TOI-125 d
Astrophysical Synthesis & Habitability Characterization
TOI-125 d is a confirmed sub-neptune exoplanet orbiting the star TOI-125, located approximately 362.2 light-years (111.06 parsecs) from the Solar System. First announced in 2020 by Transiting Exoplanet Survey Satellite (TESS) using the Transit detection technique (producing an estimated primary transit depth of 0.1003% across the stellar disk), this world measures 2.93 Earth radii and has a measured mass of 13.6 Earth masses. Combining its mass and radius yields a mean bulk density of 2.98 g/cm³ (an intermediate density indicative of a deep water-ice mantle or dense volatile envelope), a surface gravity of 1.58 g⊕ (15.49 m/s²), and an escape velocity of 24.1 km/s.
In its orbital architecture around TOI-125, TOI-125 d completes one full revolution every 19.98 Earth days at a semi-major axis of 0.137 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 74.6 km/s (compared to Earth's 29.8 km/s). Its moderate orbital eccentricity of e = 0.168 carries the world between 0.114 AU at periapsis and 0.16 AU at apoapsis, driving measurable seasonal insolation cycles.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 638 K (+365°C / +689°F) and receiving 26.70 S⊕ (~36,339 W/m²), TOI-125 d orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star TOI-125 is classified as an orange K-type star of spectral type K0 V with an effective photospheric temperature of 5,320 K, a radius of 0.848 R☉, a mass of 0.859 M☉, an estimated bolometric luminosity of 0.517 L☉. Stellar evolution modeling indicates an estimated stellar age of 6.8 Gyr and a metallicity of [Fe/H] = -0.02 dex (near-solar heavy-element abundance). From Earth, TOI-125 shines at apparent V-band magnitude 11.023 (faint and requiring research-grade or CCD telescopic photometry) in the Southern celestial hemisphere. The TOI-125 system is a multi-planet architecture hosting 3 confirmed worlds, with TOI-125 d sharing its stellar neighborhood alongside TOI-125 b, TOI-125 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-125 |
| Spectral Type | K0 V |
| Effective Temp (Teff) | 5,320 K |
| Stellar Radius | 0.8480 R☉ |
| Stellar Mass | 0.8590 M☉ |
| Bolometric Luminosity | 0.517 L☉ |
| Metallicity [Fe/H] | -0.020 dex |
| Stellar Age | 6.800 Gyr |
| Apparent Magnitude | V: 11.023 · G: 10.718 |
| System Architecture | 1 Star, 3 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.137000 AU |
| Orbital Period | 19.98 days |
| Mean Orbital Velocity | 74.6 km/s |
| Orbital Eccentricity (e) | 0.16800 |
| Orbital Inclination (i) | 88.7950° |
| Mean Bulk Density | 2.98 g/cm³ (24.1 km/s vesc) |
| Insolation Flux | 26.7000 S⊕ (~36,339 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 362.200 LY (111.059 pc) |