TOI-5261 b
Astrophysical Synthesis & Habitability Characterization
TOI-5261 b is a confirmed gas giant exoplanet orbiting the star TOI-5261, located approximately 1229.8 light-years (377.05 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 1.0851% across the stellar disk), this world measures 11.601 Earth radii (1.03 Jupiter radii) and has a measured mass of 3651.848 Earth masses (11.49 Jupiter masses). Combining its mass and radius yields a mean bulk density of 12.9 g/cm³ (an iron-enriched, high-compression rocky core), a surface gravity of 27.13 g⊕ (266.05 m/s²), and an escape velocity of 198.5 km/s.
In its orbital architecture around TOI-5261, TOI-5261 b completes one full revolution every 4.151 Earth days at a semi-major axis of 0.05134 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 134.6 km/s (compared to Earth's 29.8 km/s). Its moderate orbital eccentricity of e = 0.1585 carries the world between 0.0432 AU at periapsis and 0.0595 AU at apoapsis, driving measurable seasonal insolation cycles.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 1244 K (+971°C / +1780°F) and receiving 159.59 S⊕ (~217,205 W/m²), TOI-5261 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star TOI-5261 is classified as a stellar host with an effective photospheric temperature of 5,790 K, a radius of 1.021 R☉, a mass of 1.037 M☉, an estimated bolometric luminosity of 1.051 L☉. Stellar evolution modeling indicates an estimated stellar age of 4.2 Gyr and a metallicity of [Fe/H] = 0.254 dex (metal-rich relative to the Sun). From Earth, TOI-5261 shines at apparent V-band magnitude 12.68 (faint and requiring research-grade or CCD telescopic photometry) in the Northern 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-5261 |
| Spectral Type | Unclassified |
| Effective Temp (Teff) | 5,790 K |
| Stellar Radius | 1.0210 R☉ |
| Stellar Mass | 1.0370 M☉ |
| Bolometric Luminosity | 1.051 L☉ |
| Metallicity [Fe/H] | 0.254 dex |
| Stellar Age | 4.200 Gyr |
| Apparent Magnitude | V: 12.680 · G: 12.602 |
| System Architecture | 1 Star, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.051340 AU |
| Orbital Period | 4.151 days |
| Mean Orbital Velocity | 134.6 km/s |
| Orbital Eccentricity (e) | 0.15850 |
| Orbital Inclination (i) | 86.0700° |
| Mean Bulk Density | 12.9 g/cm³ (198.5 km/s vesc) |
| Insolation Flux | 159.5920 S⊕ (~217,205 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 1229.800 LY (377.054 pc) |