HD 99492 b
Astrophysical Synthesis & Habitability Characterization
HD 99492 b is a confirmed sub-neptune exoplanet orbiting the star HD 99492, located approximately 59.4 light-years (18.2 parsecs) from the Solar System. First announced in 2004 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 5.44 Earth radii (0.49 Jupiter radii) and has a measured mass of 25.5 Earth masses. Combining its mass and radius yields a mean bulk density of 0.87 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 24.2 km/s.
In its orbital architecture around HD 99492, HD 99492 b completes one full revolution every 17.05 Earth days at a semi-major axis of 0.12 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 76.6 km/s (compared to Earth's 29.8 km/s). With a near-circular eccentricity of e = 0.034 (ranging from 0.1159 AU at periapsis to 0.1241 AU at apoapsis), the planet experiences minimal orbital distance variation.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 622 K (+349°C / +660°F) and receiving 23.27 S⊕ (~31,667 W/m²), HD 99492 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star HD 99492 is classified as an orange K-type star of spectral type K2 V with an effective photospheric temperature of 4,929 K, a radius of 0.8225 R☉, a mass of 0.85 M☉, an estimated bolometric luminosity of 0.358 L☉. Stellar evolution modeling indicates an estimated stellar age of 4.8 Gyr and a metallicity of [Fe/H] = 0.3 dex (metal-rich relative to the Sun). From Earth, HD 99492 shines at apparent V-band magnitude 7.567 (accessible to binoculars and small amateur telescopes) in the Northern celestial hemisphere. The HD 99492 system is a multi-planet architecture hosting 2 confirmed worlds, with HD 99492 b sharing its stellar neighborhood alongside HD 99492 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 99492 |
| Spectral Type | K2 V |
| Effective Temp (Teff) | 4,929 K |
| Stellar Radius | 0.8225 R☉ |
| Stellar Mass | 0.8500 M☉ |
| Bolometric Luminosity | 0.358 L☉ |
| Metallicity [Fe/H] | 0.300 dex |
| Stellar Age | 4.800 Gyr |
| Apparent Magnitude | V: 7.567 · G: 7.260 |
| System Architecture | 2 Stars, 2 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.120000 AU |
| Orbital Period | 17.05 days |
| Mean Orbital Velocity | 76.6 km/s |
| Orbital Eccentricity (e) | 0.03400 |
| Orbital Inclination (i) | — |
| Mean Bulk Density | 0.87 g/cm³ (24.2 km/s vesc) |
| Insolation Flux | 23.2671 S⊕ (~31,667 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 59.400 LY (18.204 pc) |