HD 210277 b
Astrophysical Synthesis & Habitability Characterization
HD 210277 b is a confirmed gas giant exoplanet orbiting the star HD 210277, located approximately 69.5 light-years (21.3 parsecs) from the Solar System. First announced in 1998 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 13.6 Earth radii (1.21 Jupiter radii) and has a measured mass of 410.001 Earth masses (1.29 Jupiter masses). Combining its mass and radius yields a mean bulk density of 0.9 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 2.22 g⊕ (21.77 m/s²), and an escape velocity of 61.4 km/s.
In its orbital architecture around HD 210277, HD 210277 b completes one full revolution every 442.19 Earth days (1.21Julian years) at a semi-major axis of 1.13 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 27.8 km/s (compared to Earth's 29.8 km/s). The planet follows a highly eccentric trajectory (e = 0.48, swinging from 0.5876 AU at periapsis out to 1.6724 AU at apoapsis), pointing to past dynamical scattering or secular gravitational perturbations.
☁️ Atmospheric Regime (Volatile / Gas Envelope): With a radius of 13.600 R⊕, HD 210277 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 210277 is classified as a solar-type yellow star of spectral type G0 V with an effective photospheric temperature of 5,538 K, a radius of 1.07 R☉, a mass of 1.01 M☉, an estimated bolometric luminosity of 0.966 L☉. Stellar evolution modeling indicates an estimated stellar age of 12 Gyr and a metallicity of [Fe/H] = 0.22 dex (metal-rich relative to the Sun). From Earth, HD 210277 shines at apparent V-band magnitude 6.543 (accessible to binoculars and small amateur telescopes) in the Southern 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 210277 |
| Spectral Type | G0 V |
| Effective Temp (Teff) | 5,538 K |
| Stellar Radius | 1.0700 R☉ |
| Stellar Mass | 1.0100 M☉ |
| Bolometric Luminosity | 0.966 L☉ |
| Metallicity [Fe/H] | 0.220 dex |
| Stellar Age | 12.000 Gyr |
| Apparent Magnitude | V: 6.543 · G: 6.347 |
| System Architecture | 1 Star, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 1.130000 AU |
| Orbital Period | 442.19 days |
| Mean Orbital Velocity | 27.8 km/s |
| Orbital Eccentricity (e) | 0.48000 |
| Orbital Inclination (i) | — |
| Mean Bulk Density | 0.9 g/cm³ (61.4 km/s vesc) |
| Insolation Flux | 0.7275 S⊕ (~990 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 69.500 LY (21.299 pc) |