HD 97658 b
Astrophysical Synthesis & Habitability Characterization
HD 97658 b is a confirmed sub-neptune exoplanet orbiting the star HD 97658, located approximately 70.3 light-years (21.56 parsecs) from the Solar System. First announced in 2010 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 2.12 Earth radii and has a measured mass of 8.3 Earth masses. Combining its mass and radius yields a mean bulk density of 4.8 g/cm³ (a terrestrial silicate-iron composition comparable to Earth (5.51 g/cm³)), a surface gravity of 1.85 g⊕ (18.14 m/s²), and an escape velocity of 22.1 km/s.
In its orbital architecture around HD 97658, HD 97658 b completes one full revolution every 9.49 Earth days at a semi-major axis of 0.0805 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 92.3 km/s (compared to Earth's 29.8 km/s). Its moderate orbital eccentricity of e = 0.05 carries the world between 0.0765 AU at periapsis and 0.0845 AU at apoapsis, driving measurable seasonal insolation cycles.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 751 K (+478°C / +892°F) and receiving 41.92 S⊕ (~57,059 W/m²), HD 97658 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star HD 97658 is classified as an orange K-type star of spectral type K1 V with an effective photospheric temperature of 5,212 K, a radius of 0.728 R☉, a mass of 0.85 M☉, an estimated bolometric luminosity of 0.351 L☉. Stellar evolution modeling indicates an estimated stellar age of 3.9 Gyr and a metallicity of [Fe/H] = -0.23 dex (metal-poor relative to the Sun). From Earth, HD 97658 shines at apparent V-band magnitude 7.76 (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: W. M. Keck Observatory · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | HD 97658 |
| Spectral Type | K1 V |
| Effective Temp (Teff) | 5,212 K |
| Stellar Radius | 0.7280 R☉ |
| Stellar Mass | 0.8500 M☉ |
| Bolometric Luminosity | 0.351 L☉ |
| Metallicity [Fe/H] | -0.230 dex |
| Stellar Age | 3.900 Gyr |
| Apparent Magnitude | V: 7.760 · G: 7.514 |
| System Architecture | 1 Star, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.080500 AU |
| Orbital Period | 9.49 days |
| Mean Orbital Velocity | 92.3 km/s |
| Orbital Eccentricity (e) | 0.05000 |
| Orbital Inclination (i) | 89.0500° |
| Mean Bulk Density | 4.8 g/cm³ (22.1 km/s vesc) |
| Insolation Flux | 41.9240 S⊕ (~57,059 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 70.300 LY (21.562 pc) |