K2-72e

Lore & Background

K2-72e orbits the red dwarf star K2-72, which has a mass of 0.27 solar masses and a radius of 0.33 solar radii. The star's apparent magnitude is 15.309, making it too dim to be seen with the naked eye. The planet completes one orbit every 24 days at a distance of about 0.1 AU from its star, closer than Mercury is to the Sun. The planet is very likely tidally locked, with one hemisphere permanently facing the star and the opposite side in eternal darkness. It receives 11% more insolation than Earth does, so any oceans present are potentially vulnerable to boiling away, possibly reducing the chance of habitability.

Reader's Guide

K2-72e is notable as one of the first Earth-sized planets found in the habitable zone of a red dwarf star by the Kepler spacecraft's second mission. Its discovery, along with the other three planets in the K2-72 system, was announced in mid-July 2016. The planet's equilibrium temperature of 261 K and radius of 1.29 Earth radii suggest it is likely rocky, though its mass of 2.2 Earth masses depends on composition. The host star, a red dwarf with about a fifth the mass of the Sun, can live up to 1–2 trillion years, hundreds of times longer than the Sun. This longevity, combined with the planet's position in the habitable zone, makes K2-72e a target for studying potential habitability around low-mass stars. However, the 11% higher insolation than Earth and likely tidal locking present challenges for liquid water stability. The planet's significance lies in demonstrating that small, cool stars can host Earth-sized planets in temperate orbits, expanding the search for potentially habitable worlds.

Did You Know?

• K2-72e is the outermost of four planets discovered in the K2-72 system.
• It is very likely tidally locked, with one side permanently facing its star.
• The host star K2-72 has an apparent magnitude of 15.309, invisible to the naked eye.