Spectroscopic Time Series Performance of the Mid-infrared Instrument on the JWST

Jeroen Bouwman, Sarah Kendrew, Thomas P. Greene, Taylor J. Bell, Pierre Olivier Lagage, Jürgen Schreiber, Daniel Dicken, G. C. Sloan, Néstor Espinoza, Silvia Scheithauer, Alain Coulais, Ori D. Fox, René Gastaud, Adrian M. Glauser, Olivia C. Jones, Alvaro Labiano, Fred Lahuis, Jane E. Morrison, Katherine Murray, Michael MuellerOmnarayani Nayak, Gillian S. Wright, Alistair Glasse, George Rieke

Research output: Contribution to journalArticlepeer-review

15 Scopus citations


We present here the first ever mid-infrared spectroscopic time series observation of the transiting exoplanet L 168-9 b with the Mid-Infrared Instrument (MIRI) on the James Webb Space Telescope. The data were obtained as part of the MIRI commissioning activities, to characterize the performance of the Low Resolution Spectroscopy (LRS) mode for these challenging observations. To assess the MIRI LRS performance, we performed two independent analyses of the data. We find that with a single transit observation we reached a spectro-photometric precision of ∼50 ppm in the 7-8 μm range at R = 50, consistent with ∼25 ppm systematic noise. The derived band averaged transit depth is 524 ± 15 ppm and 547 ± 13 ppm for the two applied analysis methods, respectively, recovering the known transit depth to within 1σ. The measured noise in the planet’s transmission spectrum is approximately 15%-20% higher than random noise simulations over wavelengths 6.8 ≲ λ ≲ 11 μm. We observed an larger excess noise at the shortest wavelengths of up to a factor of two, for which possible causes are discussed. This performance was achieved with limited in-flight calibration data, demonstrating the future potential of MIRI for the characterization of exoplanet atmospheres.

Original languageEnglish (US)
Article number038002
JournalPublications of the Astronomical Society of the Pacific
Issue number1045
StatePublished - Mar 1 2023

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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