NGTS-15 b
Astrophysical Synthesis & Habitability Characterization
NGTS-15 b is a confirmed gas giant exoplanet orbiting the star NGTS-15, located approximately 2565.2 light-years (786.49 parsecs) from the Solar System. First announced in 2021 by Next-Generation Transit Survey (NGTS) using the Transit detection technique (producing an estimated primary transit depth of 1.404% across the stellar disk), this world measures 12.33 Earth radii (1.1 Jupiter radii) and has a measured mass of 238.689 Earth masses (0.75 Jupiter masses). Combining its mass and radius yields a mean bulk density of 0.7 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 1.57 g⊕ (15.4 m/s²), and an escape velocity of 49.2 km/s.
In its orbital architecture around NGTS-15, NGTS-15 b completes one full revolution every 3.276 Earth days at a semi-major axis of 0.0441 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 146.4 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 1146 K (+873°C / +1603°F) and receiving 425.00 S⊕ (~578,425 W/m²), NGTS-15 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star NGTS-15 is classified as a solar-type yellow star of spectral type G6 V with an effective photospheric temperature of 5,600 K, a radius of 0.954 R☉, a mass of 0.995 M☉, an estimated bolometric luminosity of 0.803 L☉. Stellar evolution modeling indicates an estimated stellar age of 3.28 Gyr and a metallicity of [Fe/H] = 0.15 dex (metal-rich relative to the Sun). From Earth, NGTS-15 shines at apparent V-band magnitude 14.669 (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-15 |
| Spectral Type | G6 V |
| Effective Temp (Teff) | 5,600 K |
| Stellar Radius | 0.9540 R☉ |
| Stellar Mass | 0.9950 M☉ |
| Bolometric Luminosity | 0.803 L☉ |
| Metallicity [Fe/H] | 0.150 dex |
| Stellar Age | 3.280 Gyr |
| Apparent Magnitude | V: 14.669 · G: 14.430 |
| System Architecture | 1 Star, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.044100 AU |
| Orbital Period | 3.276 days |
| Mean Orbital Velocity | 146.4 km/s |
| Orbital Eccentricity (e) | 0.00000 |
| Orbital Inclination (i) | — |
| Mean Bulk Density | 0.7 g/cm³ (49.2 km/s vesc) |
| Insolation Flux | 425.0000 S⊕ (~578,425 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 2565.200 LY (786.485 pc) |