TOI-2406 b
Astrophysical Synthesis & Habitability Characterization
TOI-2406 b is a confirmed sub-neptune exoplanet orbiting the star TOI-2406, located approximately 180.8 light-years (55.42 parsecs) from the Solar System. First announced in 2021 by Transiting Exoplanet Survey Satellite (TESS) using the Transit detection technique (producing an estimated primary transit depth of 1.652% across the stellar disk), this world measures 2.86 Earth radii and has a measured mass of 15.6 Earth masses. Combining its mass and radius yields a mean bulk density of 3.68 g/cm³ (an intermediate density indicative of a deep water-ice mantle or dense volatile envelope), a surface gravity of 1.91 g⊕ (18.73 m/s²), and an escape velocity of 26.1 km/s.
In its orbital architecture around TOI-2406, TOI-2406 b completes one full revolution every 3.077 Earth days at a semi-major axis of 0.02267 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 80.2 km/s (compared to Earth's 29.8 km/s). Its moderate orbital eccentricity of e = 0.17 carries the world between 0.0188 AU at periapsis and 0.0265 AU at apoapsis, driving measurable seasonal insolation cycles.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 449 K (+176°C / +349°F) and receiving 6.69 S⊕ (~9,105 W/m²), TOI-2406 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star TOI-2406 is classified as a low-mass red dwarf of spectral type M4 V with an effective photospheric temperature of 3,100 K, a radius of 0.204 R☉, a mass of 0.166 M☉, an estimated bolometric luminosity of 0.00345 L☉. Stellar evolution modeling indicates a metallicity of [Fe/H] = -0.26 dex (metal-poor relative to the Sun). From Earth, TOI-2406 shines at apparent Gaia G-band magnitude 15.696 (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-2406 |
| Spectral Type | M4 V |
| Effective Temp (Teff) | 3,100 K |
| Stellar Radius | 0.2040 R☉ |
| Stellar Mass | 0.1660 M☉ |
| Bolometric Luminosity | 0.00345 L☉ |
| Metallicity [Fe/H] | -0.260 dex |
| Stellar Age | — |
| Apparent Magnitude | · G: 15.696 |
| System Architecture | 1 Star, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.022670 AU |
| Orbital Period | 3.077 days |
| Mean Orbital Velocity | 80.2 km/s |
| Orbital Eccentricity (e) | 0.17000 |
| Orbital Inclination (i) | 89.8000° |
| Mean Bulk Density | 3.68 g/cm³ (26.1 km/s vesc) |
| Insolation Flux | 6.6900 S⊕ (~9,105 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 180.800 LY (55.419 pc) |