Exoplanet Atmosphere Report · JWST NIRSpec/PRISM

TRAPPIST-1 e

One of the most Earth-like planets known by size and insolation, orbiting an ultracool dwarf 12.4 parsecs away, and one of JWST's highest-priority habitable-zone targets. This page tests its own decontaminated NIRSpec/PRISM transmission spectrum for flatness and reports the result next to Espinoza et al. (2025)'s published atmosphere constraints.

Transit-discovered, 2017 NASA Exoplanet Archive parameters JWST NIRSpec/PRISM spectrum, 4 visits (Espinoza et al. 2025)
Artist's concept of the rocky habitable-zone exoplanet TRAPPIST-1 e

AI-generated artist's concept of TRAPPIST-1 e — not a real photograph. All data and figures in this report come from actual JWST NIRSpec/PRISM observations (see below).

The planet, in numbers

Queried live from the NASA Exoplanet Archive TAP service (pscomppars).

Radius0.92 Earth radii
Mass0.69 Earth masses
Orbital period6.10 days
Semi-major axis0.0293 AU
Equilibrium temperature249.7 K (within the conventional habitable zone for its ultracool host)
Host starTRAPPIST-1, ultracool M8V dwarf, Teff = 2566 K, 0.119 Rsun, 0.090 Msun
Distance12.4 parsecs (~40.5 light-years)
Discovery2017, transit photometry (TRAPPIST + Spitzer + K2)

A crowded, temperate system built for atmosphere-hunting

TRAPPIST-1 is a system of seven roughly Earth-sized rocky planets around an ultracool M dwarf, discovered by the TRAPPIST, Spitzer, and K2 surveys and refined through years of follow-up. Planet e sits in the conventional habitable zone, and its small, cool, nearby host star gives an unusually favorable transit depth for atmospheric spectroscopy on a rocky planet — one of the reasons it's a flagship JWST target despite its Earth-like size.

Espinoza et al. (2025), part of the JWST-TST DREAMS program, combined four NIRSpec/PRISM transits of TRAPPIST-1e and corrected the resulting spectrum for contamination from unocculted starspots and faculae on the host star — a real, significant systematic for any planet transiting an active M dwarf, since spots and faculae imprint their own wavelength-dependent signal on the transit depth independent of the planet's atmosphere.

Close-up 3D-rendered concept of TRAPPIST-1 e's rocky surface

AI-generated 3D-render-style concept — one of several atmosphere scenarios still statistically consistent with the flat spectrum below, not a confirmed depiction.

Final spectrum and reduction-sensitivity audit

The figure separates three questions: the diagonal constant fit to the final GP-decontaminated spectrum; the weighted mean transit depth from six reductions of each visit; and the residual structure left by a constant-depth model. The six reductions of a visit share the same observation and are not independent replicates.

Three-panel TRAPPIST-1e audit showing the final spectrum, depth by visit and pipeline, and constant-fit residual structure
Final 67-bin product plus 24 published pipeline/visit spectra. NIRSpec/PRISM's resolving power is wavelength-dependent, R~30-300; "R10000" in a source filename labels an internal resampling grid. Generated by scripts/analyze_spectrum.py.
Flat-line deviation-5.0 ppm
χ² / dof42.85 / 66
Reduced χ² (this page)0.65
p-value0.988
Standardized-residual RMS0.800
Visit 104 median offset−360.2 ppm
H2-rich atmosphere rejection (paper)>3σ

The final product does not reject a fitted constant under this diagonal-error likelihood. Its reduced χ² of 0.649 and standardized-residual RMS of 0.800 may reflect conservative marginal errors and/or covariance that this calculation omits; p = 0.988 is not proof that no atmosphere exists. Across all six reductions, visit 104 is lower than visits 001–003; its median weighted depth is 4715.2 ppm, 360.2 ppm below the median of the earlier visit medians, and its between-pipeline range reaches 160.0 ppm. This is a visit-level systematic-sensitivity diagnostic, not a planetary-atmosphere detection. Espinoza et al. (2025)'s full retrieval—not this audit—rules out cloudy primary atmospheres with at least 80% H2 by volume at better than 3σ.

Data and method notes

System parameters come from the NASA Exoplanet Archive TAP service. The final product and the 24 pipeline/visit tables come from the authors' Zenodo archive—see data/SOURCE.md and the pipeline-product provenance. The complete audit is in scripts/analyze_spectrum.py; machine-readable results are available as JSON and CSV. These descriptive diagonal-error fits neither reproduce the paper's covariance model nor perform atmospheric retrieval or model selection.

AI-generated illustration of the James Webb Space Telescope

AI-generated illustration of the James Webb Space Telescope, whose NIRSpec instrument took the real PRISM transit spectra used in this report. Not an official mission photograph — see NASA/JWST for real imagery.

References

  1. Gillon, M. et al., 2017. Seven temperate terrestrial planets around the nearby ultracool dwarf star TRAPPIST-1. Nature, 542, pp.456-460.
  2. Espinoza, N. et al., 2025. JWST-TST DREAMS: NIRSpec/PRISM Transmission Spectroscopy of the Habitable Zone Planet TRAPPIST-1 e. The Astrophysical Journal Letters, 990(2), L52 (arXiv:2509.05414).
  3. Glidden, A. et al., 2025. JWST-TST DREAMS: Secondary Atmosphere Constraints for the Habitable Zone Planet TRAPPIST-1 e. The Astrophysical Journal Letters, 990(2), L53.
  4. Agol, E. et al., 2021. Refining the Transit-timing and Photometric Analysis of TRAPPIST-1: Masses, Radii, Densities, Dynamics, and Ephemerides. The Planetary Science Journal, 2, 1.
  5. NASA Exoplanet Archive, exoplanetarchive.ipac.caltech.edu — system parameters, queried live via TAP.