HD 77338 b
Astrophysical Synthesis & Habitability Characterization
HD 77338 b is a confirmed sub-neptune exoplanet orbiting the star HD 77338, located approximately 149.8 light-years (45.94 parsecs) from the Solar System. First announced in 2012 by La Silla Observatory using the Radial Velocity detection technique (measuring periodic Doppler reflex motion in the host star's spectrum), this world measures 4.12 Earth radii (0.37 Jupiter radii) and has a measured mass of 15.9 Earth masses. Combining its mass and radius yields a mean bulk density of 1.25 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 0.94 g⊕ (9.22 m/s²), and an escape velocity of 22 km/s.
In its orbital architecture around HD 77338, HD 77338 b completes one full revolution every 5.736 Earth days at a semi-major axis of 0.06 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 113.8 km/s (compared to Earth's 29.8 km/s). Its moderate orbital eccentricity of e = 0.09 carries the world between 0.0546 AU at periapsis and 0.0654 AU at apoapsis, driving measurable seasonal insolation cycles.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 1036 K (+763°C / +1405°F) and receiving 152.79 S⊕ (~207,948 W/m²), HD 77338 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star HD 77338 is classified as an orange K-type star of spectral type K0 IV with an effective photospheric temperature of 5,341 K, a radius of 0.97 R☉, a mass of 1.37 M☉, an estimated bolometric luminosity of 0.687 L☉. Stellar evolution modeling indicates a metallicity of [Fe/H] = 0.32 dex (metal-rich relative to the Sun). From Earth, HD 77338 shines at apparent V-band magnitude 8.63 (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 77338 |
| Spectral Type | K0 IV |
| Effective Temp (Teff) | 5,341 K |
| Stellar Radius | 0.9700 R☉ |
| Stellar Mass | 1.3700 M☉ |
| Bolometric Luminosity | 0.687 L☉ |
| Metallicity [Fe/H] | 0.320 dex |
| Stellar Age | — |
| Apparent Magnitude | V: 8.630 · G: 8.410 |
| System Architecture | 1 Star, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.060000 AU |
| Orbital Period | 5.736 days |
| Mean Orbital Velocity | 113.8 km/s |
| Orbital Eccentricity (e) | 0.09000 |
| Orbital Inclination (i) | — |
| Mean Bulk Density | 1.25 g/cm³ (22 km/s vesc) |
| Insolation Flux | 152.7909 S⊕ (~207,948 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 149.800 LY (45.935 pc) |