HD 176986 d
Astrophysical Synthesis & Habitability Characterization
HD 176986 d is a confirmed sub-neptune exoplanet orbiting the star HD 176986, located approximately 90.6 light-years (27.78 parsecs) from the Solar System. First announced in 2026 by Multiple Observatories using the Radial Velocity detection technique (measuring periodic Doppler reflex motion in the host star's spectrum), this world measures 2.49 Earth radii and has a measured mass of 6.76 Earth masses. Combining its mass and radius yields a mean bulk density of 2.41 g/cm³ (an intermediate density indicative of a deep water-ice mantle or dense volatile envelope), a surface gravity of 1.09 g⊕ (10.69 m/s²), and an escape velocity of 18.4 km/s.
In its orbital architecture around HD 176986, HD 176986 d completes one full revolution every 61.376 Earth days at a semi-major axis of 0.28149 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 49.9 km/s (compared to Earth's 29.8 km/s).
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 363 K (+90°C / +194°F) and receiving 4.09 S⊕ (~5,566 W/m²), HD 176986 d orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star HD 176986 is classified as an orange K-type star of spectral type K2.5 V with an effective photospheric temperature of 4,931 K, a radius of 0.782 R☉, a mass of 0.789 M☉, an estimated bolometric luminosity of 0.324 L☉. Stellar evolution modeling indicates an estimated stellar age of 4.3 Gyr and a metallicity of [Fe/H] = 0.03 dex (near-solar heavy-element abundance). From Earth, HD 176986 shines at apparent V-band magnitude 8.42 (accessible to binoculars and small amateur telescopes) in the Southern celestial hemisphere. The HD 176986 system is a multi-planet architecture hosting 3 confirmed worlds, with HD 176986 d sharing its stellar neighborhood alongside HD 176986 b, HD 176986 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: Multiple Observatories · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | HD 176986 |
| Spectral Type | K2.5 V |
| Effective Temp (Teff) | 4,931 K |
| Stellar Radius | 0.7820 R☉ |
| Stellar Mass | 0.7890 M☉ |
| Bolometric Luminosity | 0.324 L☉ |
| Metallicity [Fe/H] | 0.030 dex |
| Stellar Age | 4.300 Gyr |
| Apparent Magnitude | V: 8.420 · G: 8.142 |
| System Architecture | 1 Star, 3 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.281490 AU |
| Orbital Period | 61.376 days |
| Mean Orbital Velocity | 49.9 km/s |
| Orbital Eccentricity (e) | Circular (0.00) |
| Orbital Inclination (i) | — |
| Mean Bulk Density | 2.41 g/cm³ (18.4 km/s vesc) |
| Insolation Flux | 4.0900 S⊕ (~5,566 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 90.600 LY (27.784 pc) |