HD 99706 c
Astrophysical Synthesis & Habitability Characterization
HD 99706 c is a confirmed gas giant exoplanet orbiting the star HD 99706, located approximately 478.1 light-years (146.6 parsecs) from the Solar System. First announced in 2016 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 12.8 Earth radii (1.14 Jupiter radii) and has a measured mass of 1808.453 Earth masses (5.69 Jupiter masses). Combining its mass and radius yields a mean bulk density of 4.75 g/cm³ (a terrestrial silicate-iron composition comparable to Earth (5.51 g/cm³)), a surface gravity of 11.04 g⊕ (108.27 m/s²), and an escape velocity of 133 km/s.
In its orbital architecture around HD 99706, HD 99706 c completes one full revolution every 1278 Earth days (3.5Julian years). The planet follows a highly eccentric trajectory (e = 0.411), pointing to past dynamical scattering or secular gravitational perturbations.
☁️ Atmospheric Regime (Volatile / Gas Envelope): With a radius of 12.800 R⊕, HD 99706 c 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 99706 is classified as an orange K-type star of spectral type K0 with an effective photospheric temperature of 4,891 K, a radius of 5.4 R☉, a mass of 1.72 M☉, an estimated bolometric luminosity of 14.972 L☉. Stellar evolution modeling indicates an estimated stellar age of 2.1 Gyr and a metallicity of [Fe/H] = 0.14 dex (metal-rich relative to the Sun). From Earth, HD 99706 shines at apparent V-band magnitude 7.65 (accessible to binoculars and small amateur telescopes) in the Northern celestial hemisphere. The HD 99706 system is a multi-planet architecture hosting 2 confirmed worlds, with HD 99706 c sharing its stellar neighborhood alongside HD 99706 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 99706 |
| Spectral Type | K0 |
| Effective Temp (Teff) | 4,891 K |
| Stellar Radius | 5.4000 R☉ |
| Stellar Mass | 1.7200 M☉ |
| Bolometric Luminosity | 14.972 L☉ |
| Metallicity [Fe/H] | 0.140 dex |
| Stellar Age | 2.100 Gyr |
| Apparent Magnitude | V: 7.650 · G: 7.377 |
| System Architecture | 1 Star, 2 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | — |
| Orbital Period | 1278 days |
| Orbital Eccentricity (e) | 0.41100 |
| Orbital Inclination (i) | — |
| Mean Bulk Density | 4.75 g/cm³ (133 km/s vesc) |
| Insolation Flux | — |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 478.100 LY (146.600 pc) |