TOI-6478 b
Astrophysical Synthesis & Habitability Characterization
TOI-6478 b is a confirmed sub-neptune exoplanet orbiting the star TOI-6478, located approximately 125.9 light-years (38.61 parsecs) from the Solar System. First announced in 2025 by Transiting Exoplanet Survey Satellite (TESS) using the Transit detection technique (producing an estimated primary transit depth of 3.2481% across the stellar disk), this world measures 4.6 Earth radii (0.41 Jupiter radii) and has a measured mass of 19.2 Earth masses. Combining its mass and radius yields a mean bulk density of 1.09 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 0.91 g⊕ (8.92 m/s²), and an escape velocity of 22.9 km/s.
In its orbital architecture around TOI-6478, TOI-6478 b completes one full revolution every 34.005 Earth days at a semi-major axis of 0.1136 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 36.3 km/s (compared to Earth's 29.8 km/s).
☁️ Atmospheric Regime (Volatile / Gas Envelope): With a radius of 4.600 R⊕, TOI-6478 b exceeds the empirical ~1.8–2.2 R⊕ Fulton radius valley threshold, indicating a substantial hydrogen-helium or supercritical volatile envelope without a conventional solid terrestrial surface.
The host star TOI-6478 is classified as a low-mass red dwarf of spectral type M4.0+/-0.5 with an effective photospheric temperature of 3,230 K, a radius of 0.234 R☉, a mass of 0.23 M☉, an estimated bolometric luminosity of 0.00535 L☉. Stellar evolution modeling indicates an estimated stellar age of 6 Gyr and a metallicity of [Fe/H] = -0.53 dex (metal-poor relative to the Sun). From Earth, TOI-6478 shines at apparent V-band magnitude 15.99 (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: Transiting Exoplanet Survey Satellite (TESS) · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | TOI-6478 |
| Spectral Type | M4.0+/-0.5 |
| Effective Temp (Teff) | 3,230 K |
| Stellar Radius | 0.2340 R☉ |
| Stellar Mass | 0.2300 M☉ |
| Bolometric Luminosity | 0.00535 L☉ |
| Metallicity [Fe/H] | -0.530 dex |
| Stellar Age | 6.000 Gyr |
| Apparent Magnitude | V: 15.990 · G: 14.313 |
| System Architecture | 2 Stars, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.113600 AU |
| Orbital Period | 34.005 days |
| Mean Orbital Velocity | 36.3 km/s |
| Orbital Eccentricity (e) | Circular (0.00) |
| Orbital Inclination (i) | 89.8980° |
| Mean Bulk Density | 1.09 g/cm³ (22.9 km/s vesc) |
| Insolation Flux | 0.0003 S⊕ (~0 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 125.900 LY (38.606 pc) |