HD 136418 b
Astrophysical Synthesis & Habitability Characterization
HD 136418 b is a confirmed gas giant exoplanet orbiting the star HD 136418, located approximately 343 light-years (105.17 parsecs) from the Solar System. First announced in 2009 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 13.3 Earth radii (1.19 Jupiter radii) and has a measured mass of 680.156 Earth masses (2.14 Jupiter masses). Combining its mass and radius yields a mean bulk density of 1.59 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 3.85 g⊕ (37.76 m/s²), and an escape velocity of 80 km/s.
In its orbital architecture around HD 136418, HD 136418 b completes one full revolution every 464.3 Earth days (1.27Julian years) at a semi-major axis of 1.29 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 30.2 km/s (compared to Earth's 29.8 km/s). The planet follows a highly eccentric trajectory (e = 0.25, swinging from 0.9675 AU at periapsis out to 1.6125 AU at apoapsis), pointing to past dynamical scattering or secular gravitational perturbations.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 412 K (+139°C / +282°F) and receiving 4.09 S⊕ (~5,561 W/m²), HD 136418 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star HD 136418 is classified as a solar-type yellow star of spectral type G5 with an effective photospheric temperature of 4,989 K, a radius of 3.78 R☉, a mass of 1.48 M☉, an estimated bolometric luminosity of 7.942 L☉. Stellar evolution modeling indicates an estimated stellar age of 4 Gyr and a metallicity of [Fe/H] = -0.11 dex (metal-poor relative to the Sun). From Earth, HD 136418 shines at apparent V-band magnitude 7.849 (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 136418 |
| Spectral Type | G5 |
| Effective Temp (Teff) | 4,989 K |
| Stellar Radius | 3.7800 R☉ |
| Stellar Mass | 1.4800 M☉ |
| Bolometric Luminosity | 7.942 L☉ |
| Metallicity [Fe/H] | -0.110 dex |
| Stellar Age | 4.000 Gyr |
| Apparent Magnitude | V: 7.849 · G: 7.609 |
| System Architecture | 1 Star, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 1.290000 AU |
| Orbital Period | 464.3 days |
| Mean Orbital Velocity | 30.2 km/s |
| Orbital Eccentricity (e) | 0.25000 |
| Orbital Inclination (i) | — |
| Mean Bulk Density | 1.59 g/cm³ (80 km/s vesc) |
| Insolation Flux | 4.0863 S⊕ (~5,561 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 343.000 LY (105.168 pc) |