TOI-1408 c
Astrophysical Synthesis & Habitability Characterization
TOI-1408 c is a confirmed sub-neptune exoplanet orbiting the star TOI-1408, located approximately 454.9 light-years (139.48 parsecs) from the Solar System. First announced in 2024 by Transiting Exoplanet Survey Satellite (TESS) using the Transit Timing Variations detection technique (producing an estimated primary transit depth of 0.0177% across the stellar disk), this world measures 2.22 Earth radii and has a measured mass of 7.6 Earth masses. Combining its mass and radius yields a mean bulk density of 3.83 g/cm³ (an intermediate density indicative of a deep water-ice mantle or dense volatile envelope), a surface gravity of 1.54 g⊕ (15.1 m/s²), and an escape velocity of 20.7 km/s.
In its orbital architecture around TOI-1408, TOI-1408 c completes one full revolution every 2.166 Earth days at a semi-major axis of 0.03587 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 180.1 km/s (compared to Earth's 29.8 km/s). Its moderate orbital eccentricity of e = 0.1353 carries the world between 0.031 AU at periapsis and 0.0407 AU at apoapsis, driving measurable seasonal insolation cycles.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 1864 K (+1591°C / +2896°F) and receiving 2,005.35 S⊕ (~2,729,281 W/m²), TOI-1408 c orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star TOI-1408 is classified as a warm F-type star of spectral type F8 V with an effective photospheric temperature of 6,117 K, a radius of 1.53 R☉, a mass of 1.312 M☉, an estimated bolometric luminosity of 2.941 L☉. Stellar evolution modeling indicates an estimated stellar age of 2.7 Gyr and a metallicity of [Fe/H] = 0.25 dex (metal-rich relative to the Sun). From Earth, TOI-1408 shines at apparent V-band magnitude 9.27 (accessible to binoculars and small amateur telescopes) in the Northern celestial hemisphere. The TOI-1408 system is a multi-planet architecture hosting 2 confirmed worlds, with TOI-1408 c sharing its stellar neighborhood alongside TOI-1408 b.
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-1408 |
| Spectral Type | F8 V |
| Effective Temp (Teff) | 6,117 K |
| Stellar Radius | 1.5300 R☉ |
| Stellar Mass | 1.3120 M☉ |
| Bolometric Luminosity | 2.941 L☉ |
| Metallicity [Fe/H] | 0.250 dex |
| Stellar Age | 2.700 Gyr |
| Apparent Magnitude | V: 9.270 · G: 9.188 |
| System Architecture | 1 Star, 2 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.035870 AU |
| Orbital Period | 2.166 days |
| Mean Orbital Velocity | 180.1 km/s |
| Orbital Eccentricity (e) | 0.13530 |
| Orbital Inclination (i) | 82.6000° |
| Mean Bulk Density | 3.83 g/cm³ (20.7 km/s vesc) |
| Insolation Flux | 2005.3500 S⊕ (~2,729,281 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 454.900 LY (139.484 pc) |