HD 85390 b
Astrophysical Synthesis & Habitability Characterization
HD 85390 b is a confirmed gas giant exoplanet orbiting the star HD 85390, located approximately 109.3 light-years (33.52 parsecs) from the Solar System. First announced in 2011 by La Silla Observatory using the Radial Velocity detection technique (measuring periodic Doppler reflex motion in the host star's spectrum), this world measures 6.16 Earth radii (0.55 Jupiter radii) and has a measured mass of 31.465 Earth masses (0.1 Jupiter masses). Combining its mass and radius yields a mean bulk density of 0.74 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 0.83 g⊕ (8.14 m/s²), and an escape velocity of 25.3 km/s.
In its orbital architecture around HD 85390, HD 85390 b completes one full revolution every 799.52 Earth days (2.19Julian years) at a semi-major axis of 1.373 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 18.7 km/s (compared to Earth's 29.8 km/s). The planet follows a highly eccentric trajectory (e = 0.5, swinging from 0.6865 AU at periapsis out to 2.0595 AU at apoapsis), pointing to past dynamical scattering or secular gravitational perturbations.
☁️ Atmospheric Regime (Volatile / Gas Envelope): With a radius of 6.160 R⊕, HD 85390 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 85390 is classified as an orange K-type star of spectral type K1.5 V with an effective photospheric temperature of 5,186 K, a radius of 0.8 R☉, a mass of 0.758 M☉, an estimated bolometric luminosity of 0.415 L☉. Stellar evolution modeling indicates an estimated stellar age of 7.2 Gyr and a metallicity of [Fe/H] = -0.07 dex (near-solar heavy-element abundance). From Earth, HD 85390 shines at apparent V-band magnitude 8.54 (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: La Silla Observatory · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | HD 85390 |
| Spectral Type | K1.5 V |
| Effective Temp (Teff) | 5,186 K |
| Stellar Radius | 0.8000 R☉ |
| Stellar Mass | 0.7580 M☉ |
| Bolometric Luminosity | 0.415 L☉ |
| Metallicity [Fe/H] | -0.070 dex |
| Stellar Age | 7.200 Gyr |
| Apparent Magnitude | V: 8.540 · G: 8.295 |
| System Architecture | 1 Star, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 1.373000 AU |
| Orbital Period | 799.52 days |
| Mean Orbital Velocity | 18.7 km/s |
| Orbital Eccentricity (e) | 0.50000 |
| Orbital Inclination (i) | — |
| Mean Bulk Density | 0.74 g/cm³ (25.3 km/s vesc) |
| Insolation Flux | 0.2281 S⊕ (~310 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 109.300 LY (33.523 pc) |