TOI-1221 b
Astrophysical Synthesis & Habitability Characterization
TOI-1221 b is a confirmed sub-neptune exoplanet orbiting the star TOI-1221, located approximately 451.4 light-years (138.41 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 0.067% across the stellar disk), this world measures 2.91 Earth radii and has a measured mass of 1112.399 Earth masses (3.5 Jupiter masses). Combining its mass and radius yields a mean bulk density of 248.91 g/cm³ (an iron-enriched, high-compression rocky core), a surface gravity of 131.36 g⊕ (1288.2 m/s²), and an escape velocity of 218.7 km/s.
In its orbital architecture around TOI-1221, TOI-1221 b completes one full revolution every 91.683 Earth days at a semi-major axis of 0.387 AU (situated at an orbital separation between Mercury's 0.39 AU and Venus's 0.72 AU). Its mean orbital velocity is approximately 45.9 km/s (compared to Earth's 29.8 km/s). Its moderate orbital eccentricity of e = 0.21 carries the world between 0.3057 AU at periapsis and 0.4683 AU at apoapsis, driving measurable seasonal insolation cycles.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 440 K (+167°C / +333°F) and receiving 6.06 S⊕ (~8,248 W/m²), TOI-1221 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star TOI-1221 is classified as a stellar host with an effective photospheric temperature of 5,592 K, a radius of 1.031 R☉, a mass of 0.93 M☉, an estimated bolometric luminosity of 0.933 L☉. Stellar evolution modeling indicates an estimated stellar age of 10 Gyr and a metallicity of [Fe/H] = 0.06 dex (metal-rich relative to the Sun). From Earth, TOI-1221 shines at apparent V-band magnitude 10.494 (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-1221 |
| Spectral Type | Unclassified |
| Effective Temp (Teff) | 5,592 K |
| Stellar Radius | 1.0310 R☉ |
| Stellar Mass | 0.9300 M☉ |
| Bolometric Luminosity | 0.933 L☉ |
| Metallicity [Fe/H] | 0.060 dex |
| Stellar Age | 10.000 Gyr |
| Apparent Magnitude | V: 10.494 · G: 10.526 |
| System Architecture | 1 Star, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.387000 AU |
| Orbital Period | 91.683 days |
| Mean Orbital Velocity | 45.9 km/s |
| Orbital Eccentricity (e) | 0.21000 |
| Orbital Inclination (i) | 89.7500° |
| Mean Bulk Density | 248.91 g/cm³ (218.7 km/s vesc) |
| Insolation Flux | 6.0600 S⊕ (~8,248 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 451.400 LY (138.411 pc) |