TOI-431 d
Astrophysical Synthesis & Habitability Characterization
TOI-431 d is a confirmed sub-neptune exoplanet orbiting the star TOI-431, located approximately 106.2 light-years (32.57 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 0.1703% across the stellar disk), this world measures 3.29 Earth radii (0.29 Jupiter radii) and has a measured mass of 9.9 Earth masses. Combining its mass and radius yields a mean bulk density of 1.53 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 0.91 g⊕ (8.92 m/s²), and an escape velocity of 19.4 km/s.
In its orbital architecture around TOI-431, TOI-431 d completes one full revolution every 12.461 Earth days at a semi-major axis of 0.098 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 85.6 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 633 K (+360°C / +680°F) and receiving 28.36 S⊕ (~38,596 W/m²), TOI-431 d orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star TOI-431 is classified as a stellar host with an effective photospheric temperature of 4,850 K, a radius of 0.731 R☉, a mass of 0.78 M☉, an estimated bolometric luminosity of 0.265 L☉. Stellar evolution modeling indicates a metallicity of [Fe/H] = 0.2 dex (metal-rich relative to the Sun). From Earth, TOI-431 shines at apparent V-band magnitude 9.12 (accessible to binoculars and small amateur telescopes) in the Southern celestial hemisphere. The TOI-431 system is a multi-planet architecture hosting 3 confirmed worlds, with TOI-431 d sharing its stellar neighborhood alongside TOI-431 b, TOI-431 c.
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-431 |
| Spectral Type | Unclassified |
| Effective Temp (Teff) | 4,850 K |
| Stellar Radius | 0.7310 R☉ |
| Stellar Mass | 0.7800 M☉ |
| Bolometric Luminosity | 0.265 L☉ |
| Metallicity [Fe/H] | 0.200 dex |
| Stellar Age | — |
| Apparent Magnitude | V: 9.120 · G: 8.792 |
| System Architecture | 1 Star, 3 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.098000 AU |
| Orbital Period | 12.461 days |
| Mean Orbital Velocity | 85.6 km/s |
| Orbital Eccentricity (e) | 0.00000 |
| Orbital Inclination (i) | 89.7000° |
| Mean Bulk Density | 1.53 g/cm³ (19.4 km/s vesc) |
| Insolation Flux | 28.3588 S⊕ (~38,596 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 106.200 LY (32.569 pc) |