Gliese 436 b is an exoplanet that orbits the red dwarf star Gliese 436, located approximately 33 light-years away from Earth in the constellation Leo. It was discovered in 2004 and is classified as a "hot Neptune" due to its similar size to Neptune but much closer proximity to its star.

Gliese 436 b has a mass about 22 times that of Earth and a radius about 4 times larger. It orbits its star at a distance of only 3.2 million miles (5.2 million kilometers), completing one orbit in just 2.6 Earth days. This close proximity to its star has caused the planet to become tidally locked, meaning one side always faces the star while the other side remains in perpetual darkness.

The extreme heat and proximity to its star have also caused Gliese 436 b to have a unique atmosphere. It is believed to have a thick layer of hydrogen and helium surrounding it, which creates a "superheated steam" atmosphere. The planet's surface temperature is estimated to be around 800 degrees Fahrenheit (427 degrees Celsius).

Gliese 436 b has been studied extensively by astronomers to better understand the characteristics and behavior of exoplanets. Its close proximity and unique atmosphere make it an interesting object of study in the field of exoplanet research.