HD 154857 b
Astrophysical Synthesis & Habitability Characterization
HD 154857 b is a confirmed gas giant exoplanet orbiting the star HD 154857, located approximately 206.9 light-years (63.45 parsecs) from the Solar System. First announced in 2004 by Anglo-Australian Telescope 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 778.684 Earth masses (2.45 Jupiter masses). Combining its mass and radius yields a mean bulk density of 1.83 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 4.4 g⊕ (43.15 m/s²), and an escape velocity of 85.6 km/s.
In its orbital architecture around HD 154857, HD 154857 b completes one full revolution every 408.6 Earth days (1.12Julian 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 34.3 km/s (compared to Earth's 29.8 km/s). The planet follows a highly eccentric trajectory (e = 0.46, swinging from 0.6966 AU at periapsis out to 1.8834 AU at apoapsis), pointing to past dynamical scattering or secular gravitational perturbations.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 360 K (+87°C / +189°F) and receiving 2.76 S⊕ (~3,762 W/m²), HD 154857 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star HD 154857 is classified as a solar-type yellow star of spectral type G5 V with an effective photospheric temperature of 5,589 K, a radius of 2.3 R☉, a mass of 1.96 M☉, an estimated bolometric luminosity of 4.631 L☉. Stellar evolution modeling indicates an estimated stellar age of 5.64 Gyr and a metallicity of [Fe/H] = -0.22 dex (metal-poor relative to the Sun). From Earth, HD 154857 shines at apparent V-band magnitude 7.24 (accessible to binoculars and small amateur telescopes) in the Southern celestial hemisphere. The HD 154857 system is a multi-planet architecture hosting 2 confirmed worlds, with HD 154857 b sharing its stellar neighborhood alongside HD 154857 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: Anglo-Australian Telescope · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | HD 154857 |
| Spectral Type | G5 V |
| Effective Temp (Teff) | 5,589 K |
| Stellar Radius | 2.3000 R☉ |
| Stellar Mass | 1.9600 M☉ |
| Bolometric Luminosity | 4.631 L☉ |
| Metallicity [Fe/H] | -0.220 dex |
| Stellar Age | 5.640 Gyr |
| Apparent Magnitude | V: 7.240 · G: 7.048 |
| System Architecture | 1 Star, 2 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 1.290000 AU |
| Orbital Period | 408.6 days |
| Mean Orbital Velocity | 34.3 km/s |
| Orbital Eccentricity (e) | 0.46000 |
| Orbital Inclination (i) | — |
| Mean Bulk Density | 1.83 g/cm³ (85.6 km/s vesc) |
| Insolation Flux | 2.7638 S⊕ (~3,762 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 206.900 LY (63.448 pc) |