HD 28678 b
Astrophysical Synthesis & Habitability Characterization
HD 28678 b is a confirmed gas giant exoplanet orbiting the star HD 28678, located approximately 619.4 light-years (189.91 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 13.5 Earth radii (1.2 Jupiter radii) and has a measured mass of 490.094 Earth masses (1.54 Jupiter masses). Combining its mass and radius yields a mean bulk density of 1.1 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 2.69 g⊕ (26.38 m/s²), and an escape velocity of 67.4 km/s.
In its orbital architecture around HD 28678, HD 28678 b completes one full revolution every 380.2 Earth days (1.04Julian years) at a semi-major axis of 1.18 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 33.8 km/s (compared to Earth's 29.8 km/s). Its moderate orbital eccentricity of e = 0.149 carries the world between 1.0042 AU at periapsis and 1.3558 AU at apoapsis, driving measurable seasonal insolation cycles.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 562 K (+289°C / +552°F) and receiving 16.45 S⊕ (~22,384 W/m²), HD 28678 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star HD 28678 is classified as a solar-type yellow star of spectral type G8 IV with an effective photospheric temperature of 4,972 K, a radius of 6.48 R☉, a mass of 1.53 M☉, an estimated bolometric luminosity of 23.023 L☉. Stellar evolution modeling indicates an estimated stellar age of 1.8 Gyr and a metallicity of [Fe/H] = -0.11 dex (metal-poor relative to the Sun). From Earth, HD 28678 shines at apparent V-band magnitude 8.38 (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 28678 |
| Spectral Type | G8 IV |
| Effective Temp (Teff) | 4,972 K |
| Stellar Radius | 6.4800 R☉ |
| Stellar Mass | 1.5300 M☉ |
| Bolometric Luminosity | 23.023 L☉ |
| Metallicity [Fe/H] | -0.110 dex |
| Stellar Age | 1.800 Gyr |
| Apparent Magnitude | V: 8.380 · G: 8.055 |
| System Architecture | 1 Star, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 1.180000 AU |
| Orbital Period | 380.2 days |
| Mean Orbital Velocity | 33.8 km/s |
| Orbital Eccentricity (e) | 0.14900 |
| Orbital Inclination (i) | — |
| Mean Bulk Density | 1.1 g/cm³ (67.4 km/s vesc) |
| Insolation Flux | 16.4464 S⊕ (~22,384 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 619.400 LY (189.908 pc) |