TOI-257 b

Astrophysical Synthesis & Habitability Characterization

TOI-257 b is a confirmed gas giant exoplanet orbiting the star TOI-257, located approximately 250.8 light-years (76.9 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 0.1237% across the stellar disk), this world measures 7.163 Earth radii (0.64 Jupiter radii) and has a measured mass of 43.86 Earth masses (0.14 Jupiter masses). Combining its mass and radius yields a mean bulk density of 0.66 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 0.85 g⊕ (8.34 m/s²), and an escape velocity of 27.7 km/s.

In its orbital architecture around TOI-257, TOI-257 b completes one full revolution every 18.388 Earth days at a semi-major axis of 0.1528 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 90.4 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 1027 K (+754°C / +1389°F) and receiving 186.00 S⊕ (~253,146 W/m²), TOI-257 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.

The host star TOI-257 is classified as a stellar host with an effective photospheric temperature of 6,095 K, a radius of 1.867 R☉, a mass of 1.407 M☉, an estimated bolometric luminosity of 4.316 L☉. Stellar evolution modeling indicates a metallicity of [Fe/H] = 0.175 dex (metal-rich relative to the Sun). From Earth, TOI-257 shines at apparent V-band magnitude 7.57 (accessible to binoculars and small amateur telescopes) in the Southern celestial hemisphere.

Discovery Facility: Transiting Exoplanet Survey Satellite (TESS) · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).