About this world
TOI-2257 b is a sub-Neptune orbiting TOI-2257, a cool red dwarf (type M3) 188 light-years from Earth. It is about 2.2 times the size of Earth. It completes an orbit every 35.2 days at 0.14 AU from its star, closer than Mercury is to the Sun, on a strongly elongated orbit (e = 0.5).
Its equilibrium temperature is about 256 K (−17 °C), which places it in the conservative habitable zone: the band where liquid water could exist on a rocky surface. By the "cosmic shoreline", it has likely held on to an atmosphere.
It was discovered in 2021 by transit with Transiting Exoplanet Survey Satellite (TESS). A planet crosses its star and dims it by a tiny, periodic fraction.