K2-32

K2-32 is a G9-type main sequence star slightly smaller and less massive than the sun. Four confirmed transiting exoplanets are known to orbit this star. A study of atmospheric escape from the planet K2-32b caused by high-energy stellar irradiation indicates that the star has always been a very slow rotator.

Discovery
The star K2-32 was initially found to have three transiting planet candidates by Andrew Vanderburg and collaborators in 2016. The innermost planet candidate, at that time, K2-32b was confirmed using radial velocity measurements made with the Keck telescope. Confirmation of planets c and d was made by Sinukoff et al. using adaptive optics imaging and computer analysis to eliminate possible false positives.

The Earth-sized planet K2-32e was discovered and validated by René Heller and team in 2019.

Characteristics
With periods of 4.34, 8.99, 20.66 and 31.71 days the four planets orbits are very close to a 1:2:5:7 orbital resonance chain. The densities of planets b, c, and d are between those of Saturn and Neptune, which suggests large and massive atmospheres. The planet K2-32e with a radius almost identical to that of the Earth is almost certainly a terrestrial planet. All four planets are well inside even the optimistic inner boundary of the habitable zone located at 0.58 astronomical units.