L 98-59 d is the largest of the three transiting planets around L 98-59, a bright red dwarf about 35 light-years away, and the one with the strongest hints of an atmosphere. It orbits every 7.45 days and is about 1.63 times Earth's width. NASA's TESS satellite found it in 2019 together with L 98-59 b and c, by watching for the small dips in starlight as each planet crossed its star.
Its mass, about 1.64 Earth masses, comes from a 2025 study led by Charles Cadieux that combined measurements of the star's wobble with transit timing: L 98-59 c and d pull on each other, so their transits arrive slightly early or late. For its size, that mass makes it less dense than its inner siblings. The study's models suggest water could make up around 16 percent of its mass; an earlier 2021 analysis by Olivier Demangeon's team had allowed up to 30 percent. Whether that means oceans, ice or steam is not known.
In 2024 a team led by Agnibha Banerjee analysed one transit observed by the James Webb Space Telescope and found the spectrum consistent with a heavy atmosphere, possibly containing hydrogen sulfide and sulfur dioxide, gases that could point to volcanoes. They called these signs tentative. In 2026 a team led by Connor Cheverall observed the planet from the ground with the IGRINS spectrograph on the Gemini South telescope and found further evidence for hydrogen sulfide, at a confidence of up to 3.9 sigma. That is the first molecule inferred in a super-Earth's atmosphere from the ground. More observations are needed to confirm it. At an equilibrium temperature of about 420 kelvin, it is too hot for liquid water on its surface.