2025-09-10 ミシガン大学
The Earth-size exoplanet TRAPPIST-1 e, depicted at the lower right, is silhouetted as it passes in front of its flaring host star in this artist’s concept of the TRAPPIST-1 system. Scientists call this event a transit, when valuable data can be gathered as the exoplanet passes between the star and the telescope and starlight illuminates the atmosphere, if one is present. Image credit: NASA, ESA, CSA, STScI, Joseph Olmsted (STScI)
＜関連情報＞
- https://news.umich.edu/the-skys-a-limit-studying-the-atmosphere-of-a-potentially-habitable-planet-40-light-years-away/
- https://iopscience.iop.org/article/10.3847/2041-8213/adf42e
- https://iopscience.iop.org/article/10.3847/2041-8213/adf62e
JWST-TST DREAMS：居住可能領域惑星TRAPPIST-1 eのNIRSpec/PRISM透過分光観測 JWST-TST DREAMS: NIRSpec/PRISM Transmission Spectroscopy of the Habitable Zone Planet TRAPPIST-1 e
Néstor Espinoza, Natalie H. Allen, Ana Glidden, Nikole K. Lewis, Sara Seager, Caleb I. Cañas, David Grant, Amélie Gressier, Shelby Courreges, Kevin B. Stevenson,…
The Astrophysical Journal Letters Published: 2025 September 8
DOI:10.3847/2041-8213/adf42e
Abstract
TRAPPIST-1 e is one of the very few rocky exoplanets that is both amenable to atmospheric characterization and resides in the habitable zone of its star—located at a distance from its star such that it might, with the right atmosphere, sustain liquid water on its surface. Here, we present a set of four JWST/NIRSpec PRISM transmission spectra of TRAPPIST-1 e obtained in mid-to-late 2023. Our transmission spectra exhibit similar levels of stellar contamination as observed in prior works for other planets in the TRAPPIST-1 system but over a wider wavelength range, showcasing the challenge of characterizing the TRAPPIST-1 planets even at relatively long wavelengths (3–5 μm). While we show that current stellar modeling frameworks are unable to explain the stellar contamination features in our spectra, we demonstrate that we can marginalize over those features instead using Gaussian processes, which enables us to perform novel exoplanet atmospheric inferences with our transmission spectra. In particular, we are able to rule out cloudy, primary H2-dominated (≳80% by volume) atmospheres at better than a 3σ level. Constraints on possible secondary atmospheres on TRAPPIST-1 e are presented in a companion paper. Our work showcases how JWST is breaking ground in the precision needed to constrain the atmospheric composition of habitable-zone rocky exoplanets.
JWST-TST DREAMS：居住可能領域惑星TRAPPIST-1 eの二次大気制約 JWST-TST DREAMS: Secondary Atmosphere Constraints for the Habitable Zone Planet TRAPPIST-1 e
Ana Glidden, Sukrit Ranjan, Sara Seager, Néstor Espinoza, Ryan J. MacDonald, Natalie H. Allen, Caleb I. Cañas, David Grant, Amélie Gressier, Kevin B. Stevenson,…
The Astrophysical Journal Letters Published: 2025 September 8
DOI:10.3847/2041-8213/adf62e
Abstract
The TRAPPIST-1 system offers one of the best opportunities to characterize temperate terrestrial planets beyond our own solar system. Within the TRAPPIST-1 system, planet e stands out as highly likely to sustain surface liquid water if it possesses an atmosphere. Recently, we reported the first JWST/NIRSpec PRISM transmission spectra of TRAPPIST-1 e, revealing significant stellar contamination, which varied between the four visits. Here, we assess the range of planetary atmospheres consistent with our transmission spectrum. We explore a wide range of atmospheric scenarios via a hierarchy of forward modeling and retrievals. We do not obtain strong evidence for or against an atmosphere. Our results weakly disfavor CO2-rich atmospheres for pressures corresponding to the surface of Venus and Mars and the cloud tops of Venus at 2σ. We exclude H2-rich atmospheres containing CO2 and CH4 in agreement with past work but find that higher mean molecular weight, N2-rich atmospheres with trace CO2 and CH4 are permitted by the data. Both a bare rock and N2-rich atmospheric scenario provide adequate fits to the data but do not fully explain all features, which may be due to either uncorrected stellar contamination or atmospheric signals. Ongoing JWST observations of TRAPPIST-1 e, exploiting consecutive transits with TRAPPIST-1 b, will offer stronger constraints via a more effective stellar contamination correction. The present work is part of the JWST Telescope Scientist Team Guaranteed Time Observations, which is performing a Deep Reconnaissance of Exoplanet Atmospheres through Multi-instrument Spectroscopy (DREAMS).
