About this world
KMT-2017-BLG-2509L b is a gas giant orbiting KMT-2017-BLG-2509L, a star 23 thousand light-years from Earth. It is about 1.2 times the size of Jupiter (its size estimated from its mass) and holds 2.1 Jupiter masses.
At its size it almost certainly keeps a deep envelope of hydrogen and helium.
It was discovered in 2021 by microlensing with KMTNet. A foreground star's gravity magnifies a background star; a planet adds a blip.