Astronomers Unveil TOI-5734 b, a New Hot Sub-Neptune Exoplanet

An international team of astronomers has successfully discovered a new exoplanet, designated TOI-5734 b, which is classified as a hot sub-Neptune. This planet, located approximately 106 light years from Earth, is notably about two times larger and nine times more massive than our planet. The findings were published on February 20, 2026, on the arXiv pre-print server.

Discovery and Characteristics of TOI-5734 b

The discovery was made using data from the Transiting Exoplanet Survey Satellite (TESS) and the High Accuracy Radial velocity Planet Searcher for the Northern Hemisphere (HARPS-N). The host star, known as TOI-5734 or TIC 9989136, is a relatively young K dwarf star with an effective temperature of approximately 4,750 K. Astronomers first identified a potential transit signal from this star in 2022, prompting follow-up observations led by Simone Filomeno from the Astronomical Observatory of Rome, Italy.

“In this paper, we present the detection and characterization of the transiting young planetary system TOI-5734 (TIC 9989136),” the researchers stated, highlighting their use of a combination of data from three TESS sectors and spectroscopic measurements from the HARPS-N spectrograph at the Galileo National Telescope.

Planetary Properties and Future Evolution

TOI-5734 b has a radius of about 2.1 Earth radii, with a mass measuring 9.1 Earth masses. This results in a density that is slightly less than that of Earth. The exoplanet completes an orbit around its host star every 6.18 days, situated at a distance of approximately 0.06 AU.

The estimated equilibrium temperature of TOI-5734 b is around 688 K, supporting its classification as a hot sub-Neptune with Earth-like density. The astronomers noted that its characteristics place it at the upper edge of the so-called “radius valley,” a range where there is a notable scarcity of planets with radii between 1.5 and 2.0 Earth radii.

Regarding its chemical composition, the researchers suggest that TOI-5734 b is likely a rocky planet that has significantly lost its primary atmosphere. They also propose a scenario where the planet could evolve into a “water world,” but anticipate that it will completely lose its primordial envelope within 300 million years.

The research provides insights into the past evolution of TOI-5734 b, indicating that the planet may have migrated from a region with larger radii in the mass-radius diagram to its current position near the radius gap.

The findings contribute significantly to our understanding of exoplanets, especially those classified within the sub-Neptune category. As researchers continue to explore these distant worlds, discoveries like TOI-5734 b help outline the complexities of planetary systems beyond our solar system.

This article is based on the research conducted by Filomeno et al. and is part of ongoing efforts in the field of astronomy to uncover the mysteries of the universe.