Scientists Uncover Atmosphere on 1,800°C Exoplanet TOI-561 b

A team of UK scientists has made a groundbreaking discovery of an atmosphere surrounding the ultra-hot exoplanet known as TOI-561 b, located approximately 280 light years from Earth. Utilizing data from the James Webb Space Telescope, researchers have found the strongest evidence yet for gaseous layers enveloping this rocky planet, which experiences scorching daytime temperatures of around 1,800°C.

The findings challenge long-held assumptions about the capacity of smaller planets in close proximity to their stars to retain atmospheres. Lead author Johanna Teske, a staff scientist at the Carnegie Science Earth and Planets Laboratory, highlighted the significance of TOI-561 b’s surprisingly low density. “What really sets this planet apart is its anomalously low density,” she stated, noting that it is less dense than expected for a planet with an Earth-like composition.

A Unique Orbital Environment

TOI-561 b orbits a very old, iron-poor star that is twice as old as our Sun, situated in a region of the Milky Way known as the thick disk. This unique position suggests that the planet likely formed in a different chemical environment compared to those in our solar system. With a radius approximately 1.4 times that of Earth, TOI-561 b belongs to a rare group of celestial bodies called ultra-short period exoplanets.

Despite its proximity to its host star—less than one million miles, or one-fortieth the distance between Mercury and the Sun—scientists had previously assumed that the intense stellar radiation would strip away any atmosphere. However, the data gathered indicates otherwise.

Researchers utilized the telescope’s NIRSpec (Near-Infrared Spectrograph) to assess the planet’s dayside temperature by measuring its near-infrared brightness. This method involved observing the decrease in brightness of the star-planet system as TOI-561 b passed behind its star, similar to techniques used in studying atmospheres of other rocky worlds.

New Insights into Planetary Atmospheres

Expectations were that if TOI-561 b were a bare rock, its dayside temperature would approach 2,700°C (around 4,900°F). Instead, the observations revealed a temperature closer to 1,800°C (approximately 3,200°F), suggesting a significant atmospheric presence. The research team speculated that the magma ocean on the planet’s surface might help circulate heat, but without an atmosphere, the nightside would likely remain solid, limiting any heat distribution.

In an article published in The Astrophysical Journal Letters, the researchers argued that a robust, volatile-rich atmosphere is essential to account for the observations. Co-author Dr. Anjali Piette from the University of Birmingham noted, “We really need a thick volatile-rich atmosphere to explain all the observations.” She explained that strong winds in this atmosphere could redistribute heat, cooling the dayside.

Another potential explanation for the planet’s low density could be its composition, which may include a relatively small iron core and a mantle less dense than Earth’s. While the findings provide compelling evidence for an atmosphere, questions remain regarding how such a small planet, subjected to extreme radiation, could retain a substantial gaseous layer.

Co-author Tim Lichtenberg from the University of Groningen suggested a balance between the magma ocean and the atmosphere. He articulated, “While gases are coming out of the planet to feed the atmosphere, the magma ocean is sucking them back into the interior.” He emphasized that TOI-561 b must be significantly more volatile-rich than Earth to account for the data, likening it to a “wet lava ball.”

The James Webb Space Telescope continues to play a crucial role in advancing our understanding of distant worlds, probing the origins of the universe and solving mysteries within our own solar system. This latest discovery not only expands our knowledge of exoplanets but also raises important questions about the formation and evolution of planetary atmospheres.