HD 20782 b
Astrophysical Synthesis & Habitability Characterization
HD 20782 b is a confirmed gas giant exoplanet orbiting the star HD 20782, located approximately 117.4 light-years (35.99 parsecs) from the Solar System. First announced in 2006 by Anglo-Australian Telescope using the Radial Velocity detection technique (measuring periodic Doppler reflex motion in the host star's spectrum), this world measures 13.6 Earth radii (1.21 Jupiter radii) and has a measured mass of 472.83 Earth masses (1.49 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 2.56 g⊕ (25.11 m/s²), and an escape velocity of 66 km/s.
In its orbital architecture around HD 20782, HD 20782 b completes one full revolution every 597.064 Earth days (1.63Julian years) at a semi-major axis of 1.3649 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 24.9 km/s (compared to Earth's 29.8 km/s). The planet follows a highly eccentric trajectory (e = 0.95, swinging from 0.0682 AU at periapsis out to 2.6616 AU at apoapsis), pointing to past dynamical scattering or secular gravitational perturbations.
☁️ Atmospheric Regime (Volatile / Gas Envelope): With a radius of 13.600 R⊕, HD 20782 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 20782 is classified as a solar-type yellow star of spectral type G1.5 V with an effective photospheric temperature of 5,782 K, a radius of 1.1268 R☉, a mass of 1.04 M☉, an estimated bolometric luminosity of 1.273 L☉. Stellar evolution modeling indicates an estimated stellar age of 5.53 Gyr and a metallicity of [Fe/H] = -0.054 dex (near-solar heavy-element abundance). From Earth, HD 20782 shines at apparent V-band magnitude 7.36 (accessible to binoculars and small amateur telescopes) in the Southern 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: Anglo-Australian Telescope · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | HD 20782 |
| Spectral Type | G1.5 V |
| Effective Temp (Teff) | 5,782 K |
| Stellar Radius | 1.1268 R☉ |
| Stellar Mass | 1.0400 M☉ |
| Bolometric Luminosity | 1.273 L☉ |
| Metallicity [Fe/H] | -0.054 dex |
| Stellar Age | 5.530 Gyr |
| Apparent Magnitude | V: 7.360 · G: 7.193 |
| System Architecture | 2 Stars, 5 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 1.364900 AU |
| Orbital Period | 597.064 days |
| Mean Orbital Velocity | 24.9 km/s |
| Orbital Eccentricity (e) | 0.95000 |
| Orbital Inclination (i) | — |
| Mean Bulk Density | 1.04 g/cm³ (66 km/s vesc) |
| Insolation Flux | 0.6863 S⊕ (~934 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 117.400 LY (35.986 pc) |