HD 188015 b
Astrophysical Synthesis & Habitability Characterization
HD 188015 b is a confirmed gas giant exoplanet orbiting the star HD 188015, located approximately 165.3 light-years (50.67 parsecs) from the Solar System. First announced in 2004 by W. M. Keck Observatory using the Radial Velocity detection technique (measuring periodic Doppler reflex motion in the host star's spectrum), this world measures 13.6 Earth radii (1.21 Jupiter radii) and has a measured mass of 476.72 Earth masses (1.5 Jupiter masses). Combining its mass and radius yields a mean bulk density of 1.04 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 2.58 g⊕ (25.3 m/s²), and an escape velocity of 66.2 km/s.
In its orbital architecture around HD 188015, HD 188015 b completes one full revolution every 461.2 Earth days (1.26Julian years) at a semi-major axis of 1.203 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 28.4 km/s (compared to Earth's 29.8 km/s). Its moderate orbital eccentricity of e = 0.137 carries the world between 1.0382 AU at periapsis and 1.3678 AU at apoapsis, driving measurable seasonal insolation cycles.
☁️ Atmospheric Regime (Volatile / Gas Envelope): With a radius of 13.600 R⊕, HD 188015 b 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 HD 188015 is classified as a solar-type yellow star of spectral type G5 IV with an effective photospheric temperature of 5,746 K, a radius of 1.1253 R☉, a mass of 1.09 M☉, an estimated bolometric luminosity of 1.238 L☉. Stellar evolution modeling indicates an estimated stellar age of 6.61 Gyr and a metallicity of [Fe/H] = 0.289 dex (metal-rich relative to the Sun). From Earth, HD 188015 shines at apparent V-band magnitude 8.24 (accessible to binoculars and small amateur telescopes) in the Northern 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: W. M. Keck Observatory · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | HD 188015 |
| Spectral Type | G5 IV |
| Effective Temp (Teff) | 5,746 K |
| Stellar Radius | 1.1253 R☉ |
| Stellar Mass | 1.0900 M☉ |
| Bolometric Luminosity | 1.238 L☉ |
| Metallicity [Fe/H] | 0.289 dex |
| Stellar Age | 6.610 Gyr |
| Apparent Magnitude | V: 8.240 · G: 8.066 |
| System Architecture | 2 Stars, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 1.203000 AU |
| Orbital Period | 461.2 days |
| Mean Orbital Velocity | 28.4 km/s |
| Orbital Eccentricity (e) | 0.13700 |
| Orbital Inclination (i) | — |
| Mean Bulk Density | 1.04 g/cm³ (66.2 km/s vesc) |
| Insolation Flux | 0.7914 S⊕ (~1,077 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 165.300 LY (50.671 pc) |