# Spectroscopic time series performance of the Mid-Infrared Instrument on the JWST

**Authors:** Jeroen Bouwman, Sarah Kendrew, Thomas P. Greene, Taylor J. Bell, Pierre-Olivier Lagage, Juergen Schreiber, Daniel Dicken, G. C. Sloan, Nestor Espinoza, Silvia Scheithauer, Alain Coulais, Ori D. Fox, Rene Gastaud, Adrian M. Glauser, Olivia C. Jones, Alvaro Labiano, Fred Lahuis, Jane E. Morrison, Katherine Murray, Michael Mueller  
**arXiv:** [2211.16123](https://arxiv.org/abs/2211.16123)  
**Date:** 2022-11-29  
**Summary page:** https://www.summarizepaper.com/en/arxiv-id/2211.16123v2/

## Key points

- The Mid-Infrared Instrument (MIRI) on the James Webb Space Telescope enabled the first-ever mid-infrared spectroscopic time series observation of a transiting exoplanet, L 168-9 b.
- Two independent analyses of a single transit observation achieved a spectro-photometric precision of approximately 50 ppm in the 7-8 \micron range at R=50, consistent with systematic noise of approximately 25 ppm.
- The measured noise in L 168-9 b's transmission spectrum is approximately 15-20 \% higher than random noise simulations over wavelengths $6.8 \lesssim \lambda \lesssim 11$ $\mu$m.
- An excess noise up to a factor of two was observed at shorter wavelengths, and possible causes are discussed.
- This groundbreaking observation provides valuable insights into exoplanetary atmospheres and their composition.
- By studying exoplanets' atmospheres, scientists can gain a better understanding of how they form and evolve over time.
- This information can also help identify potentially habitable planets outside our solar system and pave the way for future missions to explore them further.
- Overall, this study highlights the importance and capabilities of advanced technology like MIRI in advancing our understanding of exoplanets and their environments.

## Summary

The Mid-Infrared Instrument (MIRI) on the James Webb Space Telescope has enabled the first-ever mid-infrared spectroscopic time series observation of a transiting exoplanet, L 168-9 b. 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. With limited in-flight calibration data, two independent analyses of a single transit observation achieved a spectro-photometric precision of approximately 50 ppm in the 7-8 \micron range at R=50, consistent with systematic noise of approximately 25 ppm. The derived band averaged transit depth is within 1 $\sigma$ of the known transit depth at 524 $\pm$ 15 ppm and 547 $\pm$ 13 ppm for the two applied analysis methods, respectively. The measured noise in L 168-9 b's transmission spectrum is approximately 15-20 \% higher than random noise simulations over wavelengths $6.8 \lesssim \lambda \lesssim 11$ $\mu$m. However, an excess noise up to a factor of two was observed at shorter wavelengths, and possible causes are discussed. These results demonstrate MIRI's future potential for characterizing exoplanet atmospheres. This groundbreaking observation provides valuable insights into exoplanetary atmospheres and their composition. By studying exoplanets' atmospheres, scientists can gain a better understanding of how they form and evolve over time. This information can also help identify potentially habitable planets outside our solar system and pave the way for future missions to explore them further. Overall, this study highlights the importance and capabilities of advanced technology like MIRI in advancing our understanding of exoplanets and their environments. It demonstrates that such technologies have great potential to revolutionize our knowledge about extraterrestrial worlds and open up new possibilities for space exploration in years to come.