Labeled L 98-59F, this exoplanet is an ultra-terrestrial with a minimum mass of 2.8 times that of Earth, orbiting within the habitable zone of the small red dwarf star L 98-59 every 23 days.
Artistic impressions of the L 98-59 Planetary System, with the habitable zone Super Earth L 98-59F in the foreground. Image credit: Benoît Gougeon/Udem.
L 98-59, also known as TOI-175 and TIC 307210830, is an M-type star with roughly one-third the mass of the Sun.
This stellar system is located approximately 34.5 light years away in the southern constellation of Volans.
It contains three transiting exoplanets discovered by TESS in 2019, along with an outer planet confirmed in 2021 using the ESO’s ESPRESSO spectrograph, with orbital periods of 2.25, 3.7, and 7.45 days.
The planets vary in size (0.8-1.6 times Earth’s radius), mass (0.5-3 times Earth’s mass), and potential compositions, likely leaning towards being water-rich.
In a recent study, astronomer Charles Cadigg and colleagues reanalyzed data from TESS, ESPRESSO, HARPS, and the Webb Space Telescope at the University of Montreal and the Exoplanetary Institute.
They achieved unprecedented accuracy in determining the sizes and masses of the planets.
“We refined the radii of L 98-59B, C, and D to 0.84, 1.33, and 1.63 Earth radii, respectively,” they reported.
“Our updated mass estimates are 0.46 Earth mass for L 98-59B, 2.0 for L 98-59C, and 1.64 for L 98-59D, with a minimum mass of 2.82 for L 98-59F.”
Astronomers confirmed the existence of a fifth planet, L 98-59F, located within the habitable zone of the star, where liquid water could exist.
“This discovery is particularly thrilling as we uncover temperate planets within such a compact system,” Dr. Cadiw remarked.
“It emphasizes the remarkable diversity of planetary systems and bolsters the argument for studying potentially habitable worlds around low-mass stars.”
“These new findings provide the most comprehensive view of the intriguing L 98-59 system to date,” he added.
“This exemplifies the potential of combining data from space telescopes and precision instruments, creating a crucial target for future atmospheric studies with the NASA/ESA/CSA James Webb Space Telescope.”
Precise measurements revealed the almost circular orbit of the innermost planet, a configuration conducive for future atmospheric detection.
“The varied rocky worlds and range of planetary compositions make L 98-59 a unique laboratory to explore some of the field’s most pressing questions. Do Super-Earths and Sub-Neptunes form differently around low-mass stars?” queried Professor Renée Doyon of Montreal University, director of the Trottier Institute for Exoplanet Research.
The team’s paper is set to be published in The Astronomical Journal.
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Charles Caddy et al. 2025. Detailed architecture of the L98-59 system and confirmation of the fifth planet in the habitable zone. AJ in press; Arxiv: 2507.09343
Source: www.sci.news
