HR 8799 d
Astrophysical Synthesis & Habitability Characterization
HR 8799 d is a confirmed gas giant exoplanet orbiting the star HR 8799, located approximately 134.5 light-years (41.24 parsecs) from the Solar System. First announced in 2008 by W. M. Keck Observatory using the Imaging detection technique (resolved directly via high-contrast coronagraphic or interferometric imaging), this world measures 13 Earth radii (1.16 Jupiter radii) and has a measured mass of 3000 Earth masses (9.44 Jupiter masses). Combining its mass and radius yields a mean bulk density of 7.53 g/cm³ (an iron-enriched, high-compression rocky core), a surface gravity of 17.75 g⊕ (174.07 m/s²), and an escape velocity of 169.9 km/s.
In its orbital architecture around HR 8799, HR 8799 d completes one full revolution every 37000 Earth days (101.3Julian years) at a semi-major axis of 24 AU (a wide outer-system orbit beyond Jupiter's 5.20 AU distance in our Solar System). Its mean orbital velocity is approximately 7.1 km/s (compared to Earth's 29.8 km/s). The planet follows a highly eccentric trajectory (e = 0.6, swinging from 9.6 AU at periapsis out to 38.4 AU at apoapsis), pointing to past dynamical scattering or secular gravitational perturbations.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 1300 K (+1027°C / +1881°F) and receiving 0.01 S⊕ (~12 W/m²), HR 8799 d orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star HR 8799 is classified as a luminous A-type star of spectral type A5 V with an effective photospheric temperature of 7,205 K, a radius of 1.4934 R☉, a mass of 1.5 M☉, an estimated bolometric luminosity of 5.392 L☉. Stellar evolution modeling indicates an estimated stellar age of 0.06 Gyr and a metallicity of [Fe/H] = -0.47 dex (metal-poor relative to the Sun). From Earth, HR 8799 shines at apparent V-band magnitude 5.98 (visible to the unaided human eye under dark skies) in the Northern celestial hemisphere. The HR 8799 system is a multi-planet architecture hosting 4 confirmed worlds, with HR 8799 d sharing its stellar neighborhood alongside HR 8799 e, HR 8799 c, HR 8799 b.
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 | HR 8799 |
| Spectral Type | A5 V |
| Effective Temp (Teff) | 7,205 K |
| Stellar Radius | 1.4934 R☉ |
| Stellar Mass | 1.5000 M☉ |
| Bolometric Luminosity | 5.392 L☉ |
| Metallicity [Fe/H] | -0.470 dex |
| Stellar Age | 0.060 Gyr |
| Apparent Magnitude | V: 5.980 · G: 5.909 |
| System Architecture | 1 Star, 4 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 24.000000 AU |
| Orbital Period | 37000 days |
| Mean Orbital Velocity | 7.1 km/s |
| Orbital Eccentricity (e) | 0.60000 |
| Orbital Inclination (i) | 38.6300° |
| Mean Bulk Density | 7.53 g/cm³ (169.9 km/s vesc) |
| Insolation Flux | 0.0085 S⊕ (~12 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 134.500 LY (41.244 pc) |