TOI-1728 b
Astrophysical Synthesis & Habitability Characterization
TOI-1728 b is a confirmed sub-neptune exoplanet orbiting the star TOI-1728, located approximately 198.3 light-years (60.8 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 0.55% across the stellar disk), this world measures 5.05 Earth radii (0.45 Jupiter radii) and has a measured mass of 26.78 Earth masses. Combining its mass and radius yields a mean bulk density of 1.15 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 1.05 g⊕ (10.3 m/s²), and an escape velocity of 25.8 km/s.
In its orbital architecture around TOI-1728, TOI-1728 b completes one full revolution every 3.492 Earth days at a semi-major axis of 0.0391 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 121.8 km/s (compared to Earth's 29.8 km/s). Its moderate orbital eccentricity of e = 0.057 carries the world between 0.0369 AU at periapsis and 0.0413 AU at apoapsis, driving measurable seasonal insolation cycles.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 767 K (+494°C / +921°F) and receiving 57.78 S⊕ (~78,639 W/m²), TOI-1728 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star TOI-1728 is classified as a low-mass red dwarf of spectral type M0 with an effective photospheric temperature of 3,980 K, a radius of 0.6243 R☉, a mass of 0.646 M☉, an estimated bolometric luminosity of 0.088 L☉. Stellar evolution modeling indicates an estimated stellar age of 7.1 Gyr and a metallicity of [Fe/H] = 0.25 dex (metal-rich relative to the Sun). From Earth, TOI-1728 shines at apparent V-band magnitude 12.39 (faint and requiring research-grade or CCD telescopic photometry) in the Northern 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-1728 |
| Spectral Type | M0 |
| Effective Temp (Teff) | 3,980 K |
| Stellar Radius | 0.6243 R☉ |
| Stellar Mass | 0.6460 M☉ |
| Bolometric Luminosity | 0.088 L☉ |
| Metallicity [Fe/H] | 0.250 dex |
| Stellar Age | 7.100 Gyr |
| Apparent Magnitude | V: 12.390 · G: 11.729 |
| System Architecture | 1 Star, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.039100 AU |
| Orbital Period | 3.492 days |
| Mean Orbital Velocity | 121.8 km/s |
| Orbital Eccentricity (e) | 0.05700 |
| Orbital Inclination (i) | 88.3100° |
| Mean Bulk Density | 1.15 g/cm³ (25.8 km/s vesc) |
| Insolation Flux | 57.7800 S⊕ (~78,639 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 198.300 LY (60.798 pc) |