TOI-128.01
Astrophysical Synthesis & Habitability Characterization
TOI-128.01 is a confirmed sub-neptune exoplanet orbiting the star TOI-128, located approximately 223.3 light-years (68.47 parsecs) from the Solar System. First announced in 2024 by Transiting Exoplanet Survey Satellite (TESS) using the Transit detection technique (producing an estimated primary transit depth of 0.0324% across the stellar disk), this world measures 2.219 Earth radii and has a measured mass of 5.56 Earth masses. Combining its mass and radius yields a mean bulk density of 2.81 g/cm³ (an intermediate density indicative of a deep water-ice mantle or dense volatile envelope), a surface gravity of 1.13 g⊕ (11.08 m/s²), and an escape velocity of 17.7 km/s.
In its orbital architecture around TOI-128, TOI-128.01 completes one full revolution every 4.94 Earth days at a semi-major axis of 0.05381 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 118.5 km/s (compared to Earth's 29.8 km/s).
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 1345 K (+1072°C / +1962°F) and receiving 182.41 S⊕ (~248,255 W/m²), TOI-128.01 orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star TOI-128 is classified as a stellar host with an effective photospheric temperature of 6,086 K, a radius of 1.13 R☉, a mass of 0.852 M☉, an estimated bolometric luminosity of 1.572 L☉. From Earth, TOI-128 shines at apparent V-band magnitude 8.44 (accessible to binoculars and small amateur telescopes) 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-128 |
| Spectral Type | Unclassified |
| Effective Temp (Teff) | 6,086 K |
| Stellar Radius | 1.1300 R☉ |
| Stellar Mass | 0.8520 M☉ |
| Bolometric Luminosity | 1.572 L☉ |
| Metallicity [Fe/H] | — |
| Stellar Age | — |
| Apparent Magnitude | V: 8.440 · G: 8.372 |
| System Architecture | 1 Star, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.053810 AU |
| Orbital Period | 4.94 days |
| Mean Orbital Velocity | 118.5 km/s |
| Orbital Eccentricity (e) | Circular (0.00) |
| Orbital Inclination (i) | — |
| Mean Bulk Density | 2.81 g/cm³ (17.7 km/s vesc) |
| Insolation Flux | 182.4060 S⊕ (~248,255 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 223.300 LY (68.473 pc) |