New Insights into the Mass and Composition of Exoplanet TOI-654 b

Researchers have reported significant findings regarding TOI-654 b, a sub-Neptune exoplanet transiting a mid-M dwarf star, enhancing our understanding of its mass and composition. The study, conducted by a team led by Kai Ikuta and published in the Preprints of Astrophysics on July 23, 2025, utilized the InfraRed Doppler (IRD) instrument on the Subaru Telescope, alongside data from the Transit Exoplanet Survey Satellite (TESS) and the Multicolor Simultaneous Camera for studying Atmospheres of Transiting exoplanets (MuSCAT). The findings indicate that TOI-654 b has a mass of approximately 8.71 ± 1.25 Earth masses and a radius of 2.378 ± 0.089 Earth radii, suggesting it is situated within the radius valley, an area of interest for the evolution of small planets.

The significance of this research lies in its contributions to the understanding of exoplanetary atmospheres and their potential habitability. According to Dr. Norio Narita, Associate Professor of Astronomy at the University of Tokyo, "The precise mass determination of TOI-654 b enables us to better constrain the atmospheric properties, which are essential for future spectroscopic observations using the James Webb Space Telescope and the Ariel mission." The atmospheric composition can provide insights into the planet's formation history and its potential to host life.

The observational campaign included multicolor simultaneous light curves that were obtained on two separate occasions in early 2021, allowing for a robust analysis of the planet’s transit. This involved fitting the data to a transit model, which facilitated the extraction of key parameters regarding the planet and its host star. The research offers a glimpse into the characteristics of planets located in the Neptune desert, a region in parameter space where fewer Neptune-sized planets are found, thus raising questions about their formation and evolution.

Experts have noted that further observations are crucial to understanding the atmospheric composition of TOI-654 b. Dr. Takuya Takarada, a researcher at the National Astronomical Observatory of Japan, emphasized the importance of upcoming observations, stating, "The atmospheric data we can gather will reveal whether TOI-654 b has a volatile-rich atmosphere or if it is composed primarily of heavier materials."

This discovery aligns with ongoing research into the diverse characteristics of exoplanets and their formation mechanisms. As astronomers continue to unveil the conditions surrounding these distant worlds, TOI-654 b stands out as a promising candidate for future studies. The implications of these findings extend to the broader field of planetary science, where understanding various planetary compositions can elucidate the potential for life elsewhere in the universe.

In conclusion, the study of TOI-654 b not only enhances our understanding of sub-Neptune planets but also provides a valuable reference point for future exoplanetary research and exploration initiatives. The continued investigation into the atmospheres of such planets will be pivotal in our quest to uncover the mysteries of the universe and the potential for extraterrestrial life.