HD 75898 b
Astrophysical Synthesis & Habitability Characterization
HD 75898 b is a confirmed gas giant exoplanet orbiting the star HD 75898, located approximately 254.6 light-years (78.05 parsecs) from the Solar System. First announced in 2007 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 13.2 Earth radii (1.18 Jupiter radii) and has a measured mass of 810.462 Earth masses (2.55 Jupiter masses). Combining its mass and radius yields a mean bulk density of 1.94 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 4.65 g⊕ (45.6 m/s²), and an escape velocity of 87.7 km/s.
In its orbital architecture around HD 75898, HD 75898 b completes one full revolution every 422.82 Earth days (1.16Julian years) at a semi-major axis of 1.2025 AU (comparable to the inner terrestrial zone between Venus, Earth at 1.00 AU, and Mars at 1.52 AU). Its mean orbital velocity is approximately 30.9 km/s (compared to Earth's 29.8 km/s). Its moderate orbital eccentricity of e = 0.105 carries the world between 1.0762 AU at periapsis and 1.3288 AU at apoapsis, driving measurable seasonal insolation cycles.
☁️ Atmospheric Regime (Volatile / Gas Envelope): With a radius of 13.200 R⊕, HD 75898 b 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 75898 is classified as a warm F-type star of spectral type F8 V with an effective photospheric temperature of 6,122 K, a radius of 1.55 R☉, a mass of 1.295 M☉, an estimated bolometric luminosity of 3.028 L☉. Stellar evolution modeling indicates an estimated stellar age of 3.2 Gyr and a metallicity of [Fe/H] = 0.29 dex (metal-rich relative to the Sun). From Earth, HD 75898 shines at apparent V-band magnitude 8.03 (accessible to binoculars and small amateur telescopes) in the Northern celestial hemisphere. The HD 75898 system is a multi-planet architecture hosting 2 confirmed worlds, with HD 75898 b sharing its stellar neighborhood alongside HD 75898 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 75898 |
| Spectral Type | F8 V |
| Effective Temp (Teff) | 6,122 K |
| Stellar Radius | 1.5500 R☉ |
| Stellar Mass | 1.2950 M☉ |
| Bolometric Luminosity | 3.028 L☉ |
| Metallicity [Fe/H] | 0.290 dex |
| Stellar Age | 3.200 Gyr |
| Apparent Magnitude | V: 8.030 · G: 7.896 |
| System Architecture | 1 Star, 2 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 1.202500 AU |
| Orbital Period | 422.82 days |
| Mean Orbital Velocity | 30.9 km/s |
| Orbital Eccentricity (e) | 0.10500 |
| Orbital Inclination (i) | — |
| Mean Bulk Density | 1.94 g/cm³ (87.7 km/s vesc) |
| Insolation Flux | 1.9945 S⊕ (~2,715 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 254.600 LY (78.051 pc) |