A rocky world 91 light-years away could be JWST’s next atmospheric target

An international team of astronomers using NASA’s Transiting Exoplanet Survey Satellite (TESS) has confirmed the existence of a new Earth-sized planet orbiting a nearby M-dwarf star just 91.8 light-years away. The discovery adds a valuable entry to the growing catalog of rocky worlds around small stars — and opens a window into the atmospheric physics of planets not so different from our own.

A nearby M-dwarf under the TESS spotlight

The host star, designated TOI-4616, is a mid-M dwarf of spectral type M4 — a dim, red star roughly 19% the size and mass of our Sun. Its effective temperature sits at around 3,150 K, its metallicity is approximately −0.32 dex, and its estimated age falls between 300 and 800 million years, making it a relatively young system by stellar standards.

TESS detected a transit signal in the light curve of TOI-4616 with a period of approximately 1.5 days. Follow-up observations, led by Francis Zong Lang and colleagues at the University of Bern (Switzerland), confirmed the planetary nature of the signal through a combination of TESS photometry, ground-based multi-band transit observations, high-resolution imaging, and optical/near-infrared spectroscopy.

TOI-4616 b: properties of an Earth-like world

The confirmed planet, TOI-4616 b, has a radius of approximately 1.22 Earth radii and an estimated mass between 1.5 and 3.0 Earth masses — placing it firmly in the super-Earth or rocky planet regime. It completes one orbit around its host star every 37.2 hours, and its equilibrium temperature is estimated at 525 K (~252 °C), making it too hot for liquid water but thermally interesting for atmospheric studies.

A stripped envelope — or a surviving atmosphere?

The researchers propose that TOI-4616 b likely lost its primordial hydrogen/helium envelope through atmospheric escape processes. However, a compact secondary atmosphere — potentially outgassed from the planet’s interior — may have persisted. This makes TOI-4616 b an excellent candidate for atmospheric characterization with the James Webb Space Telescope (JWST), which could detect spectral signatures of any remaining atmospheric gases during transit.

Why this discovery matters

TOI-4616 b is classified as a rocky world orbiting a mid-M dwarf, a class of planetary systems that TESS has been systematically targeting since its launch in 2018. To date, TESS has scanned approximately 200,000 of the brightest stars near the Sun, identifying more than 7,900 candidate exoplanets (TESS Objects of Interest, or TOIs), of which 760 have been confirmed.

The authors highlight TOI-4616 b as a benchmark system for comparative planetology — specifically for studying terrestrial planets around mid-M dwarfs, a population that remains poorly characterized. As JWST continues its atmospheric survey program, Earth-sized planets like TOI-4616 b around nearby, small stars represent some of the most accessible targets for transmission spectroscopy.

Source

Zong Lang, F. et al. (2026). TOI-4616 b: an Earth-sized planet transiting a nearby mid-M dwarf. arXiv preprint. DOI: 10.48550/arxiv.2603.10905

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