2025-12-12 バーミンガム大学
Super-Earth Exoplanet TOI-561 b – image by NASA/STScI
＜関連情報＞
- https://www.birmingham.ac.uk/news/2025/scientists-detect-atmosphere-on-molten-rocky-exoplanet
- https://iopscience.iop.org/article/10.3847/2041-8213/ae0a4c
超高温超地球TOI-561 bの厚い揮発性大気 A Thick Volatile Atmosphere on the Ultrahot Super-Earth TOI-561 b
Johanna K. Teske, Nicole L. Wallack, Anjali A. A. Piette, Lisa Dang, Tim Lichtenberg, Mykhaylo Plotnykov, Raymond Pierrehumbert, Emma Postolec, Samuel Boucher, Alex McGinty,…
The Astrophysical Journal Letters Published: 2025 December 11
DOI:10.3847/2041-8213/ae0a4c
Abstract
Ultrashort-period (USP) exoplanets—with Rp ≤ 2R⊕ and periods ≤1 day—are expected to be stripped of volatile atmospheres by intense host star irradiation, which is corroborated by their nominal bulk densities and previous eclipse observations, consistent with bare-rock surfaces. However, a few USP planets appear anomalously underdense relative to an Earth-like composition, suggesting an exotic interior structure (e.g., coreless) or a volatile-rich secondary atmosphere increasing their apparent radius. Here, we present the first dayside emission spectrum of the low-density (4.3 ± 0.4 g cm−3) USP planet TOI-561 b, which orbits an iron-poor, alpha-rich, ∼10 Gyr old thick-disk star. Our 3–5 μm JWST/NIRSpec observations demonstrate the dayside of TOI-561 b is inconsistent with a bare-rock surface at high statistical significance, suggesting instead a thick volatile envelope that is cooling the dayside to well below the ∼3000 K expected in the bare-rock or thin-atmosphere case. These results reject the popular hypothesis of complete atmospheric desiccation for highly irradiated exoplanets and support predictions that planetary-scale magma oceans can retain substantial reservoirs of volatiles, opening up the geophysical study of ultrahot super-Earths through the lenses of their atmospheres.
