HD 210702 b
Astrophysical Synthesis & Habitability Characterization
HD 210702 b is a confirmed gas giant exoplanet orbiting the star HD 210702, located approximately 176.8 light-years (54.2 parsecs) from the Solar System. First announced in 2007 by Lick 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 481.51 Earth masses (1.51 Jupiter masses). Combining its mass and radius yields a mean bulk density of 1.06 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 2.6 g⊕ (25.5 m/s²), and an escape velocity of 66.6 km/s.
In its orbital architecture around HD 210702, HD 210702 b completes one full revolution every 355.5 Earth days at a semi-major axis of 1.079 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 km/s (compared to Earth's 29.8 km/s). Its moderate orbital eccentricity of e = 0.071 carries the world between 1.0024 AU at periapsis and 1.1556 AU at apoapsis, driving measurable seasonal insolation cycles.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 486 K (+213°C / +415°F) and receiving 9.32 S⊕ (~12,684 W/m²), HD 210702 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star HD 210702 is classified as an orange K-type star of spectral type K1 IV with an effective photospheric temperature of 4,912 K, a radius of 4.54 R☉, a mass of 1.33 M☉, an estimated bolometric luminosity of 10.766 L☉. Stellar evolution modeling indicates an estimated stellar age of 2.1 Gyr and a metallicity of [Fe/H] = -0.02 dex (near-solar heavy-element abundance). From Earth, HD 210702 shines at apparent V-band magnitude 5.93 (visible to the unaided human eye under dark skies) 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: Lick Observatory · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | HD 210702 |
| Spectral Type | K1 IV |
| Effective Temp (Teff) | 4,912 K |
| Stellar Radius | 4.5400 R☉ |
| Stellar Mass | 1.3300 M☉ |
| Bolometric Luminosity | 10.766 L☉ |
| Metallicity [Fe/H] | -0.020 dex |
| Stellar Age | 2.100 Gyr |
| Apparent Magnitude | V: 5.930 · G: 5.681 |
| System Architecture | 1 Star, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 1.079000 AU |
| Orbital Period | 355.5 days |
| Mean Orbital Velocity | 33 km/s |
| Orbital Eccentricity (e) | 0.07100 |
| Orbital Inclination (i) | — |
| Mean Bulk Density | 1.06 g/cm³ (66.6 km/s vesc) |
| Insolation Flux | 9.3194 S⊕ (~12,684 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 176.800 LY (54.196 pc) |