HD 64121 b
Astrophysical Synthesis & Habitability Characterization
HD 64121 b is a confirmed gas giant exoplanet orbiting the star HD 64121, located approximately 423.9 light-years (129.97 parsecs) from the Solar System. First announced in 2022 by La Silla Observatory using the Radial Velocity detection technique (measuring periodic Doppler reflex motion in the host star's spectrum), this world measures 13.2 Earth radii (1.18 Jupiter radii) and has a measured mass of 813.641 Earth masses (2.56 Jupiter masses). Combining its mass and radius yields a mean bulk density of 1.95 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 4.67 g⊕ (45.8 m/s²), and an escape velocity of 87.8 km/s.
In its orbital architecture around HD 64121, HD 64121 b completes one full revolution every 623 Earth days (1.71Julian years) at a semi-major axis of 1.51 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 26.4 km/s (compared to Earth's 29.8 km/s). Its moderate orbital eccentricity of e = 0.11 carries the world between 1.3439 AU at periapsis and 1.6761 AU at apoapsis, driving measurable seasonal insolation cycles.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 465 K (+192°C / +378°F) and receiving 7.76 S⊕ (~10,565 W/m²), HD 64121 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star HD 64121 is classified as a solar-type yellow star of spectral type G8/K0 III with an effective photospheric temperature of 5,078 K, a radius of 5.44 R☉, a mass of 1.64 M☉, an estimated bolometric luminosity of 17.655 L☉. Stellar evolution modeling indicates a metallicity of [Fe/H] = -0.21 dex (metal-poor relative to the Sun). From Earth, HD 64121 shines at apparent V-band magnitude 7.43 (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 64121 |
| Spectral Type | G8/K0 III |
| Effective Temp (Teff) | 5,078 K |
| Stellar Radius | 5.4400 R☉ |
| Stellar Mass | 1.6400 M☉ |
| Bolometric Luminosity | 17.655 L☉ |
| Metallicity [Fe/H] | -0.210 dex |
| Stellar Age | — |
| Apparent Magnitude | V: 7.430 · G: 7.179 |
| System Architecture | 1 Star, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 1.510000 AU |
| Orbital Period | 623 days |
| Mean Orbital Velocity | 26.4 km/s |
| Orbital Eccentricity (e) | 0.11000 |
| Orbital Inclination (i) | — |
| Mean Bulk Density | 1.95 g/cm³ (87.8 km/s vesc) |
| Insolation Flux | 7.7628 S⊕ (~10,565 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 423.900 LY (129.966 pc) |