HD 120084 b
Astrophysical Synthesis & Habitability Characterization
HD 120084 b is a confirmed gas giant exoplanet orbiting the star HD 120084, located approximately 336.1 light-years (103.04 parsecs) from the Solar System. First announced in 2013 by Okayama Astrophysical Observatory using the Radial Velocity detection technique (measuring periodic Doppler reflex motion in the host star's spectrum), this world measures 12.7 Earth radii (1.13 Jupiter radii) and has a measured mass of 2034.102 Earth masses (6.4 Jupiter masses). Combining its mass and radius yields a mean bulk density of 5.48 g/cm³ (a terrestrial silicate-iron composition comparable to Earth (5.51 g/cm³)), a surface gravity of 12.61 g⊕ (123.66 m/s²), and an escape velocity of 141.6 km/s.
In its orbital architecture around HD 120084, HD 120084 b completes one full revolution every 2142 Earth days (5.86Julian years) at a semi-major axis of 4.21 AU (corresponding to the middle-system regime between Mars at 1.52 AU and Jupiter at 5.20 AU). Its mean orbital velocity is approximately 21.4 km/s (compared to Earth's 29.8 km/s). The planet follows a highly eccentric trajectory (e = 0.483, swinging from 2.1766 AU at periapsis out to 6.2434 AU at apoapsis), pointing to past dynamical scattering or secular gravitational perturbations.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 369 K (+96°C / +205°F) and receiving 3.09 S⊕ (~4,199 W/m²), HD 120084 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star HD 120084 is classified as a solar-type yellow star of spectral type G7 III with an effective photospheric temperature of 4,879 K, a radius of 10.37 R☉, a mass of 2.16 M☉, an estimated bolometric luminosity of 54.673 L☉. Stellar evolution modeling indicates an estimated stellar age of 1.02 Gyr and a metallicity of [Fe/H] = 0.1 dex (metal-rich relative to the Sun). From Earth, HD 120084 shines at apparent V-band magnitude 5.907 (visible to the unaided human eye under dark skies) 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: Okayama Astrophysical Observatory · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | HD 120084 |
| Spectral Type | G7 III |
| Effective Temp (Teff) | 4,879 K |
| Stellar Radius | 10.3700 R☉ |
| Stellar Mass | 2.1600 M☉ |
| Bolometric Luminosity | 54.673 L☉ |
| Metallicity [Fe/H] | 0.100 dex |
| Stellar Age | 1.020 Gyr |
| Apparent Magnitude | V: 5.907 · G: 5.652 |
| System Architecture | 1 Star, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 4.210000 AU |
| Orbital Period | 2142 days |
| Mean Orbital Velocity | 21.4 km/s |
| Orbital Eccentricity (e) | 0.48300 |
| Orbital Inclination (i) | 38.0000° |
| Mean Bulk Density | 5.48 g/cm³ (141.6 km/s vesc) |
| Insolation Flux | 3.0851 S⊕ (~4,199 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 336.100 LY (103.044 pc) |