L 98-59 b is an exoplanet having a size between that of the Earth and Mars and a mass only half that of Venus. It orbits L 98-59, a red dwarf star 34.6 light-years away in the constellation Volans. There are at least 4 (possibly 5) other planets in the system: L 98-59 c, d, e, f and the unconfirmed ".06". Its discovery was announced on 27 June 2019 in The Astronomical Journal and in a NASA press release. It was the smallest planet discovered by TESS until the discovery of LHS 1678 b, and was the lowest-mass planet whose mass had been measured using radial velocities until Proxima Centauri d was found in 2022.
L 98-59 b orbits its star in 2.25 days and stays so close to the star that it receives 22 times more energy than Earth receives from the Sun. There are 4 confirmed planets in the system but they are not in the habitable zone of the host star. The temperature of the planet detected by TESS is 330 ðC. In 2022, transmission spectroscopy indicated that the planet has either no atmosphere or an opaque atmosphere with high-altitude hazes.
Transmission spectroscopy observations with the James Webb Space Telescope NIRSpec published in 2025 favor the presence of a sulfur dioxide atmosphere. This is likely driven by volcanism, implying that L 98-59 b experiences at least eight times as much volcanism and tidal heating as Io.