ウェッブ宇宙望遠鏡、岩石質太陽系外惑星を取り巻く大気の可能性を示唆(NASA’s Webb Hints at Possible Atmosphere Surrounding Rocky Exoplanet)

2024-05-08 NASA

This artist’s concept shows what the exoplanet 55 Cancri e could look like based on observations from NASA’s James Webb Space Telescope and other observatories. Observations from Webb’s NIRCam and MIRI suggest that the planet may be surrounded by an atmosphere rich in carbon dioxide (CO2) or carbon monoxide (CO). Researchers think the gases that make up the atmosphere could have bubbled out of an ocean of magma that is thought to cover the planet’s surface.　NASA, ESA, CSA, Ralf Crawford (STScI)

＜関連情報＞

• https://science.nasa.gov/missions/webb/nasas-webb-hints-at-possible-atmosphere-surrounding-rocky-exoplanet/
• https://www.nature.com/articles/s41586-024-07432-x

岩石で覆われた太陽系外惑星55カンクリの二次大気 A secondary atmosphere on the rocky Exoplanet 55 Cancri e

Renyu Hu,Aaron Bello-Arufe,Michael Zhang,Kimberly Paragas,Mantas Zilinskas,Christiaan van Buchem,Michael Bess,Jayshil Patel,Yuichi Ito,Mario Damiano,Markus Scheucher,Apurva V. Oza,Heather A. Knutson,Yamila Miguel,Diana Dragomir,Alexis Brandeker & Brice-Olivier Demory
Nature  Published:08 May 2024
DOI:https://doi.org/10.1038/s41586-024-07432-x

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Abstract

Characterizing rocky exoplanets is a central endeavor of astronomy, and yet the search for atmospheres on rocky exoplanets has hitherto resulted in either tight upper limits on the atmospheric mass^1–3 or inconclusive results^4–6. The 1.95-R_Earth and 8.8-M_Earth planet 55 Cnc e, with a predominantly rocky composition and an equilibrium temperature of ~2000 K, may have a volatile envelope (containing molecules made from a combination of C, H, O, N, S, and P elements) that accounts for up to a few percent of its radius^7–13. The planet has been observed extensively with transmission spectroscopy^14–22, and its thermal emission has been measured in broad photometric bands^23–26. These observations disfavor a primordial H₂/He-dominated atmosphere but cannot conclusively determine whether the planet has a secondary atmosphere^27,28. Here we report a thermal emission spectrum of the planet obtained by JWST’s NIRCam and MIRI instruments from 4 to 12 μm. The measurements rule out the scenario where the planet is a lava world shrouded by a tenuous atmosphere made of vaporized rock^29–32, and indicate a bona fide volatile atmosphere likely rich in CO₂ or CO. This atmosphere can be outgassed from and sustained by a magma ocean.