architecture | 1 Star, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.426000 AU |
| Orbital Period | 99.622 days |
| Mean Orbital Velocity | 46.5 km/s |
| Orbital Eccentricity (e) | 0.37300 |
| Orbital Inclination (i) | — |
| Mean Bulk Density | 0.58 g/cm³ (27 km/s vesc) |
| Insolation Flux | 4.5393 S⊕ (~6,178 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 79.300 LY (24.306 pc) |