Scientists Discover Atmosphere Surrounding Exotic Exoplanet TOI-561 b

Researchers have uncovered compelling evidence supporting the existence of an atmosphere on the rocky exoplanet TOI-561 b, challenging existing beliefs about small planets near their stars. Located approximately 280 light-years from Earth, TOI-561 b orbits a star that is around 10 billion years old and features a vast magma ocean, according to a study utilizing NASA’s Webb Space Telescope.

The study, published in The Astrophysical Journal Letters, marks a significant advancement in understanding the characteristics of rocky planets beyond our solar system. Previous theories suggested that planets in close proximity to their stars could not maintain a thick atmosphere due to extreme temperatures and stellar radiation. However, the findings related to TOI-561 b indicate otherwise.

Unusual Densities and Temperatures

Originally discovered in 2020, TOI-561 b is the innermost of at least three planets orbiting a G-type star that is slightly smaller and cooler than our Sun. Its close orbit—less than 1 million miles from its host star—suggests the planet is likely tidally locked, meaning one side perpetually faces the star while the other remains in darkness. This unique positioning leads to scorching surface temperatures, previously thought to be too high for an atmosphere to exist.

“We found that TOI-561 b has an anomalously low density,” stated Johanna Teske, staff scientist at the Carnegie Science Earth and Planets Laboratory and lead author of the study. “It’s not a super-puff, but it is less dense than you would expect if it had an Earth-like composition.”

Typically, the intense radiation from the host star would cause any atmospheric gases to escape into space. Nonetheless, TOI-561 b’s low density suggests it possesses more than just a rocky surface, prompting scientists to investigate the planet’s composition further.

The research team employed Webb’s Near-Infrared Spectrograph (NIRSpec) to assess the dayside temperature of TOI-561 b, which is the side facing its star. They expected temperatures nearing 4,900 degrees Fahrenheit (approximately 2,700 degrees Celsius) if the planet lacked an atmosphere. Surprisingly, measurements indicated a temperature of around 3,200 degrees Fahrenheit (around 1,800 degrees Celsius), suggesting that an atmosphere could be present.

A Complex Relationship Between Magma and Atmosphere

The researchers considered alternative explanations for the temperature discrepancies, but none provided a satisfactory account. If TOI-561 b had no atmosphere, the nightside would likely be solid, preventing heat transfer from the hot dayside. The planet’s magma ocean could potentially contribute to this dynamic through a thin layer of rock vapor, but its cooling effect would be minimal.

“We really need a thick volatile-rich atmosphere to explain all the observations,” said Anjali Piette, a researcher at the University of Birmingham and co-author of the study.

The presence of an atmosphere raises further questions about how such a small planet, exposed to substantial radiation, can retain a thick veil of gases. The research team hypothesizes that the planet’s magma ocean plays a crucial role in this process.

“We think there is an equilibrium between the magma ocean and the atmosphere,” explained Tim Lichtenberg, a researcher at the University of Groningen and co-author of the study. “At the same time that gases are coming out of the planet to feed the atmosphere, the magma ocean is sucking them back into the interior.”

To account for the observations, Lichtenberg noted that TOI-561 b must be significantly more volatile-rich than Earth, leading to the description of the planet as “a wet lava ball.”

The findings regarding TOI-561 b not only deepen our understanding of exoplanets but also challenge existing paradigms regarding the conditions required for atmospheres to exist around rocky worlds.