K2-72 e is a planet a little larger than Earth that orbits within the habitable zone of its star, the range of distances where liquid water could last on a surface. It is the outermost of four planets around K2-72, a red dwarf about 220 light-years away, and passes in front of the star every 24.2 days.
It was discovered in data from NASA's K2 mission, which watched for the small dips in starlight as planets crossed their stars, and was validated in 2016 by a team led by Ian Crossfield along with its three siblings. In 2017 a team led by Courtney Dressing measured the star with infrared spectroscopy, which revised the planet's size to about 1.29 times Earth's. They found it to be one of three planets in their sample of 79 that orbit within optimistic habitable-zone limits, set between the point where Venus may once have had water and the point where early Mars may have.
According to the NASA Exoplanet Archive, it receives about 1.2 times the light Earth gets from the Sun, with an estimated equilibrium temperature of about 290 kelvin. That is promising, but much is unknown. Its mass has not been measured; the archive's figure of about 2.2 Earth masses is an estimate from its size. Nothing is known about its atmosphere, and red dwarfs like K2-72 can flare in ways that strip a planet's air.