HD 11964 c
Astrophysical Synthesis & Habitability Characterization
HD 11964 c is a confirmed sub-neptune exoplanet orbiting the star HD 11964, located approximately 109.4 light-years (33.54 parsecs) from the Solar System. First announced in 2008 by W. M. Keck Observatory using the Radial Velocity detection technique (measuring periodic Doppler reflex motion in the host star's spectrum), this world measures 5.38 Earth radii (0.48 Jupiter radii) and has a measured mass of 25 Earth masses. Combining its mass and radius yields a mean bulk density of 0.89 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 0.86 g⊕ (8.43 m/s²), and an escape velocity of 24.1 km/s.
In its orbital architecture around HD 11964, HD 11964 c completes one full revolution every 37.91 Earth days at a semi-major axis of 0.229 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 65.7 km/s (compared to Earth's 29.8 km/s). The planet follows a highly eccentric trajectory (e = 0.3, swinging from 0.1603 AU at periapsis out to 0.2977 AU at apoapsis), pointing to past dynamical scattering or secular gravitational perturbations.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 758 K (+485°C / +905°F) and receiving 54.88 S⊕ (~74,685 W/m²), HD 11964 c orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star HD 11964 is classified as a solar-type yellow star of spectral type G9 V CN+1 with an effective photospheric temperature of 5,303 K, a radius of 2.0097 R☉, a mass of 0.91 M☉, an estimated bolometric luminosity of 2.866 L☉. Stellar evolution modeling indicates an estimated stellar age of 7.45 Gyr and a metallicity of [Fe/H] = 0.1 dex (metal-rich relative to the Sun). From Earth, HD 11964 shines at apparent V-band magnitude 6.415 (accessible to binoculars and small amateur telescopes) in the Southern celestial hemisphere. The HD 11964 system is a multi-planet architecture hosting 2 confirmed worlds, with HD 11964 c sharing its stellar neighborhood alongside HD 11964 b.
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: W. M. Keck Observatory · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | HD 11964 |
| Spectral Type | G9 V CN+1 |
| Effective Temp (Teff) | 5,303 K |
| Stellar Radius | 2.0097 R☉ |
| Stellar Mass | 0.9100 M☉ |
| Bolometric Luminosity | 2.866 L☉ |
| Metallicity [Fe/H] | 0.100 dex |
| Stellar Age | 7.450 Gyr |
| Apparent Magnitude | V: 6.415 · G: 6.209 |
| System Architecture | 2 Stars, 2 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.229000 AU |
| Orbital Period | 37.91 days |
| Mean Orbital Velocity | 65.7 km/s |
| Orbital Eccentricity (e) | 0.30000 |
| Orbital Inclination (i) | — |
| Mean Bulk Density | 0.89 g/cm³ (24.1 km/s vesc) |
| Insolation Flux | 54.8750 S⊕ (~74,685 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 109.400 LY (33.537 pc) |