HD 160691 d
Astrophysical Synthesis & Habitability Characterization
HD 160691 d is a confirmed sub-neptune exoplanet orbiting the star HD 160691, located approximately 50.9 light-years (15.6 parsecs) from the Solar System. First announced in 2004 by La Silla Observatory using the Radial Velocity detection technique (measuring periodic Doppler reflex motion in the host star's spectrum), this world measures 3.23 Earth radii (0.29 Jupiter radii) and has a measured mass of 10.49 Earth masses. Combining its mass and radius yields a mean bulk density of 1.72 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 1.01 g⊕ (9.9 m/s²), and an escape velocity of 20.2 km/s.
In its orbital architecture around HD 160691, HD 160691 d completes one full revolution every 9.639 Earth days at a semi-major axis of 0.0952 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 107.4 km/s (compared to Earth's 29.8 km/s). The orbit is modeled as circular (e = 0.00), maintaining a constant stellar distance throughout its year.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 900 K (+627°C / +1161°F) and receiving 209.51 S⊕ (~285,144 W/m²), HD 160691 d orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star HD 160691 is classified as a solar-type yellow star of spectral type G3 IV-V with an effective photospheric temperature of 5,773 K, a radius of 1.33 R☉, a mass of 1.13 M☉, an estimated bolometric luminosity of 1.763 L☉. Stellar evolution modeling indicates an estimated stellar age of 5.7 Gyr and a metallicity of [Fe/H] = 0.28 dex (metal-rich relative to the Sun). From Earth, HD 160691 shines at apparent V-band magnitude 5.12 (visible to the unaided human eye under dark skies) in the Southern celestial hemisphere. The HD 160691 system is a multi-planet architecture hosting 4 confirmed worlds, with HD 160691 d sharing its stellar neighborhood alongside HD 160691 e, HD 160691 b, HD 160691 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 160691 |
| Spectral Type | G3 IV-V |
| Effective Temp (Teff) | 5,773 K |
| Stellar Radius | 1.3300 R☉ |
| Stellar Mass | 1.1300 M☉ |
| Bolometric Luminosity | 1.763 L☉ |
| Metallicity [Fe/H] | 0.280 dex |
| Stellar Age | 5.700 Gyr |
| Apparent Magnitude | V: 5.120 · G: 4.949 |
| System Architecture | 1 Star, 4 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.095200 AU |
| Orbital Period | 9.639 days |
| Mean Orbital Velocity | 107.4 km/s |
| Orbital Eccentricity (e) | 0.00000 |
| Orbital Inclination (i) | — |
| Mean Bulk Density | 1.72 g/cm³ (20.2 km/s vesc) |
| Insolation Flux | 209.5104 S⊕ (~285,144 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 50.900 LY (15.598 pc) |