This isn’t just another rocky world orbiting a red dwarf—this one’s special

Astronomers have found an exoplanet that could serve as a benchmark in future studies. It’s a rocky planet orbiting an M-type star, and though these planets are plentiful, this one could serve as a benchmark for understanding other M-dwarf exoplanets and their atmospheres. According to the authors of a new study, this new exoplanet could serve as “a reference system for highly irradiated rocky planets.”

The new research is titled “TOI-4616 b: a benchmark Earth-sized planet transiting a nearby M4 dwarf,” and it’s been submitted to the Monthly Notices of the Royal Astronomical Society. The lead author is Francis Zong Lang, a doctoral researcher at the Center for Space and Habitability at the University of Bern in Switzerland. The paper is currently available on the arXiv preprint server.

With more than 6,000 confirmed exoplanets, our understanding of the exoplanet population is becoming more complete. There are still observational biases in the results, but some trends are emerging. One thing that’s becoming clear is the relationship between M dwarfs and rocky exoplanets.

Research shows that M dwarfs are the most prolific hosts for terrestrial exoplanets. In fact, many of these stars host multiple rocky planets, with the TRAPPIST-1 system being the most well-known example: it hosts seven rocky planets.

All of these rocky worlds around dim stars open up a window to studying exoplanet atmospheres.

“Rocky exoplanets are particularly abundant around M-type stars,” the authors of the new research write. “Their small radii and low luminosities provide favorable conditions for detecting transiting terrestrial planets and probing their atmospheric properties.”

“We report the discovery and statistical validation of TOI-4616 b, an Earth-sized planet transiting a nearby mid-M dwarf observed by the Transiting Exoplanet Survey Satellite (TESS),” the authors write.

The thing about rocky planets around M-dwarfs is that they typically orbit very close to their stars. This puts them in atmospheric peril, as powerful radiation and flaring can strip their atmospheres away. It’s even worse. M-dwarfs take up to 1 or 2 billion years to reach the main sequence. Prior to that, their luminosity is much higher, putting additional dissipative pressure on the atmospheres of any rocky planets orbiting them.

There’s some good news for these atmospheres, though. While primordial hydrogen-rich atmospheres are easier to remove, thicker atmospheres dominated by CO₂ might resist dissipation. Secondary atmospheres could also form through volcanism and outgassing long after the star has entered the main sequence. It’s also possible that a strong enough magnetic field can help a planet retain its atmosphere.

So there’s a lot of complexity around these atmospheres, and no clear conclusions. More study is the answer, and part of that is the ability to compare the atmospheres of these planets to a benchmark.

That’s what makes this discovery important.

“Owing to its proximity to Earth, well-constrained stellar properties, and extensive multi-band follow-up, TOI-4616 b constitutes a valuable benchmark system for comparative studies of terrestrial planets around mid-M dwarfs and for future atmospheric investigations,” the researchers explain.

TOI-4616 is about 91 light-years away. Its radius is about 0.1889 solar radii, its mass is about 0.1881 solar masses, and its temperature is about 3150 Kelvin. These are pretty typical characteristics for a cool, small M-dwarf.

The exoplanet, TOI-4616 b has a radius of 1.22 Earth radii and an orbital period of 1.55 days. Its equilibrium temperature is around 525 Kelvin. “This places TOI-4616 b in a regime intermediate between Earth-sized planets orbiting early M dwarfs and those around ultra-cool hosts,” the authors explain. Like other planets in this situation, the bulk of its atmosphere may be long gone.

But the fact that its atmosphere is in peril is what makes it such an interesting exoplanet.

“TOI-4616 b resides in an extreme irradiation environment for an Earth-sized planet orbiting a mid-M dwarf,” the researchers explain. “This makes it a particularly informative test case for models of atmospheric escape, interior composition, and volatile retention.”

It can serve as a benchmark for the study of terrestrial planets in these situations. The authors say it’s “well-suited for comparative investigations of planetary structure and evolution in the strongly irradiated regime.”

One of the reasons the JWST was built is to study exoplanet atmospheres. But not all M-dwarf Earth-like exoplanets are great targets for the space telescope. For many of them, we lack precise measurements of the star or are restricted to only a few transit measurements. And though all M-dwarfs are dim in comparison to sun-like stars, they still vary in luminosity.

TOI-4616 is well understood because it’s been observed for so long. Archival data dates back to 1954, so that means that there’s more than years of data, though obviously, the most detailed measurements were taken well after the 1950s. PanSTARRS observed it in 2011 and SNO/Artemis in 2025. A host of other telescopes with different capabilities have observed it over the decades.

“The combination of precise stellar parameters, consistent multiband transit measurements, and the host star’s brightness makes TOI-4616 a particularly valuable system for future atmospheric and dynamical studies,” the authors write.