TOI-521 b
Astrophysical Synthesis & Habitability Characterization
TOI-521 b is a confirmed super-earth exoplanet orbiting the star TOI-521, located approximately 198.8 light-years (60.94 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 0.1859% across the stellar disk), this world measures 1.98 Earth radii and has a measured mass of 5.3 Earth masses. Combining its mass and radius yields a mean bulk density of 3.76 g/cm³ (an intermediate density indicative of a deep water-ice mantle or dense volatile envelope), a surface gravity of 1.35 g⊕ (13.24 m/s²), and an escape velocity of 18.3 km/s.
In its orbital architecture around TOI-521, TOI-521 b completes one full revolution every 1.543 Earth days at a semi-major axis of 0.0195 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 137.5 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 794 K (+521°C / +970°F) and receiving 66.00 S⊕ (~89,826 W/m²), TOI-521 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star TOI-521 is classified as a low-mass red dwarf of spectral type M3 with an effective photospheric temperature of 3,544 K, a radius of 0.421 R☉, a mass of 0.42 M☉, an estimated bolometric luminosity of 0.025 L☉. Stellar evolution modeling indicates an estimated stellar age of 0.8 Gyr and a metallicity of [Fe/H] = -0.12 dex (metal-poor relative to the Sun). From Earth, TOI-521 shines at apparent V-band magnitude 14.691 (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-521 |
| Spectral Type | M3 |
| Effective Temp (Teff) | 3,544 K |
| Stellar Radius | 0.4210 R☉ |
| Stellar Mass | 0.4200 M☉ |
| Bolometric Luminosity | 0.025 L☉ |
| Metallicity [Fe/H] | -0.120 dex |
| Stellar Age | 0.800 Gyr |
| Apparent Magnitude | V: 14.691 · G: 13.586 |
| System Architecture | 1 Star, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.019500 AU |
| Orbital Period | 1.543 days |
| Mean Orbital Velocity | 137.5 km/s |
| Orbital Eccentricity (e) | 0.00000 |
| Orbital Inclination (i) | 88.6000° |
| Mean Bulk Density | 3.76 g/cm³ (18.3 km/s vesc) |
| Insolation Flux | 66.0000 S⊕ (~89,826 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 198.800 LY (60.943 pc) |