HD 155358 b
Astrophysical Synthesis & Habitability Characterization
HD 155358 b is a confirmed gas giant exoplanet orbiting the star HD 155358, located approximately 142.3 light-years (43.62 parsecs) from the Solar System. First announced in 2007 by McDonald Observatory using the Radial Velocity detection technique (measuring periodic Doppler reflex motion in the host star's spectrum), this world measures 13.8 Earth radii (1.23 Jupiter radii) and has a measured mass of 314.652 Earth masses (0.99 Jupiter masses). Combining its mass and radius yields a mean bulk density of 0.66 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 1.65 g⊕ (16.18 m/s²), and an escape velocity of 53.4 km/s.
In its orbital architecture around HD 155358, HD 155358 b completes one full revolution every 194.3 Earth days at a semi-major axis of 0.63 AU (situated at an orbital separation between Mercury's 0.39 AU and Venus's 0.72 AU). Its mean orbital velocity is approximately 35.3 km/s (compared to Earth's 29.8 km/s). Its moderate orbital eccentricity of e = 0.17 carries the world between 0.5229 AU at periapsis and 0.7371 AU at apoapsis, driving measurable seasonal insolation cycles.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 421 K (+148°C / +298°F) and receiving 5.02 S⊕ (~6,834 W/m²), HD 155358 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star HD 155358 is classified as a solar-type yellow star of spectral type G0 with an effective photospheric temperature of 5,905 K, a radius of 1.38 R☉, a mass of 1.15 M☉, an estimated bolometric luminosity of 2.077 L☉. Stellar evolution modeling indicates an estimated stellar age of 10.7 Gyr and a metallicity of [Fe/H] = -0.6 dex (metal-poor relative to the Sun). From Earth, HD 155358 shines at apparent V-band magnitude 7.28 (accessible to binoculars and small amateur telescopes) in the Northern celestial hemisphere. The HD 155358 system is a multi-planet architecture hosting 2 confirmed worlds, with HD 155358 b sharing its stellar neighborhood alongside HD 155358 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: McDonald Observatory · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | HD 155358 |
| Spectral Type | G0 |
| Effective Temp (Teff) | 5,905 K |
| Stellar Radius | 1.3800 R☉ |
| Stellar Mass | 1.1500 M☉ |
| Bolometric Luminosity | 2.077 L☉ |
| Metallicity [Fe/H] | -0.600 dex |
| Stellar Age | 10.700 Gyr |
| Apparent Magnitude | V: 7.280 · G: 7.121 |
| System Architecture | 1 Star, 2 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.630000 AU |
| Orbital Period | 194.3 days |
| Mean Orbital Velocity | 35.3 km/s |
| Orbital Eccentricity (e) | 0.17000 |
| Orbital Inclination (i) | — |
| Mean Bulk Density | 0.66 g/cm³ (53.4 km/s vesc) |
| Insolation Flux | 5.0212 S⊕ (~6,834 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 142.300 LY (43.620 pc) |