HD 99706 b
Astrophysical Synthesis & Habitability Characterization
HD 99706 b 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 2011 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 13.7 Earth radii (1.22 Jupiter radii) and has a measured mass of 390.931 Earth masses (1.23 Jupiter masses). Combining its mass and radius yields a mean bulk density of 0.84 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 2.08 g⊕ (20.4 m/s²), and an escape velocity of 59.8 km/s.
In its orbital architecture around HD 99706, HD 99706 b completes one full revolution every 841 Earth days (2.3Julian years) at a semi-major axis of 1.98 AU (corresponding to the middle-system regime between Mars at 1.52 AU and Jupiter at 5.20 AU). Its mean orbital velocity is approximately 25.6 km/s (compared to Earth's 29.8 km/s). The planet follows a highly eccentric trajectory (e = 0.25, swinging from 1.485 AU at periapsis out to 2.475 AU at apoapsis), pointing to past dynamical scattering or secular gravitational perturbations.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 391 K (+118°C / +244°F) and receiving 3.93 S⊕ (~5,346 W/m²), HD 99706 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star HD 99706 is classified as an orange K-type star of spectral type K0 with an effective photospheric temperature of 4,862 K, a radius of 5.52 R☉, a mass of 1.46 M☉, an estimated bolometric luminosity of 15.277 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 b sharing its stellar neighborhood alongside HD 99706 c.
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) | 4,862 K |
| Stellar Radius | 5.5200 R☉ |
| Stellar Mass | 1.4600 M☉ |
| Bolometric Luminosity | 15.277 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) | 1.980000 AU |
| Orbital Period | 841 days |
| Mean Orbital Velocity | 25.6 km/s |
| Orbital Eccentricity (e) | 0.25000 |
| Orbital Inclination (i) | — |
| Mean Bulk Density | 0.84 g/cm³ (59.8 km/s vesc) |
| Insolation Flux | 3.9282 S⊕ (~5,346 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 478.100 LY (146.600 pc) |