TOI-5678 b
Astrophysical Synthesis & Habitability Characterization
TOI-5678 b is a confirmed sub-neptune exoplanet orbiting the star TOI-5678, located approximately 539.4 light-years (165.39 parsecs) from the Solar System. First announced in 2023 by Transiting Exoplanet Survey Satellite (TESS) using the Transit detection technique (producing an estimated primary transit depth of 0.2303% across the stellar disk), this world measures 4.91 Earth radii (0.44 Jupiter radii) and has a measured mass of 20 Earth masses. Combining its mass and radius yields a mean bulk density of 0.93 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 0.83 g⊕ (8.14 m/s²), and an escape velocity of 22.6 km/s.
In its orbital architecture around TOI-5678, TOI-5678 b completes one full revolution every 47.73 Earth days at a semi-major axis of 0.249 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 56.8 km/s (compared to Earth's 29.8 km/s). Its moderate orbital eccentricity of e = 0.14 carries the world between 0.2141 AU at periapsis and 0.2839 AU at apoapsis, driving measurable seasonal insolation cycles.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 513 K (+240°C / +464°F) and receiving 3.84 S⊕ (~5,222 W/m²), TOI-5678 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star TOI-5678 is classified as a solar-type yellow star of spectral type G7 V with an effective photospheric temperature of 5,485 K, a radius of 0.938 R☉, a mass of 0.905 M☉, an estimated bolometric luminosity of 0.714 L☉. Stellar evolution modeling indicates an estimated stellar age of 8.5 Gyr and a metallicity of [Fe/H] = 0 dex (near-solar heavy-element abundance). From Earth, TOI-5678 shines at apparent V-band magnitude 11.438 (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-5678 |
| Spectral Type | G7 V |
| Effective Temp (Teff) | 5,485 K |
| Stellar Radius | 0.9380 R☉ |
| Stellar Mass | 0.9050 M☉ |
| Bolometric Luminosity | 0.714 L☉ |
| Metallicity [Fe/H] | 0.000 dex |
| Stellar Age | 8.500 Gyr |
| Apparent Magnitude | V: 11.438 · G: 11.148 |
| System Architecture | 1 Star, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.249000 AU |
| Orbital Period | 47.73 days |
| Mean Orbital Velocity | 56.8 km/s |
| Orbital Eccentricity (e) | 0.14000 |
| Orbital Inclination (i) | 89.8300° |
| Mean Bulk Density | 0.93 g/cm³ (22.6 km/s vesc) |
| Insolation Flux | 3.8369 S⊕ (~5,222 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 539.400 LY (165.393 pc) |