This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Among Kepler and TESS's many surprising exoplanet discoveries are the ultra-short-period (USP) planets. These planets move very quickly and complete an orbit in less than 24 hours.
Ancient astronomers thought that Mercury was so fast—it goes around the sun every 88 days—that they named it after the Roman god Mercury, who was the fast-traveling messenger of the gods. They couldn't have known how sluggish Mercury is compared to the USPs. Their speed is just one of their remarkable qualities.
Since they're so close to their stars, USPs are exposed to the full, blazing force of their stars' powerful radiation. This means these planets should have lost their atmospheres to space. But one USP named TOI-561 b seemed to be different.
Early observations detected hints of an atmosphere, and a 2025 paper based on limited JWST observations suggested it had an atmosphere made of volatiles like water and carbon dioxide. Now, some of the same researchers revisited the exoplanet. The new work used the JWST to examine the exoplanet's atmosphere in more detail.
The research is "A Highly Reflective Atmosphere on the Lava World TOI-561b Revealed by JWST/NIRSpec Phase Curves," and it's published in The Astronomical Journal. The first author is Samuel Boucher from the Department of Physics and Trottier Institute for Research on Exoplanets at the Université de Montréal, Canada. "One of the most pressing questions in exoplanet science today is whether small rocky exoplanets can host atmospheres," the authors write.
If they do, scientists expect these atmospheres to be secondary rather than primordial. Some portion of the atmosphere could come from off-gassing or other exchanges with the exoplanet's interior, and that is evidence of processes that are not visible in remote observations. That has implications for understanding how rocky planets evolve and how habitability may arise.
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