LP 791-18

LP 791-18 is a cool M dwarf star in the constellation Crater, located away from Earth. The star is one of the smallest known stars to host exoplanets. In 2019 two exoplanets in transit around it were announced by TESS, and a third planet was discovered in Spitzer Space Telescope data in 2023.

Planetary system

The innermost planet, b, is a super-Earth and the outermost planet, c, is a mini-Neptune. They were discovered together in 2019. The middle planet, d, is an Earth-mass world discovered in 2023. It may potentially be tidally heated by interactions with planet c, which would lead to abundant volcanoes similar to Jupiter's moon Io. As the planet d is in the inner edge of the habitable zone, liquid water could condense on the side of the planet that faces away from the host star.
In 2021 planet c was suggested for atmospheric analysis by the James Webb Space Telescope. In 2025, by using JWST the atmosphere of planet c was found to be rich in haze and methane but without clear evidence for carbon dioxide, which is unlike that of other temperate sub-Neptune planets including K2-18b and TOI-270d.