TOI-5789 c
Astrophysical Synthesis & Habitability Characterization
TOI-5789 c is a confirmed sub-neptune exoplanet orbiting the star TOI-5789, located approximately 66.7 light-years (20.46 parsecs) from the Solar System. First announced in 2026 by Transiting Exoplanet Survey Satellite (TESS) using the Transit detection technique (producing an estimated primary transit depth of 0.0991% across the stellar disk), this world measures 2.86 Earth radii and has a measured mass of 5 Earth masses. Combining its mass and radius yields a mean bulk density of 1.18 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 0.61 g⊕ (5.98 m/s²), and an escape velocity of 14.8 km/s.
In its orbital architecture around TOI-5789, TOI-5789 c completes one full revolution every 12.928 Earth days at a semi-major axis of 0.1009 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 84.9 km/s (compared to Earth's 29.8 km/s). Its moderate orbital eccentricity of e = 0.067 carries the world between 0.0941 AU at periapsis and 0.1077 AU at apoapsis, driving measurable seasonal insolation cycles.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 718 K (+445°C / +833°F) and receiving 8.72 S⊕ (~11,867 W/m²), TOI-5789 c orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star TOI-5789 is classified as an orange K-type star of spectral type K1 V with an effective photospheric temperature of 5,185 K, a radius of 0.833 R☉, a mass of 0.821 M☉, an estimated bolometric luminosity of 0.45 L☉. Stellar evolution modeling indicates an estimated stellar age of 9.4 Gyr and a metallicity of [Fe/H] = -0.12 dex (metal-poor relative to the Sun). From Earth, TOI-5789 shines at apparent V-band magnitude 7.351 (accessible to binoculars and small amateur telescopes) in the Northern celestial hemisphere. The TOI-5789 system is a multi-planet architecture hosting 4 confirmed worlds, with TOI-5789 c sharing its stellar neighborhood alongside TOI-5789 b, TOI-5789 d, TOI-5789 e.
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-5789 |
| Spectral Type | K1 V |
| Effective Temp (Teff) | 5,185 K |
| Stellar Radius | 0.8330 R☉ |
| Stellar Mass | 0.8210 M☉ |
| Bolometric Luminosity | 0.45 L☉ |
| Metallicity [Fe/H] | -0.120 dex |
| Stellar Age | 9.400 Gyr |
| Apparent Magnitude | V: 7.351 · G: 7.100 |
| System Architecture | 1 Star, 4 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.100900 AU |
| Orbital Period | 12.928 days |
| Mean Orbital Velocity | 84.9 km/s |
| Orbital Eccentricity (e) | 0.06700 |
| Orbital Inclination (i) | 88.0200° |
| Mean Bulk Density | 1.18 g/cm³ (14.8 km/s vesc) |
| Insolation Flux | 8.7194 S⊕ (~11,867 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 66.700 LY (20.458 pc) |