HD 113538 b
Astrophysical Synthesis & Habitability Characterization
HD 113538 b is a confirmed gas giant exoplanet orbiting the star HD 113538, located approximately 53.1 light-years (16.28 parsecs) from the Solar System. First announced in 2010 by La Silla Observatory using the Radial Velocity detection technique (measuring periodic Doppler reflex motion in the host star's spectrum), this world measures 13.2 Earth radii (1.18 Jupiter radii) and has a measured mass of 114.41 Earth masses (0.36 Jupiter masses). Combining its mass and radius yields a mean bulk density of 0.27 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 0.66 g⊕ (6.47 m/s²), and an escape velocity of 32.9 km/s.
In its orbital architecture around HD 113538, HD 113538 b completes one full revolution every 663.2 Earth days (1.82Julian years) at a semi-major axis of 1.24 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 20.3 km/s (compared to Earth's 29.8 km/s). Its moderate orbital eccentricity of e = 0.14 carries the world between 1.0664 AU at periapsis and 1.4136 AU at apoapsis, driving measurable seasonal insolation cycles.
❄️ Thermal Regime (Cryogenic Zone): With an equilibrium temperature of 141 K (-132°C / -206°F) and an incident flux of 0.06 S⊕ (~80 W/m²), surface water and volatile species on HD 113538 b would remain locked in cryogenic ice phases unless warmed by subsurface tidal or radiogenic heating.
The host star HD 113538 is classified as an orange K-type star of spectral type K9 V with an effective photospheric temperature of 4,462 K, a radius of 0.53 R☉, a mass of 0.585 M☉, an estimated bolometric luminosity of 0.1 L☉. Stellar evolution modeling indicates an estimated stellar age of 4.3 Gyr and a metallicity of [Fe/H] = -0.24 dex (metal-poor relative to the Sun). From Earth, HD 113538 shines at apparent V-band magnitude 9.05 (accessible to binoculars and small amateur telescopes) in the Southern celestial hemisphere. The HD 113538 system is a multi-planet architecture hosting 2 confirmed worlds, with HD 113538 b sharing its stellar neighborhood alongside HD 113538 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: La Silla Observatory · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | HD 113538 |
| Spectral Type | K9 V |
| Effective Temp (Teff) | 4,462 K |
| Stellar Radius | 0.5300 R☉ |
| Stellar Mass | 0.5850 M☉ |
| Bolometric Luminosity | 0.1 L☉ |
| Metallicity [Fe/H] | -0.240 dex |
| Stellar Age | 4.300 Gyr |
| Apparent Magnitude | V: 9.050 · G: 8.443 |
| System Architecture | 1 Star, 2 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 1.240000 AU |
| Orbital Period | 663.2 days |
| Mean Orbital Velocity | 20.3 km/s |
| Orbital Eccentricity (e) | 0.14000 |
| Orbital Inclination (i) | — |
| Mean Bulk Density | 0.27 g/cm³ (32.9 km/s vesc) |
| Insolation Flux | 0.0585 S⊕ (~80 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 53.100 LY (16.282 pc) |