HD 109271 b
Astrophysical Synthesis & Habitability Characterization
HD 109271 b is a confirmed sub-neptune exoplanet orbiting the star HD 109271, located approximately 182.2 light-years (55.87 parsecs) from the Solar System. First announced in 2013 by La Silla Observatory using the Radial Velocity detection technique (measuring periodic Doppler reflex motion in the host star's spectrum), this world measures 4.31 Earth radii (0.38 Jupiter radii) and has a measured mass of 17.162 Earth masses. Combining its mass and radius yields a mean bulk density of 1.18 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 0.92 g⊕ (9.02 m/s²), and an escape velocity of 22.3 km/s.
In its orbital architecture around HD 109271, HD 109271 b completes one full revolution every 7.854 Earth days at a semi-major axis of 0.079 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 109.4 km/s (compared to Earth's 29.8 km/s). The planet follows a highly eccentric trajectory (e = 0.25, swinging from 0.0593 AU at periapsis out to 0.0988 AU at apoapsis), pointing to past dynamical scattering or secular gravitational perturbations.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 1129 K (+856°C / +1573°F) and receiving 320.44 S⊕ (~436,118 W/m²), HD 109271 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star HD 109271 is classified as a solar-type yellow star of spectral type G5 V with an effective photospheric temperature of 5,783 K, a radius of 1.2946 R☉, a mass of 1.047 M☉, an estimated bolometric luminosity of 1.682 L☉. Stellar evolution modeling indicates an estimated stellar age of 7.3 Gyr and a metallicity of [Fe/H] = 0.1 dex (metal-rich relative to the Sun). From Earth, HD 109271 shines at apparent V-band magnitude 8.04 (accessible to binoculars and small amateur telescopes) in the Southern celestial hemisphere. The HD 109271 system is a multi-planet architecture hosting 2 confirmed worlds, with HD 109271 b sharing its stellar neighborhood alongside HD 109271 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: La Silla Observatory · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | HD 109271 |
| Spectral Type | G5 V |
| Effective Temp (Teff) | 5,783 K |
| Stellar Radius | 1.2946 R☉ |
| Stellar Mass | 1.0470 M☉ |
| Bolometric Luminosity | 1.682 L☉ |
| Metallicity [Fe/H] | 0.100 dex |
| Stellar Age | 7.300 Gyr |
| Apparent Magnitude | V: 8.040 · G: 7.878 |
| System Architecture | 1 Star, 2 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.079000 AU |
| Orbital Period | 7.854 days |
| Mean Orbital Velocity | 109.4 km/s |
| Orbital Eccentricity (e) | 0.25000 |
| Orbital Inclination (i) | — |
| Mean Bulk Density | 1.18 g/cm³ (22.3 km/s vesc) |
| Insolation Flux | 320.4393 S⊕ (~436,118 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 182.200 LY (55.872 pc) |