TOI-921 b
Astrophysical Synthesis & Habitability Characterization
TOI-921 b is a confirmed sub-neptune exoplanet orbiting the star TOI-921, located approximately 958.9 light-years (294.02 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 0.0805% across the stellar disk), this world measures 3.534 Earth radii (0.32 Jupiter radii) and has a measured mass of 12.2 Earth masses. Combining its mass and radius yields a mean bulk density of 1.52 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 0.98 g⊕ (9.61 m/s²), and an escape velocity of 20.8 km/s.
In its orbital architecture around TOI-921, TOI-921 b completes one full revolution every 5.129 Earth days.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 951 K (+678°C / +1252°F) and receiving 426.77 S⊕ (~580,832 W/m²), TOI-921 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star TOI-921 is classified as a stellar host with an effective photospheric temperature of 6,012 K, a radius of 1.1417 R☉, a mass of 1.13 M☉, an estimated bolometric luminosity of 1.528 L☉. Stellar evolution modeling indicates a metallicity of [Fe/H] = -0.058 dex (near-solar heavy-element abundance). From Earth, TOI-921 shines at apparent V-band magnitude 11.813 (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-921 |
| Spectral Type | Unclassified |
| Effective Temp (Teff) | 6,012 K |
| Stellar Radius | 1.1417 R☉ |
| Stellar Mass | 1.1300 M☉ |
| Bolometric Luminosity | 1.528 L☉ |
| Metallicity [Fe/H] | -0.058 dex |
| Stellar Age | — |
| Apparent Magnitude | V: 11.813 · G: 11.634 |
| System Architecture | 1 Star, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | — |
| Orbital Period | 5.129 days |
| Orbital Eccentricity (e) | Circular (0.00) |
| Orbital Inclination (i) | 86.5756° |
| Mean Bulk Density | 1.52 g/cm³ (20.8 km/s vesc) |
| Insolation Flux | 426.7683 S⊕ (~580,832 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 958.900 LY (294.015 pc) |