NGTS-8 b
Astrophysical Synthesis & Habitability Characterization
NGTS-8 b is a confirmed gas giant exoplanet orbiting the star NGTS-8, located approximately 1399.1 light-years (428.98 parsecs) from the Solar System. First announced in 2019 by Next-Generation Transit Survey (NGTS) using the Transit detection technique (producing an estimated primary transit depth of 1.3064% across the stellar disk), this world measures 12.218 Earth radii (1.09 Jupiter radii) and has a measured mass of 295.582 Earth masses (0.93 Jupiter masses). Combining its mass and radius yields a mean bulk density of 0.89 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 1.98 g⊕ (19.42 m/s²), and an escape velocity of 55 km/s.
In its orbital architecture around NGTS-8, NGTS-8 b completes one full revolution every 2.5 Earth days at a semi-major axis of 0.035 AU (an ultra-close orbit less than one-seventh of Mercury's 0.387 AU distance from the Sun, where strong stellar tidal forces typically induce synchronous rotation). Its mean orbital velocity is approximately 152.3 km/s (compared to Earth's 29.8 km/s). With a near-circular eccentricity of e = 0.01 (ranging from 0.0347 AU at periapsis to 0.0354 AU at apoapsis), the planet experiences minimal orbital distance variation.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 1345 K (+1072°C / +1962°F) and receiving 503.00 S⊕ (~684,583 W/m²), NGTS-8 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star NGTS-8 is classified as an orange K-type star of spectral type K0 V with an effective photospheric temperature of 5,241 K, a radius of 0.98 R☉, a mass of 0.89 M☉, an estimated bolometric luminosity of 0.65 L☉. Stellar evolution modeling indicates an estimated stellar age of 12.48 Gyr and a metallicity of [Fe/H] = 0.24 dex (metal-rich relative to the Sun). From Earth, NGTS-8 shines at apparent V-band magnitude 13.69 (faint and requiring research-grade or CCD telescopic photometry) in the Southern 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: Next-Generation Transit Survey (NGTS) · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | NGTS-8 |
| Spectral Type | K0 V |
| Effective Temp (Teff) | 5,241 K |
| Stellar Radius | 0.9800 R☉ |
| Stellar Mass | 0.8900 M☉ |
| Bolometric Luminosity | 0.65 L☉ |
| Metallicity [Fe/H] | 0.240 dex |
| Stellar Age | 12.480 Gyr |
| Apparent Magnitude | V: 13.690 · G: 13.495 |
| System Architecture | 1 Star, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.035000 AU |
| Orbital Period | 2.5 days |
| Mean Orbital Velocity | 152.3 km/s |
| Orbital Eccentricity (e) | 0.01000 |
| Orbital Inclination (i) | 86.9000° |
| Mean Bulk Density | 0.89 g/cm³ (55 km/s vesc) |
| Insolation Flux | 503.0000 S⊕ (~684,583 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 1399.100 LY (428.976 pc) |