HD 77946 b
Astrophysical Synthesis & Habitability Characterization
HD 77946 b is a confirmed sub-neptune exoplanet orbiting the star HD 77946, located approximately 324.4 light-years (99.45 parsecs) from the Solar System. First announced in 2024 by Transiting Exoplanet Survey Satellite (TESS) using the Transit detection technique (producing an estimated primary transit depth of 0.0406% across the stellar disk), this world measures 2.896 Earth radii and has a measured mass of 10.9 Earth masses. Combining its mass and radius yields a mean bulk density of 2.47 g/cm³ (an intermediate density indicative of a deep water-ice mantle or dense volatile envelope), a surface gravity of 1.3 g⊕ (12.75 m/s²), and an escape velocity of 21.7 km/s.
In its orbital architecture around HD 77946, HD 77946 b completes one full revolution every 6.527 Earth days at a semi-major axis of 0.073 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 121.7 km/s (compared to Earth's 29.8 km/s). Its moderate orbital eccentricity of e = 0.211 carries the world between 0.0576 AU at periapsis and 0.0884 AU at apoapsis, driving measurable seasonal insolation cycles.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 1129 K (+856°C / +1573°F) and receiving 413.10 S⊕ (~562,230 W/m²), HD 77946 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star HD 77946 is classified as a warm F-type star of spectral type F5 with an effective photospheric temperature of 6,007 K, a radius of 1.3174 R☉, a mass of 1.1973 M☉, an estimated bolometric luminosity of 2.027 L☉. Stellar evolution modeling indicates an estimated stellar age of 3.1 Gyr and a metallicity of [Fe/H] = 0.215 dex (metal-rich relative to the Sun). From Earth, HD 77946 shines at apparent V-band magnitude 8.99 (accessible to binoculars and small amateur telescopes) in the Northern 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: Transiting Exoplanet Survey Satellite (TESS) · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | HD 77946 |
| Spectral Type | F5 |
| Effective Temp (Teff) | 6,007 K |
| Stellar Radius | 1.3174 R☉ |
| Stellar Mass | 1.1973 M☉ |
| Bolometric Luminosity | 2.027 L☉ |
| Metallicity [Fe/H] | 0.215 dex |
| Stellar Age | 3.100 Gyr |
| Apparent Magnitude | V: 8.990 · G: 8.852 |
| System Architecture | 1 Star, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.073000 AU |
| Orbital Period | 6.527 days |
| Mean Orbital Velocity | 121.7 km/s |
| Orbital Eccentricity (e) | 0.21100 |
| Orbital Inclination (i) | 87.7900° |
| Mean Bulk Density | 2.47 g/cm³ (21.7 km/s vesc) |
| Insolation Flux | 413.1008 S⊕ (~562,230 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 324.400 LY (99.451 pc) |