HD 65216 b
Astrophysical Synthesis & Habitability Characterization
HD 65216 b is a confirmed gas giant exoplanet orbiting the star HD 65216, located approximately 114.5 light-years (35.12 parsecs) from the Solar System. First announced in 2003 by La Silla Observatory using the Radial Velocity detection technique (measuring periodic Doppler reflex motion in the host star's spectrum), this world measures 13.6 Earth radii (1.21 Jupiter radii) and has a measured mass of 411.59 Earth masses (1.3 Jupiter masses). Combining its mass and radius yields a mean bulk density of 0.9 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 2.23 g⊕ (21.87 m/s²), and an escape velocity of 61.5 km/s.
In its orbital architecture around HD 65216, HD 65216 b completes one full revolution every 577.6 Earth days (1.58Julian years) at a semi-major axis of 1.301 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 24.5 km/s (compared to Earth's 29.8 km/s). The planet follows a highly eccentric trajectory (e = 0.27, swinging from 0.9497 AU at periapsis out to 1.6523 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 65216 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 65216 is classified as a solar-type yellow star of spectral type G5 V with an effective photospheric temperature of 5,612 K, a radius of 0.88 R☉, a mass of 0.874 M☉, an estimated bolometric luminosity of 0.689 L☉. Stellar evolution modeling indicates an estimated stellar age of 4 Gyr and a metallicity of [Fe/H] = -0.169 dex (metal-poor relative to the Sun). From Earth, HD 65216 shines at apparent V-band magnitude 7.97 (accessible to binoculars and small amateur telescopes) in the Southern celestial hemisphere. The HD 65216 system is a multi-planet architecture hosting 2 confirmed worlds, with HD 65216 b sharing its stellar neighborhood alongside HD 65216 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 65216 |
| Spectral Type | G5 V |
| Effective Temp (Teff) | 5,612 K |
| Stellar Radius | 0.8800 R☉ |
| Stellar Mass | 0.8740 M☉ |
| Bolometric Luminosity | 0.689 L☉ |
| Metallicity [Fe/H] | -0.169 dex |
| Stellar Age | 4.000 Gyr |
| Apparent Magnitude | V: 7.970 · G: 7.794 |
| System Architecture | 3 Stars, 2 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 1.301000 AU |
| Orbital Period | 577.6 days |
| Mean Orbital Velocity | 24.5 km/s |
| Orbital Eccentricity (e) | 0.27000 |
| Orbital Inclination (i) | — |
| Mean Bulk Density | 0.9 g/cm³ (61.5 km/s vesc) |
| Insolation Flux | 0.4185 S⊕ (~570 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 114.500 LY (35.121 pc) |