HD 205158 b
Astrophysical Synthesis & Habitability Characterization
HD 205158 b is a confirmed gas giant exoplanet orbiting the star HD 205158, located approximately 282.5 light-years (86.62 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 13.9 Earth radii (1.24 Jupiter radii) and has a measured mass of 124.589 Earth masses (0.39 Jupiter masses). Combining its mass and radius yields a mean bulk density of 0.26 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 0.64 g⊕ (6.28 m/s²), and an escape velocity of 33.5 km/s.
In its orbital architecture around HD 205158, HD 205158 b completes one full revolution every 25.338 Earth days at a semi-major axis of 0.177 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 76 km/s (compared to Earth's 29.8 km/s). Its moderate orbital eccentricity of e = 0.145 carries the world between 0.1513 AU at periapsis and 0.2027 AU at apoapsis, driving measurable seasonal insolation cycles.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 963 K (+690°C / +1274°F) and receiving 143.45 S⊕ (~195,241 W/m²), HD 205158 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star HD 205158 is classified as a stellar host with an effective photospheric temperature of 6,134 K, a radius of 1.8774 R☉, a mass of 1.16 M☉, an estimated bolometric luminosity of 4.477 L☉. From Earth, HD 205158 shines at apparent V-band magnitude 7.84 (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 205158 |
| Spectral Type | Unclassified |
| Effective Temp (Teff) | 6,134 K |
| Stellar Radius | 1.8774 R☉ |
| Stellar Mass | 1.1600 M☉ |
| Bolometric Luminosity | 4.477 L☉ |
| Metallicity [Fe/H] | — |
| Stellar Age | — |
| Apparent Magnitude | V: 7.840 · G: 7.719 |
| System Architecture | 1 Star, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.177000 AU |
| Orbital Period | 25.338 days |
| Mean Orbital Velocity | 76 km/s |
| Orbital Eccentricity (e) | 0.14500 |
| Orbital Inclination (i) | — |
| Mean Bulk Density | 0.26 g/cm³ (33.5 km/s vesc) |
| Insolation Flux | 143.4540 S⊕ (~195,241 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 282.500 LY (86.616 pc) |