About this world
KMT-2021-BLG-1253L b is a Neptune-like planet orbiting KMT-2021-BLG-1253L, a star 21.7 thousand light-years from Earth. It is about 4.6 times the size of Earth (its size estimated from its mass) and holds 19 Earth masses.
At its size it almost certainly keeps a deep envelope of hydrogen and helium.
It was discovered in 2022 by microlensing with KMTNet. A foreground star's gravity magnifies a background star; a planet adds a blip.