Astronomers using the James Webb Space Telescope have discovered that the ultra-short-period exoplanet TOI-561 b possesses a thick, highly reflective atmosphere capable of bouncing away roughly three-quarters of incoming starlight, challenging long-held theories that such heavily irradiated rocky worlds should be entirely bare rock.
Observations from the James Webb Space Telescope Reveal Unexpected Atmosphere
The rocky super-Earth TOI-561 b hugs its parent star so closely that a complete year takes just over 10 hours. Located approximately 280.5 light-years away in the constellation Sextans, the planet is part of one of the oldest and most metal-poor systems known in the Milky Way, with a host star roughly 10 billion years old. Because of its extreme proximity to its star, theorists expected the planet to be completely stripped of any gaseous envelope by intense stellar radiation. Instead, new data gathered by the NASA/ESA/CSA James Webb Space Telescope indicate it maintains a persistent, volatile-rich atmosphere.
Using the telescope’s NIRSpec instrument, researchers tracked the planet’s brightness across multiple eclipses and transits. The international team focused their work on measuring a phase curve, tracking how the system’s luminosity and heat evolved throughout the orbit. The resulting phase curve demonstrated that TOI-561 b reflects roughly 75% of the starlight hitting it, putting its reflectivity on par with Venus. Furthermore, heat distributes around the entire globe rather than concentrating solely on the permanent dayside.
We measured how the planet’s brightness and heat changed throughout its orbit. This technique, known as a phase curve, revealed that the planet reflects a significant amount of light from its star, and that heat is being redistributed around the planet instead of only on the sunlit side. Together, these point to the presence of an atmosphere.
Professor Lisa Dang, an astronomer at the University of Waterloo
Silicate Mineral Clouds Acting as a Planetary Sunscreen
To explain the unexpectedly cool dayside temperature and high albedo, astronomers compared their observational findings against computer climate simulations. While a bare, dark rock in that orbital slot should bake at roughly 3,200 K (about 4,900°F), JWST measured a brightness temperature closer to 2,050 K. The models suggest that the extreme heat vaporizes silicate minerals on the molten dayside, allowing them to rise and condense into bright clouds high above the surface.
These high-altitude clouds are rich in silicon dioxide and magnesium silicate, serving as a protective shield against the star’s blistering energy. The specific presence of quartz-like silicon dioxide is essential for achieving the high albedo needed by general circulation models to explain the observed dayside emission. Below this reflective ceiling, the planet’s surface is likely dominated by a global ocean of magma acting as a vast, planet-wide volcano.
This raises major questions such as whether the planet started with an unusually large supply of gases or if the ocean of molten rock covering its surface, acts as a planet-wide volcano that is constantly feeding its atmosphere.
Dr Anjali Piett, an astronomer at the University of Birmingham
Challenging Exoplanet Evolution Theories for Ultra-Short-Period Worlds
The findings published in The Astronomical Journal disrupt standard models of atmospheric escape for ultra-short-period rocky planets. Researchers point out that while the current exoplanet census often portrays similarly irradiated super-Earths as desiccated, bare rocks, TOI-561 b proves that some bodies retain substantial volatile envelopes.
Scientists are exploring several scenarios to explain how the world held onto its shroud for billions of years. The planet may have migrated inward from a safer, more distant orbit after the host star calmed down, or it might have begun life as a volatile-rich sub-Neptune before losing its outer layers. Another intriguing possibility suggests that atmospheric gases were initially sequestered deep inside the planetary interior during a magma ocean phase and later released through prolonged outgassing.
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- University of Waterloo researchers claim discovery of atmosphere on super-Earth exoplanet TOI-561 b (newsy-today.com)
- JWST Finds Reflective Atmosphere on Super-Earth TOI-561b (world-today-journal.com)
