NGTS-4 b
Astrophysical Synthesis & Habitability Characterization
NGTS-4 b is a confirmed sub-neptune exoplanet orbiting the star NGTS-4, located approximately 915 light-years (280.56 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 0.1205% across the stellar disk), this world measures 3.18 Earth radii (0.28 Jupiter radii) and has a measured mass of 20.6 Earth masses. Combining its mass and radius yields a mean bulk density of 3.53 g/cm³ (an intermediate density indicative of a deep water-ice mantle or dense volatile envelope), a surface gravity of 2.04 g⊕ (20.01 m/s²), and an escape velocity of 28.5 km/s.
In its orbital architecture around NGTS-4, NGTS-4 b completes one full revolution every 1.337 Earth days at a semi-major axis of 0.019 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 154.6 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 1650 K (+1377°C / +2511°F) and receiving 886.98 S⊕ (~1,207,185 W/m²), NGTS-4 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star NGTS-4 is classified as a stellar host with an effective photospheric temperature of 5,143 K, a radius of 0.84 R☉, a mass of 0.75 M☉, an estimated bolometric luminosity of 0.443 L☉. Stellar evolution modeling indicates a metallicity of [Fe/H] = -0.28 dex (metal-poor relative to the Sun). From Earth, NGTS-4 shines at apparent V-band magnitude 13.138 (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-4 |
| Spectral Type | Unclassified |
| Effective Temp (Teff) | 5,143 K |
| Stellar Radius | 0.8400 R☉ |
| Stellar Mass | 0.7500 M☉ |
| Bolometric Luminosity | 0.443 L☉ |
| Metallicity [Fe/H] | -0.280 dex |
| Stellar Age | — |
| Apparent Magnitude | V: 13.138 · G: 12.909 |
| System Architecture | 1 Star, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.019000 AU |
| Orbital Period | 1.337 days |
| Mean Orbital Velocity | 154.6 km/s |
| Orbital Eccentricity (e) | 0.00000 |
| Orbital Inclination (i) | 82.5000° |
| Mean Bulk Density | 3.53 g/cm³ (28.5 km/s vesc) |
| Insolation Flux | 886.9841 S⊕ (~1,207,185 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 915.000 LY (280.555 pc) |