Researchers utilizing NASA’s James Webb Space Telescope have uncovered the strongest evidence yet of an atmosphere enveloping a rocky exoplanet, TOI-561 b. This ultra-hot super-Earth, located outside our solar system, is believed to be cloaked by a thick layer of gases above a global magma ocean. The findings, published today in The Astrophysical Journal Letters, offer fresh insights into the planet’s low density and challenge the prevailing belief that small planets in close proximity to their stars cannot sustain atmospheres.
TOI-561 b, with a radius 1.4 times that of Earth and an orbital period of less than 11 hours, belongs to a rare class of celestial bodies known as ultra-short period exoplanets. Despite its host star being slightly smaller and cooler than the Sun, TOI-561 b orbits at a perilously close distance—less than one million miles, or one-fortieth the distance between Mercury and the Sun—resulting in a tidally locked state with extremely high temperatures on its permanent dayside.
Challenging Prevailing Theories
The discovery that TOI-561 b may possess a thick atmosphere contradicts the long-held assumption that such small, close-orbiting planets are mere barren rocks. Dr. Anjali Piette from the University of Birmingham emphasized the necessity of a volatile-rich atmosphere to account for the observations. “Strong winds would cool the dayside by transporting heat over to the nightside,” she explained. “Gases like water vapor would absorb certain wavelengths of near-infrared light emitted by the surface before they ascend through the atmosphere.”
Lead author Johanna Teske, a staff scientist at Carnegie Science Earth and Planets Laboratory, highlighted the planet’s unique characteristics. “What really sets this planet apart is its anomalously low density,” she noted. “TOI-561 b is distinct among ultra-short period planets as it orbits a very old, iron-poor star—twice as old as our sun—within the Milky Way’s thick disk.”
Investigating the Atmosphere
The research team employed Webb’s NIRSpec (Near-Infrared Spectrograph) to measure the planet’s dayside temperature based on its near-infrared brightness. This technique, akin to those used in studies of the TRAPPIST-1 system, involves measuring the decrease in brightness of the star-planet system as the planet moves behind the star. If TOI-561 b were a bare rock without an atmosphere, its dayside temperature would be expected to approach 4,900 degrees Fahrenheit (2,700 degrees Celsius). However, observations indicate a cooler temperature of approximately 3,200 degrees Fahrenheit (1,800 degrees Celsius).
To explain these findings, the team considered several scenarios. While a magma ocean might circulate some heat, the absence of an atmosphere would result in a solid nightside, limiting heat distribution. A thin layer of rock vapor on the magma ocean’s surface could contribute to cooling, but not to the extent observed.
Implications for Planetary Science
The discovery raises intriguing questions about how a small planet like TOI-561 b can maintain such a substantial atmosphere despite intense stellar radiation. Co-author Tim Lichtenberg from the University of Groningen suggested an equilibrium between the magma ocean and the atmosphere. “While gases are emitted to feed the atmosphere, the magma ocean absorbs them back into the interior,” he explained. “This planet must be much more volatile-rich than Earth.”
These findings are the first from Webb’s General Observers Program 3860, which involved over 37 hours of continuous observation while TOI-561 b completed nearly four full orbits of its star. The research team is now analyzing the complete data set to map the planet’s temperature and further investigate the composition of its atmosphere.
Looking Forward
The James Webb Space Telescope, a collaborative effort between NASA, the European Space Agency, and the Canadian Space Agency, continues to unravel the mysteries of our universe. By exploring distant worlds and probing the origins of cosmic structures, Webb is enhancing our understanding of the cosmos and our place within it.
As researchers delve deeper into the data, the implications of this discovery could reshape our understanding of planetary formation and atmospheric retention, particularly for planets formed in environments vastly different from our own solar system.
